It's been a while since I last posted about my time in Bishop, California, back in September, when I attended a GSA field forum on the structural and neotectonic evolution of the volcanic tableland.

For reference, here's a list of the previous posts about that trip:
...Faults of the volcanic tableland
...The Bishop Tuff
...The flipping fault

So, picking up where I left off, I thought it would be worth a post to mention the gorgeous drainage channels one sees etched into the top "Ig2" welded layer of the Bishop Tuff. These channels are interpreted as being Pleistocene in age, when the area was wetter than it is now.

Here is a photograph of the most spectacular of these channels, as viewed from the rim:

We visited this vantage on our second day in the field. A hiking path at the bottom of the dry channel imparts a sense of scale.

Here's a Google Map of the area from the perspective of a hawk:

Where the road comes most closely tangential to the canyon is the point where we stopped to take a look at it, and where the above photograph was captured.

Further upstream along the channel, we find it broken by normal faulting. Check out the view across this graben (a graben is a normal-fault-bounded valley, downdropped relative to the highlands next to it). There, you see the distinctive crescent-shaped profile of the drainage channel, but offset along several fault scarps:

There are three scarps on the far side of the graben, and an additional one that Peter is standing on, on this side of the graben. Just behind Peter, you can see a broken relay ramp, too. View is to the northwest; those are the Sierras in the distance.

Here is a Google Map of the area, showing the drainage channel crossing the graben. This conclusively shows that the channel must be older than the faulting which produced the graben.

This Google Map shares its southeastern corner with the northwestern corner of the first one I showed. You can see this for yourself by dragging either one in the appropriate direction. They both share the white-knuckled place where the road goes straight down the fault scarp, rather than sensibly down a relay ramp. That wasn't my favorite thing to drive.

Here's another drainage channel, similarly bone dry, that we visited in our fourth day in the field. Perspective is to the east: those are the White Mountains in the distance:


The Google Map shows a more interesting relationship this time. Instead of the faulting cross-cutting the channel's orientation, this channel approaches the graben to the southeast, curves around (deflecting from its original downhill course) and drops down the relay ramp to the northeast, into the graben (breaking up into multiple channels en route). There, it resumes its original downhill trajectory to the southeast:

This suggests that at least some of these faults were rupturing the "Ig2" layer at the same time that water was flowing over the surface (i.e. before the Owens Valley's climate dried out, post-Pleistocene). The stream's course and the faulting were coeval.

So what was the source of these streams? Did they originate on the volcanic tableland, or were they derived from the Sierra Nevada, prior to incision by the Owens River (which makes a deep canyon a mile or two west of here)? Fred Phillips, of New Mexico Tech, holds up a piece of evidence:

That is not a rounded cobble of the Bishop Tuff. That's a rounded cobble of granite. While the majority of cobbles in these channels are locally-derived chunks of the Bishop Tuff, there are also clasts which originated elsewhere, beyond the volcanic tableland itself. This suggests a source area with a granitic outcrop. One candidate location is Casa Diablo Mountain, north of the (south-sloping) volcanic tableland. Another possibility is the Sierras, to the west.

Another possibility entirely is that the source of the cobbles could be anywhere, and they were brought to the volcanic tableland not by streams but by paleoindians, who used them as grain-grinding stones in their metates.

Labels: california, conferences, faults, granite, pleistocene, rivers, travel, volcano, weathering

Here's the group photo from the field trip to the Boring Volcanic Field (before GSA in Portland, Oregon, this year). Credits: Diane Johnson-Cornelius (photographer) and Bill Leeman (camera).

Labels: meetings, oregon, volcano

On the day before the GSA meeting began, I participated in a field trip to the Boring Volcanic Field, a zone of anomalously-located volcanic vents around Portland, Oregon. The field is named for the Boring Hills, adjacent to the town of Boring, Oregon, which is named for a dude named "Boring." Kim Kastens noted this funny name on the Earth and Mind blog recently. The USGS maintains an information page on the field here.

Today, some photos...

Atop Rocky Butte, field trip leaders Rick Conrey (WSU) and Russ Evarts (USGS Menlo Park) orient the group with a map highlighting the various units comprising the Boring Volcanic Field:


Mount Hood hides its peak in the clouds:


At our first outcrop stop, the field trip participants get out and look at the Boring rocks:


Here, a Boring lava flow overlies Troutdale Formation fluvial gravels:


Annotated version for the untrained eye:


In places, a "baked" zone of contact metamorphism can be seen in the Troutdale as it got scorched by the lava that flowed on top of it (bright red), but the characteristic red color was missing underneath one spot, the central overhang in this photo:

Weird, huh? Maybe the metamorphosed sediments need a certain amount of rain-mediated chemical weathering before they "blush"?

Well-rounded clast from the Troutdale: vesicular basalt from the Columbia River Plateau:


Another nice Columbia River flood basalt boulder, this one with phenocrysts of plagioclase, and a concentric zonation of texture (massive in the center, vesicular towards the edges):


Plus, you can find cobbles derived from further afield: gneiss (from Idaho?), quartzite (Belt rock?), etc:


Between cobbles of the Troutdale, you can see hyaloclastic sand (immature sand with lots of hydrated basaltic glass fragments, apparently produced by interactions of magma and water in the source area, upstream):


More hyaloclastic sand:


Oooh! A "crack panel" on the side of some cooling columns at another stop! These horizontal slats are produced in individual fracture-propagation events, and each one concludes with a little ridge called an arrest line.


Mafic pyroclastics that underlie the lava flows at this second stop:


More mafic pyroclastics, on a cinder cone in Mount Tabor Park.


This is a pretty neat outcrop: you can see normal faults cutting these angle-of-repose inclined volcanic strata, presumably forming in slumping events.


Annotated version of this same photo, highlighting a marker layer and its offset along the fault:


The weather was pretty grim for this trip, so that was a bummer. But it's Portland, right? What did we really expect? Anyhow, I enjoyed being introduced to this suite of rocks -- boring out of context, but interesting given their location well west of the main axis of Cascade volcanism. Unfortunately, the field trip didn't really address why the Boring rocks are there. I was expecting some sort of detailed discussion of the possibilities: an evaluation of different models for their generation and passage to the surface... but that really didn't happen in any substantive way. So it wasn't the most amazing field trip I've ever gone on, but it was a nice day of checking out a cool suite of rocks.

Labels: meetings, oregon, pleistocene, pliocene, sediment, volcano

Here's a sample I collected along the road in the Sierra foothills when I was in California the weekend before last. It's a nice little hand sample of amygdules: vesicles (lava degassing bubbles) that have gotten infilled with mineral deposits. I just slapped it on the scanner along with a penny. Enjoy!

Labels: igneous, primary structures, volcano

A Swim Through the Ocean's Future.

Hat tip to the Volcanism Blog for alerting me to this.

Labels: ocean acidfication, volcano

There's been a lot of hubbub in the geoblogosphere over the past couple of days about caldera-forming eruptions. The trigger for all the discussion was a report about a really old (Permian) caldera-forming eruption in Italy. This invokes discussion of our modern worry-inducing "supervolcanos," like Yellowstone. There's also a lesser-known place in California, where the USGS maintains a volcano observatory there just like they do with Yellowstone: Long Valley Caldera. This caldera formed ~760,000 years ago, and deposited a lot of ash, collectively called the Bishop Tuff. The Long Valley Caldera's true area is about 300 km², although central sagging has generated ring faults that give it a topographic area of ~350 km². The Bishop Tuff is thickest right around the caldera, but ash from this eruption can be found as far away as Nebraska.

I got to see the Bishop Tuff firsthand the week before last when I spent a week in the Owens Valley as part of a Geological Society of America Field Forum. I was lucky to be introduced to the tuff by Wes Hildreth, a volcanologist at the USGS's Menlo Park office. Wes "wrote the book" on the Bishop Tuff, and shared an immense amount of information and perspective with the Field Forum participants. I am indebted to him for all the information I'm sharing here. Maggie Mangan just took over the reins of the Long Valley Observatory, and she also participated in the Field Forum. I also really benefitted from talking to her about the eruption. (Any errors that you may find here, of course, are my own.)

The Bishop Tuff is the most striking of many volcanic eruptions along this same system. It's the only one that has produced a caldera. It was preceded by dacite and basalt eruptions at 3.5 to 2.5 Ma, and then by rhyolite and obsidian during the appropriately-named Glass Mountain Interval, from 2.1 to 0.8 Ma. (The Glass Mountain Interval is pretty cool in its own right: at least 60 eruptive units, each high-silica rhyolite!) The focus of both of these was further to the northeast. That area is also home to some post-Bishop eruptions, the youngest of which is at Mono Lake (only 250 years ago). In 1989, a dike came within a few km of the surface, and degassed a CO₂ "burp" which killed trees near Mammoth Mountain, which lies on the caldera boundary.

The Bishop Tuff is compositionally similar from bottom to top: it's all rhyolitic pyroclastics, whether it's welded (fused together) or not. Some went north from Long Valley Caldera under the Mono Lake area, while the bulk of it went south towards Bishop, forming the Volcanic Tableland. it has a density of about 1.5 g/cm³.

In this photo, Kim Bishop (yes, that's really his last name) and Peter Lovely (yes, that's really his last name) check out the first of the ashfall deposits, dumped atop lake sediments in a cool outcrop on the southern margin of the Volcanic Tableland, north of Bishop and the Owens River:


A close-up of this contact:

The ashfall portion of the Bishop Tuff has 9 subunits, and you can see the first (F1) and the base of the second (F2) here, overlying the silty lake sediments.

Here's another outcrop, in the Owens River Gorge, where you can see the welded ashflow "caprock" up top, and down below, and outcrop that showcases nonwelded ashfall and ashflow deposits. I've put a box around the area that I'll zoom into in the next photo:


The ashfall deposits are finely stratified and well-sorted, with no reworking. Overlying them, the first of the ashflow (ignimbrite) units shows characteristic poor sorting: big blobs of pumice mixed in with the finer pyroclastics. Most of the ashflow is pinkish in color, but you can see here that the first of it is white, same as the ashfall:

Why pink in the ashflow portion? It's hot when it gets deposited, and heat retention promotes oxidation. The earliest ashflows were dumped atop ashfall (which gets deposited cold), and so likely lost much of its heat downward; hence less oxidation. The entire eruptive seqence is preserved in the Volcanic Tableland north of Bishop. Here, at the southern rim of the Tableland, we're getting the latest flows. The earlier flows didn't make it this far south.

Here's a close-up of that basal ashflow, from the first outcrop. My field notebook is 18 cm "tall," for scale. Note the white color and all the large pumice clasts:

The iron to titanium ratio in these clasts suggests that they erupted at 770 to 800 degrees C. The temperature of the eruption increased as it progressed. This corresponds with an increase in the mafic content of the tephra over the course of the eruption. In the early layers, there's about 77.7% silica, but when you get towards the end of the eruption, you see that number drop to 74%, as well as a doubling of iron content, a quadrupling of the Ca content, and ten times as much magnesium as in the earliest strata.

Here's a close-up of some semi-welded material. This is float, so I don't know precisely where in the sequence it fits, but I would guess the "Ig1" layer, the lower of the two welded ashflows.


And another. One thing I noticed about a lot of the included pumice blobs is that their vesicles were all stretched out into cigar-shaped tubes (prolate), like an L-tectonite. Anyone have any idea what's up with that? I would expect oblate strain ellipsoids (pancake-shapes) here due to post-depositional compaction, but that's not what I noticed...


We made a trip to the lip of the Owens Gorge to look down on the upper ignimbrite (ashflow tuff) layers of the Bishop Tuff:


The first half of the eruptive sequence, dubbed "Ig1" (for "ignimbrite 1") is below the sharp line. In the upper half of the sequence, Ig2, you'll find rhyolite lithics that can be sourced to the earlier Glass Mountain Interval, as well as pyroxene-bearing pumice. You can see here some abortive cooling columns in Ig1:

Likely these don't extend very far down because as soon as they started forming, Ig1 was buried underneath piping hot Ig2 ashflow. This addition of heat disrupted the cooling front and truncated the fracturing process. Sorry I don't have a sense of scale in this photo: it's hard to do when you're photographing the opposite side of a deep gorge. I'd guess these columns are a meter or so across. In one spot, a little downstream (southeast) of here, you can actually see a little ashfall intercalated with these ashflows (it's the F9 ashfall subunit). This, Wes Hildreth told us, is most unusual and quite handy for interpreting the stratigraphy of the Bishop Tuff. The only other place he's seen such a thing is in the Valley of 10,000 Smokes in Katmai, Alaska.

Some close-ups of the Ig2 unit, which is classic "welded" tuff with nice pumice blobs and rhyolite lithics, as well as pyroxene-bearing pumice:


Rhyolite lithic clast in "Ig2" welded Bishop Tuff ashflow deposit:

That's likely from the earlier Glass Mountain Interval, through which the Bishop Tuff erupted.

The "Ig2" layer wasn't the last part of the Bishop Tuff eruptive sequence, but the stuff deposited on top of it was unwelded, and has since been eroded away. In order for a tuff to weld, it needs to be close to 600 degrees C when it stops (this temperature is for rhyolite: it's actually composition and H₂O dependent). But the welding process (essentially superhot glass fragments warp around one another and lock into place) has made for a resistant layer atop the modern Volcanic Tableland, and this layer preserves the weaker layers beneath, preventing them from being eroded (except, say, where a river incises downward through the caprock). It's a nice example of differential weathering. Cosmogenic ¹⁰Be measurements on the upper welded tuff suggest a modern weathering rate of 2 mm/1000 years.


Now here's the thing that I thought was most interesting about the Bishop Tuff: it's big, and it erupted quickly. There are about 200 km³ of ignimbrite (ashflow tuff), another 100 km³ of fallout (ashfall tuff) out to Utah and Nebraska, as well as 300 to 350 km³ of welded tuff that filled the downdropping caldera (2.5 km of subsidence). That's a lot of magma fluffed out and ejected onto the surface! But Wes calculated that this whole sequence, from the first puff of ash descending from above to the last of the sizzling nuee ardentes, lasted a mere 6 days: a single huge eruption! And, Wes added, "on the seventh day, it rested."

Further reading (I particularly recommend taking a look at Figure 5d!):
Hildreth, Wes, and Wilson, Colin, 2007. Compositional Zoning of the Bishop Tuff. Journal of Petrology 48 (5):951-999.

Labels: california, permian, pleistocene, volcano

I spent last week in the Owens Valley of California, attending a GSA field forum on the structure and neotectonics of the Owens Valley and the Volcanic Tableland north of Bishop. It was really cool, and I learned a lot. I'll be sharing images and ideas on the blog in days and weeks to come.

Twenty-four people attended, plus the three conveners: David Ferrill, Alan Morris, and Nancye Dawers. Here's the team getting an orientation on Monday morning, looking west towards the Sierra Nevada. Note the time-honored geology field tradition of using magnets to hold posters and maps to the side of the van:


David discusses the tectonics and geomorphology of the "Eastern California Shear Zone," a transtensional zone between the Sierra Nevada and the typical Basin & Range. This area ranges tremendously in elevation: from Mount Whitney in the Sierras (14,494' elevation) to Badwater in Death Valley (-282'). The lurid colors on this elevation map show that:


A Landsat photo comes out at the next stop, looking northeast towards the Volcanic Tableland:


And yet another image, this one a beautiful side-scanning radar image of the Volcanic Tableland, which David and Alan (here assisted by Wes Hildreth) pulled out at a stop overlooking the Owens River Gorge (a canyon which dissects the Volcanic Tableland):


This image shows east-dipping normal faults as white stripes, and west-dipping normal faults as dark stripes:


This is the main reason we're all here: the young welded ashflow deposits of the Bishop Tuff (760 ka) record brittle strain as a result of the past 760,000 years of extensional and strike-slip tectonics. Due to the low rainfall and this excellent marker unit, you can really get a sense of how such systems operate. The faults are expressed topographically: a lovely marriage of structure and geomorphology.

Our first overview of the Volcanic Tableland, looking northeast from the Sierra Nevada over the fractured Bishop Tuff, towards the White Mountains in the distance:


Here's a Google Map of the Volcanic Tableland, showing the orange upper ignimbrite layer of the Bishop Tuff, and the north-south trending faults which rupture it. Green stripes are the Round Valley (southwest), Owens River (southern border, trending east-west), and Fish Slough (far east, trending north-south):


Here's another Google Marp, zooming in on some of the faults. Conveniently, Google opted for morning sunlight in this image, so it's "color-coded" the same way as the side-scanning radar image I showed you earlier: east-dipping fault scarps are light-colored, while west-dipping fault scarps are in shadow:

(Another very cool thing about this image is the northwest-southeast trending Pleistocene drainage channel -- more on that later!)

Many of the faults in the Volcanic Tableland are arranged in en echelon arrays, reflecting a broader zone of deformation:


In en echelon arrays of these normal faults, we find the individual fault segments are linked up with intermediary flexures of the the ignimbrite layer, called "relay ramps." This was a new term to me, but once I learned it, I saw them everywhere. Here's one atop the Volcanic Tableland:

(It's the shallowly-sloped bit in the middle, dipping towards us, bounded by two west-dipping fault scarps: the intensely-shadowed areas.)

Here, in Fish Slough, we see a couple of 'relict' relay ramps that have gotten cut off as the small fault segments linked up into a larger through-going fault. Pretty cool!


The group descends a relay ramp on their way back from a field excursion to the vehicles:


Annotated version of the photo above:


Relay ramps occur on many scales. This 'scaling' of fault systems (and deformation in general) was a theme at the field forum. Here's a Google Terrain Map of the Owens Valley area. Notice how, just west of Bishop, the Sierra Nevada front jumps to the west? That's a much larger relay ramp, the Coyote Warp Relay Ramp:


Looking west from the first stop at the Sierras, with the Coyote Warp Relay Ramp descending from upper left towards lower right:


Annotated version of the photo above:

That's a little taste to get you started. More geology from the Owens Valley in future posts...

Labels: california, faults, structure, volcano

(Parts 1, 2, 3, 4, 5, & 6 of this series...)

Today's episode: The route down the mountain, and the long way back to camp.

After our "summit" of the arete between Hanging Canyon and Cascade Canyon, we begin carefully picking our way back downhill, switching between talus piles and snowfields, and back again:




We popped over the threshold, and started dropping down towards Jackson Hole. As the sun was dropping lower and lower in the sky to the west, we were pretty much in shadow from here on down... but the light still lingered on the highest peaks, like Teewinot Mountain, Mount Owen, and the Grand Teton itself:


By the time we got all the way back down to Jenny Lake, the sun was pretty much gone. However, it was illuminating a tall cloud north of us, sitting atop the Yellowstone area. We joked that this was the big one: Yellowstone had finally blown up and the orange color we were seeing wasn't "alpenglow" but incandescence from the long-awaited eruption of the Yellowstone volcanic center...


It wasn't, though. Just a little jest to take our minds off the fact that we had missed the last ferry across Jenny Lake, and so that meant adding an additional "2" (it sure felt more like 3) miles to our hike. As darkness closed in, we hoofed it along (only Pete had been prepared enough to bring a headlamp). For me, a highlight of this long slog came when Joel and I spotted an animal I'd heard of but never actually seen before: a pika! They are very, very cute animals that live in talus piles and make little squeaky noises. But they're quite elusive, at least in my experience. I've seen plenty of marmots and other alpine rodents, but this was my first Ewok pika.

We eventually got back to the vehicle and rolled back to camp, getting there about 10pm. We wolfed down some dinner, quenched our thirst, and sacked out. What a great day! In spite of being dog tired, I felt mentally rejuvenated and ready to take on the second half of the Rockies trip.

This post concludes the Hanging Canyon series. Thanks for coming along!

Labels: mammals, nova, travel, volcano, wyoming, yellowstone

The Crazy Mountains are a range of mountains in south-central Montana, north of Livingston:

In this Google Map, you can orient yourself from recent posts by finding Bozeman, the Gallatin Valley, and the Bridger Range down in the southwest corner.

The Crazys are an Eocene intrusion, (Ar/Ar dates of ~50 Ma), and they are beautifully expressed on a geologic map as a radiating series of dikes around two central blobs of intrusive rocks (quartz diorites, etc.: dark pink on the map):

These igneous intrusions penetrated the Livingston Group, a series of volcaniclastic sedimentary rocks of late Cretaceous to early Paleogene age (hot pink on the map).

The day before my students arrived in Montana this summer, Lily and I took a hike in the Crazys, entering in the northern part of the range. We saw some cool dikes exposed along the road on the way in. Here's me pointing out the contact between a subvertical dike of porphyritic andesite cutting across subhorizontal layers of the Livingston Group:


Annotated version of the same photograph:


And here's a close-up of the rock making up the dike; mostly fine-grained and gray, but with some lovely big euhedral plagioclase feldspars as well:


That's about it for the geology I saw in the Crazys. Our hike kept us mostly in the forest, so clearly I'm going to have to go back some other time and spend more time there!

Labels: igneous, montana, mountains, sediment, travel, volcano

by Anastashia Cuddihy*

Eleven miles south of Mammoth Hot Springs, and at the northern end of Beaver Lake in Yellowstone National Park, lies a geological wonder¹: Obsidian Cliff. Although it is only half a mile long, it has been a source of confusion and contentious debate for years.

Map of the Obsidian Cliff area (Google Maps):


Obsidian Cliff was formed when a rhyolitic lava flow traveled down the plateau and formed the 200 foot cliff. What is so unusual about the cliff is that obsidian is characterized by being a quickly cooled glass; the quick cooling prevents any crystals from forming, leading to a glassy rock. However, the bulk of the obsidian found at Obsidian Cliff is just that - a tall cliff made of obsidian - and it is far too massive to have cooled quickly enough to form obsidian in the 'traditional' way. Since there is no possibility that this amount of obsidian was cooled quickly, geologists theorize that the rhyolitic magma that formed the cliff had an extremely low water content, which would have hindered the formation of crystals. A feature found at the cliff that is associated with relatively slow cooling is columnar jointing. Columnar jointing occurs when lava shrinks during the cooling process, forming cracks, and it contracts to form 6-sided columns¹. Without the formation of crystals, the magma would have cooled to become the obsidian found in the cliff.

Columnar jointing at Obsidian Cliff:⁴


Another solution offered is that the lava could have come in contact with a large body of ice, such as a glacier¹. Upon contact with the glacier, the lava would have been able to cool rapidly and form the obsidian, although probably only at the contact margin. However the low-water-content explanation is the more widely accepted. Underlying the obsidian is a purplish-gray rhyolite, which is visible along the cliff face². Upon close examination of the obsidian, one can see the swirls left in it by the lava before it cooled¹.

Flow-banding in Obsidian Cliff obsidian:⁴

(also note the spherulites)

While Obsidian Cliff is not the only place in the park to find obsidian, it is most abundant at that site. Obsidian can also be found at locations called Tanker Curve and Cougar Creek.²

Obsidian Cliff is known for more than just being an anomaly in the formation of obsidian. Obsidian was prized by Native Americans for making tools, and there was no place better to find obsidian for these tools than Obsidian Cliff. Since obsidian fractures conchoidally and has sharp edges when fractured, it was best used in arrowheads and spears and blades for hunting¹. Scientists can use the chemical composition of obsidian (such as the concentrations of trace elements like rubidium and zirconium; See figure) to trace it to its source.

Scatterplot of zirconium (Zr) plotted versus rubidium (Rb) for 143 samples of artifact-quality obsidian collected in Yellowstone National Park.²


Archaeologists have concluded that obsidian from the cliff was being used as far back as 10,000 years ago, up until the arrival of Europeans in the area in the 1800's, when explorers found the Shoshone tribe using obsidian-tipped arrows³. Obsidan from the cliff has been found as far away as the midwestern United States, and it is inferred to have arrived there through the extensive Native American trade routes, where the high-quality obsidian would have been highly valued.

Obsidian Cliff is obviously an important site, both for American heritage and science. It gives us a wonderful idea of how the volcanic structures of the park work and how varied volcanic effects across the park can be. It is not suprising that a park with such a varied and explosive geological history would be home to such an intriguing structure.

__________________________________________________
* Rockies course 2009 student

1. http://www.nps.gov/yell/planyourvisit/upload/Yell250.pdf
2. http://www.obsidianlab.com/research/research_yellowstone.html
3. http://wyoshpo.state.wy.us/aamonth/2000.asp
4. Photo by Charlie Corrick.

Labels: volcano, wyoming, yellowstone

The Smithsonian's National Museum of Natural History, Department of Mineral Sciences invites the museum community to a memorial service commemorating the life contributions of Tom Simkin, the founding director of the Smithsonian's Global Volcanism Program. Simkin also served as president of the Geological Society of Washington. A memorial program will be held at Baird Auditorium on Tuesday, September 8 at 10:30 AM, followed by a reception in the Executive Conference Room. We welcome your attendance. Please send your RSVP (yes only) to Sally Kuhn Sennert (KUHNS@si.edu) by 1 September to help us make catering estimates for the reception.

Labels: gsw, museums, smithsonian, volcano

Working through my backlog of e-mails, I find that I have a few more Rockies course final projects to share with the world:

Laurie's website on Yellowstone geothermal features.

Jared explores Ringing Rocks.

Kevin suggests "more study is needed."

Ken discusses Grinnell Glacier:

Amanda reviews the Tetons:

Labels: glacial landforms, glaciation, montana, mountains, stromatolites, volcano, water resources, wyoming

On my first day in Montana this summer, I borrowed Lily's Jeep and set off to look for petrified wood in the Tom Miner Basin, an offshoot of the Paradise Valley (which connects Livingston to Gardiner). Along the way, though, I stopped at Point of Rocks CKCK, and found some nice exposures of the lahar deposits of the Absaroka/Gallatin Volcanic Field. These Eocene-aged extrusions basically consist of a series of lava flows and volcaniclastics interlayered to a substantial thickness.

Here's a map of Point of Rocks:


Here's the view north from Point of Rocks:


Here's some images of the rocks exposed there: poorly-sorted, matrix-supported grey conglomerates that I interpret on the basis of the previous year's field notes to be lahar deposits:




I've got a big fat chunk of this stuff in the NOVA geology lab now -- thanks to Lily for giving that forty pounds of lahar a lift cross-country!

Eventually I made it into the Tom Miner Basin, an area of Forest Service land where there is some petrified wood exposed. There is an interpretive trail where people are specifically asked NOT to collect but of course people collect anyhow, so it's kind of lame, but there are some nice examples of petrified branches and what not, and some nice examples of reverse-graded-bedding in the lahar deposits.

Map of the area where the road ends (at a campsite) and the trail begins:


Reverse graded bedding:


You can climb up above the trail to some exposures of the volcanics which are harder to get to and therefore not picked-over, and with a permit you can collect a fist-sized chunk per person per year.

Here's a couple examples of petrified wood that I saw:




More volcaniclastics, this time showing normal graded bedding (coarse at the bottom, fine at the top):


And on the way out, I saw a nice example of a couple of rugose corals cross-sectioned in a boulder of presumably-Mississippian-aged Madison Group limestone:



It was a nice first day in Montana! More photos to come...

Labels: fossils, igneous, montana, plants, volcano

On Saturday's Bedrock Geology of Washington, DC class, my students and I had the good fortune to stumble upon two geologists out doing field work: Tony Fleming, lead author of the geologic map of the Washington West quadrangle, and Steve Self, senior volcanologist with the Nuclear Regulatory Commission. They were out looking at the Sykesville Formation at Chain Bridge Flats, assessing a potential reinterpretation of the unit.

Fortunately, they were willing to take a little time and discuss their findings with the students. Here's a couple shots of Steve talking to the group:




I joined Steve and Tony in the field yesterday (Monday) too, looking at some outcrops on the other side of the river, and trying to make sense of them. Fun stuff! More on that at a later date...

Labels: dc, field trips, geologists, geology, igneous, metamorphism, nova, piedmont, sediment, volcano

Former student Stef sent me links to these videos over the weekend. It's a three-part series of Jake Lowenstern, the scientist-in-charge at Yellowstone Volcano Observatory, talking about Yellowstone and the work his team does there.

Part I:


Part II:


Part III:


Thanks Stef!

Labels: volcano, websites, yellowstone

Geological Society of Washington: Meeting 1432
Wednesday March 25, 2009

• Andrew Todd, US Geological Survey, Denver, Colorado - Abandoned Mines and Trout: The Interaction of Geochemistry, Metal Bioavailability, and Stream Ecology.
  
• Ian G. Macintyre, Smithsonian Institution, Washington, DC - The Almost Total Loss of Acropora palmata from Shallow Waters off Barbados, West Indies, Initiated by Catastrophic Destruction of a Major Bank-Barrier Reef off the Southeast Coast.
  
• Thomas J. Casadevall, U.S. Geological Survey, Denver, Colorado - Lusi: Long-lived Mud Eruption near Surabaya, Indonesia.

John Wesley Powell Auditorium, Cosmos Club
2170 Florida Ave NW
Washington, D.C.

Refreshments 7:30 pm; Meeting 8:00

Future meetings 2009: April 22 (Bradley Lecture); Sept. 23; Oct. 14; Nov. 4; Dec. 9.

Labels: environmental, fish, gsw, meetings, mining, reefs, volcano

Nevada's Yucca Mountain site for a proposed nuclear waste repository has lost much of its funding in President Obama's proposed budget. Personally, I think this is a good call - I never thought that the Yucca Mountain site seemed viable for the geological long-term. For a facility being designed to outlast human civilization (warning signs are not written in English, but in sign language that's predicted to still be useful when potential meddlers show up 10,000 years from now), Yucca Mountain is located in too tectonically-active an area for my liking. Basin and Range extension, with associated earthquakes and volcanism, imperils the facility's security over the long-term.

But then where do we put this nuclear waste? We've got more and more of it every day. I'm a fan of nuclear energy because I feel that in spite of the risks associated with radioactive leaks, it's a proven technology that looks better all the time because it produces no carbon emissions. To me, the relatively short-term (local) risk of radiation leaks is outweighed by CO2's long-term (global) risk of climate change. Provided sufficient security, I think it's a great "halfway house" between fossil fuels and 'alternative' energies like solar, wind, and geothermal.

Yucca Mountain has several advantages in terms of its location: it's dry, and it's not in someone's backyard (far from large populations -- though Los Vegas residents might quibble with the definition of "far"). But Nevada's regular seismic shaking (3rd in rank among the U.S. states, after California and Alaska) and the proximity of some young volcanic extrusions make me think it's not so great a spot if you want the waste to stay put. I'm thinking that the best place for nuclear waste would be in the craton, the stable interior of the continent. I'm thinking: Canadian Shield, maybe in Minnesota or Michigan or Wisconsin. The issue there is water: you would be trading tectonic stability for saturation and precipitation.

I'll readily admit I'm not an expert here -- just a geologist speculating on an issue that's more complex than mere geology. What do you think? Where's the best place to store nuclear waste until radioactive decay makes it reasonably safe? Use 10,000 years as your hypothetical timeline, bearing in mind how different the world is today than it was 10,000 years ago.

Labels: CO2, earthquakes, energy, environmental, michigan, minnesota, nevada, volcano, wisconsin

For the penultimate post in my Ecuador travel series, I hereby recount the story of climbing the mountain called Iliniza Norte (16,997 feet above sea level: the tallest peak I've ever summitted).

We began by driving up from the town of Chaupi, where we were staying at a hostel, to the trailhead above treeline in the paramo ecosystem...


We had hoped for awesome weather, but as with our previous peak bagging in Ecuador, the clouds were here too, making a ceiling that we headed up into...




Heading up into the clouds; the valley below fades away...


...and we start to see snow.






We went up a long, steep snowfield for probably two hours... It was frustrating going: take one step forward, slide two steps backward. The snow got thicker and thicker...

Eventually, when we got close to the summit, we got off the snowfield and onto some rocks. I was surprised to feel how my energy spiked at the prospect of rock-scrambling. The long slog up the snowfield was boring and repetitive, but this was totally engaging as a physical/mental workout. Here's Lily and Diego climbing up:



At the summit, there's a steel cross with various doodads attached...


This is the highest point above sea level I've ever experienced. When I stood on the summit, my head was above 17,000 feet in elevation!



Silly video of the summit team making celebratory noises:


Then Diego said, "I think we go down now, because of thunders."

The guy knows his stuff: as soon as he had said this, we heard a ba-boom from off in the white clouds somewhere... Yikes. Okay, time to head down.

Descending the rocks:


When we got to the snowfield, another peal of thunder sounded, and this one was louder than the first one. The snowfield, fortunately, made for easy going -- we essentially skied down it. It was pretty exciting... Flashes of lightning, booms of thunder (sometimes within a microsecond of one another), adrenaline pumping, running/sliding/skiing downhill as fast as we could.

We did not get hit by lightning.

After we got below cloud level (and into a valley where we felt a little less exposed to lightning strikes), we could see that the lower elevations had gotten some frozen precipitation too: a mix of snow and hail:











When we got back to the vehicle, we found it covered in hail:


Now for the adventure after the adventure: driving down a steep, twisting, muddy mountain road that's coated with hail and host to numerous roaring streams of runoff. It was almost as intense as descending the snowfield amid lightning bolts: the vehicle slid and knocked against a mud embankment at one point, and it was all seriously sketchy. Diego said he had never seen anything like it.

Here's some video of a raging torrent of meltwater/runoff flowing over a road surface that's decorated with white hailstones:



We did not crash the car.

Back safely at the hostel, we took hot showers and drank beer and congratulated ourselves for clearly being such daring adventurers. Whew... the next morning, we took our weary selves back to Quito.

One more Ecuador post to go... on lichens... stay tuned.

Labels: ecuador, ice, mountains, snow, south america, travel, volcano

As you'll recall, when I left off with my Ecuadorian travelouge, Lily and I had summited Pasochoa, and then taken a day-hike in Cotopaxi National Park. Next up, a new mountain that has about the same elevation as Mt. Whitney (highest peak in the lower 48 United States): about 14,500 feet. To climb this extinct volcano called Ruminahui (Roo-min-ya-wee), we headed up a ridge between two adjacent glacially-carved valleys.















Me with clouds and background glacial valley:


Diego (our guide) on the trail:


Up on top, there was less vegetation, but more cloud... and snow was falling.

The bedrock was a volcanic breccia that had been cut by numerous andesitic dikes:






You can see some blurry snowflakes in the previous photo. Here's a cold-looking Lily with her boots on an andesitic dike:



Here's a couple of close-ups to show the cross-cutting relationships between the andesite dikes and the volcanic breccia:





Here's a short, not-especially-great video wherein I point out a few things that don't really show up all that well. Still, you get to see it snowing!

A big "thanks" to NOVA's king of digital video, Richard Attix, who helped me rotate this video and crop out some unintended footage from the raw video we shot on the mountain that day.

Cold hikers:



"Sheesh! It's cold up here!":



On the way down, we also took some time to check out the plants. Here's one called "Orejas de conejo" ("Ears of the rabbit"):

Here's one that smells exactly like chocolate!


In fact, Lily was able to harvest this chocolate bar from it!

Okay, not really. It's money that grows on trees, not chocolate bars.

So that's the story of our second successful summit... now there was only one more to go... the legendary Iliniza Norte. Photos from that hike in a couple of days...

Labels: ecuador, glacial landforms, mountains, plants, sediment, south america, travel, volcano

We now return you to our originally-scheduled photo-travelogue...

On the second day of our Andean mountain tour in Ecuador, Lily and I set out from Tambopaxi Lodge, our comfortable accomodation in Cotopaxi National Park:



We were going for a day-hike, checking out the scenery with our guide Diego while we acclimatized for some more serious mountain climbing in the days to come. The official goal of our hike was to check out two naturally-flowing cold springs, where the agua was pura, and safe to drink. Here's the first one, issuing from the base of a lava flow, with me awkwardly twisting around to raise a bottle of the good stuff:



Spring #2, of greater volume:


Some shots of the scenery:







The extinct volcano Sincholagua:


Me with Sincholagua (and lower cloud cover) in the distance:

A look back at Pasochoa, which we had climbed the day before:


And Cotopaxi itself, the charismatic, active volcano which draws most people to the park:


Critters:

A big insect, maybe a grylloblattid?


Feral horses:


We also saw some cool "primitive" plants (plants with ancient lineages):

Liverworts:


Sphenopsids:


Club mosses:


There was also some geology going on...

Here's a handful of loose lapilli (mixed in with some organics):


Stream deposits on the flanks of Cotopaxi Volcano, showing different water energy regimes. The coarsest layer in the middle represents the fastest moving water (capable of carrying larger particles of sediment):


And here's some flow-banding in andesite:


It started raining on our way back to the lodge, but that was okay, because hot showers and warm tea awaited there. Acclimatization, check! Next up, the peak known as Ruminahui...

Labels: arthropods, critters, ecuador, geology, mammals, plants, south america, travel, volcano

I went to Ecuador to climb mountains.

After a lovely two days of recovery in the thermal springs of Papallacta, Lily and I began our mountain-climbing tour. We summited three peaks in the central Ecuadorian Andes: Pasochoa, Ruminahui, and Iliniza Norte. Today I'd like to share our experiences climbing the first (and shortest) of those, the peak called Pasochoa. Here it is from the rough road we drove in on:



From a Google Maps perspective, here's the physiography of the surrounding area. Pasochoa is the highest peak of the central volcano in this view:



Once we started hiking, we got above the trees and into the paramo ecosystem, a high-elevation grassland biome that exists between treeline and the bare rocks above where only lichens survive. Another view of the peak, which is about 13,700 feet in elevation:



Once we got up a little bit, we could look down to the Valle de los Chillos, a massive valley between Andean peaks, south of Quito:



One of the most spectacular things that happened on this hike is we saw an Andean condor, which flew by between us and this view, quite spectacularly. We weren't able to get the camera out in time to capture it, but with its black and white plumage, it was unmistakeable. Here's a amateurish Photoshop to show what it kind of looked like:



I pointed out the volcanic breccia to Lily and our guide, Diego:



More of the same could be seen in eroded-out minarets on the flanks of the mountain:




Pasochoa is one tall bit along the rim of a much larger caldera, and when we got up to the edge of that caldera, we got a real sense of its sudden drop-off. Clouds/fog curled up and over the lip, obscuring the view, but we could peer down into them and see that the land dropped steeply away for many hundreds of feet.



Lily gives a sense of scale to the edge of the caldera:



After lunch on top, more clouds moved in, and we decided to decamp back to the vehicle. Here's Diego and I descending the trail towards lower elevations.



Being a guy who had just recently recovered from something akin to pneumonia, I felt pretty good about making the summit of a 13,700' peak. Next up: let's see if we can't find something a little bit taller...

Labels: birdies, ecuador, mountains, south america, travel, volcano

Here's a pretty cool outcrop I found as we were leaving Cotopaxi National Park in Ecuador (in early January). I've got two small photos taken laterally on different parts of the outcrop (exposed by a stream), and then I follow those with two close-up crops, showing the details. I've posted the full-size versions of the first two photos on Flickr, so you can click through if you want more details. The zoomed-in shots are displayed here at the same size you'll find on Flickr.





What's going on here? It looks like we've got a series of thinner, relatively fine-grained layers below, topped off with a massive, poorly-sorted layer. The lower layers are all ash- and lapilli-sized grains, each stratum pretty well sorted. The upper layer consists of all kinds of different-sized chunks, including some boulders, "floating" in a really fine-grained matrix. Check it out:





I interpret this as a series of volcanic ash-(& lapilli-)falls that were then buried beneath a lahar, a volcanic mudflow. The lahar's slurry-like consistency was capable of transporting really large clasts, and when it slowed down, it set up like nature's concrete.

I think this is pretty spectacular stuff.

Labels: ecuador, igneous, mass wasting, south america, stratigraphy, travel, volcano

The perpetually-interesting site Oddee hosted a series of satellite images of the Earth today, including this one from April of last year. Somehow I missed it then...

The image, originally from NASA's Earth Observatory (one of the finest websites I know of for those interested in Earth science), shows a collection of volcanoes in the western Arabian Peninsula. A large version of the image (unlabeled) is here.

The most spectacular thing about this image is the color contrast between the volcanoes on the left versus the volcanoes on the right. This spectacular contrast is indicative of the rock types involved in each volcano. On the left, felsic lava was erupting, which cooled into the extrusive rock rhyolite. On the right, mafic lava was erupting, which cooled into the extrusive rock basalt. Mafic igneous rocks like basalt have a higher proportion of the elements iron, magnesium, and calcium as compared to elements like silicon, potassium, and sodium. Felsic igneous rocks are, in a sense, distillates of mafic source rocks: they are made of minerals that are more easily melted.

Also worth noting is the way the basalt overlaps the rhyolite between Jabal Bayda' and Jabal Abyad tells us that the rhyolite came first, and the basalt came second, an example of relative dating. And these insights can be gleaned from space... or more accurately, from our computer screens, depicting an image from space. That's pretty incredible, when you think about it.

FYI, here's what NASA's William Stefanov wrote as the caption for this exceptional image:

The western half of the Arabian Peninsula contains not only large expanses of sand and gravel, but extensive lava fields known as haraat (harrat for a named field). One such field is the 14,000-square-kilometer Harrat Khaybar, located approximately 137 kilometers to the northeast of the city of Al Madinah (Medina). The volcanic field was formed by eruptions along a 100-kilometer, north-south vent system over the past 5 million years. The most recent recorded eruption took place between 600-700 AD.

Harrat Khaybar contains a wide range of volcanic rock types and spectacular landforms, several of which are represented in this astronaut photograph. Jabal ("mountain" in Arabic) al Qidr is built from several generations of dark, fluid basalt lava flows. Jabal Abyad, in the center of the image, was formed from a more viscous, silica-rich lava classified as a rhyolite. While the 322-meter high Jabal al Qidr exhibits the textbook cone shape of a stratovolcano, Jabal Abyad is a lava dome; a rounded mass of thicker, more solidified lava flows. To the west (image top center) is the impressive Jabal Bayda'. This symmetric structure is a tuff cone, formed by eruption of lava in the presence of water. The combination produces wet, sticky pyroclastic deposits that can build a steep cone structure, particularly if the deposits consolidate quickly.

White deposits visible in the crater of Jabal Bayda' and two other locations to the south are sand and silt that accumulate in shallow, protected depressions. The tuff cones in the Harrat Khaybar suggest that the local climate was much wetter during some periods of volcanic activity. Today, however, the regional climate is hyperarid - little to no yearly precipitation - leading to an almost total lack of vegetation.

Labels: basalt, blogs, igneous, middle east, satellite imagery, volcano, websites

What's the tallest mountain on Earth? Most would say Everest, since it's the highest point above sea level. I mentioned this issue as part of my lead-in to my Mauna Kea post, since some folks might claim Mauna Kea as the tallest, since it rises the most above its base on the oceanic crust of the Pacific Plate. But there's a third contender: Mount Chimborazo, in Ecuador.

The planet Earth is not a perfect sphere; it bulges a bit at the equator (about 13 miles) compared to the poles. The result is that if you look at two mountains of exactly the same elevation, one located at the pole and one at the equator, the equatorial one will be 13 miles further away from the center of the Earth than the polar one. That makes the peak of the tallest equatorial mountain (Chimborazo is at ~1.5 degrees south) the point on Earth that is furthest away from the center of the planet. It is 1.3 miles (2.1 km) further away from the center of the Earth than the summit of Everest is. NPR covered this surprising statistic in an entertaining piece in 2007. However, as the commenter on this post-NPR post notes, it's not just the silicate earth that bulges at the equator, it's the atmosphere, too. So it's not like the air is thinner at Chimborazo than Everest. You may be closer to the Moon atop Chimborazo, but you're not closer to "space" due to all that extra thick atmosphere above your head.

Here's a Google Maps "terrain view" map of Chimborazo (high relief peak east of El Arenal):


I had hoped to "auto-post" this while I'm traveling in Ecuador, for about the same time I would be looking at Chimborazo with my own eyes. However, I got sick over the holidays, and the persistent illness forced me to change my travel plans. I'll still be going to Ecuador -- but only for one week instead of the planned two. And I still hope to catch a glimpse of Mount Chimborazo. Hopefully when I get back to DC, I'll be able to share some photos of this superlative mountain. For now, the map will have to do.

Labels: ecuador, maps, mountains, south america, travel, volcano

A high-definition eruption video is giving clues to how volcanoes work, as reported by WIRED magazine staff attending last week's AGU meeting. Turns out WIRED actually had a big AGU coverage site, which I only just noticed. Some good stuff there, though. Check it out.

Labels: agu, meetings, movies, volcano, websites

Holy lava, geoblogosphere!

On my recent trip to Hawai'i, I saw a variety of different kinds of holes in the basaltic "lava rock" that makes up the majority of the island. The largest examples were lava tubes, like the Thurston Lava Tube near Kilauea Iki in Hawai'i Volcanoes National Park:

This is a conduit through which molten lava once flowed. Once the source of that lava ceased producing, though, the lava drained out and the tube was left empty, like a cave. (Caves, of course, are holes produced through an entirely different process.) The ceiling of this lava tube is about twenty feet high.

Not too far distant, there's a nice area where you can see tree molds:


These are holes left in the rock as the lava flowed around a tree. The heat of the molten rock burst the tree's cells, releasing water and quenching the lava in a cylindrical tube around the tree. The dewatered tree then burned up, leaving a hollow mold showing the shape of its (former) trunk:


The holes are kinda deep:


Inside the tree mold, you can see the texture of the (in this case, pahoehoe) lava that flowed around the tree trunk:


Looking up the invisible tree trunk, and out the hole towards Lily:


Here's a bigger hole, the Halema'uma'u Crater within Kilauea Caldera:

It's venting a lot of steam, hydrogen sulfide, and other gases.

Google Map for reference on how this hole relates to the even bigger hole that is the caldera:


The photo of Halema'uma'u above was taken from the Hawai'i Volcano Observatory adjacent to the Jagger Museum in the park. Stepping back a bit from the window, you can see that I'm not the only one taking this particular photo... This is the same spot where the Halema'uma'u Crater webcam is filmed. That's what all these cameras are doing in the foreground:


Janet Babb took some time out of her day to show us around the place (thanks, Janet!), and I made sure to sign into the guest book. There, I was pleased to see past visitors, including (I think) Ron Schott's crew from Fort Hays State University Lake Superior State University, the William and Mary crew, and most recently, the NOVA crew headed by my colleagues Ken Rasmussen and Nancy Chamberlain:


Janet let me hold a chunk of recently erupted basalt. This one erupted in early October, I think she said. It was about a month old when I held it -- that's my record for a really recent rock:

As noted in a previous post, this vesicular texture displayed by this sample is one more example of (smaller) holes in lava.

Labels: basalt, hawaii, travel, volcano

What's the tallest mountain on Earth?

Everest, right? Well, yeah: if you're measuring from sea level. If you're measuring from the top of the crust the mountain rises from though, it's Mauna Kea, Hawai'i. It's about ~13,800 feet above sea level, but it rises ~33,500 feet from the oceanic crust to the peak (that's compared to Everest's mere ~29,000 feet from base to peak. So... you could say that Mauna Kea is the tallest mountain on our planet... (you could!)

On Thanksgiving day, my friend Lily and I took a drive up to the top of Mauna Kea, and did a little hike up there at high elevation. Today, I'd like to share some photographs of that excursion. We saw some pretty cool geology.

On the drive up the mountain, we saw an animal which was apropos, considering the day:

Gobble, gobble, gobble. Watch out turkeys, we'll be back after we work up an appetite...

Here's Lily's jeep in the "saddle" between Mauna Kea and Mauna Loa, looking north (with Mauna Kea in the background and basaltic lava flows from Mauna Loa in the foreground):


Some cider cones (the Hawai'ian word for cinder cone is pu'u) in the saddle:


Turning the other way (looking south), you can see the bulky form of "the long mountain," Mauna Loa. What a classic shield volcano shape! I love the fact that it's so dang wide it makes a lousy photograph. You just can't capture its spread-out bulk in a photo; it's too massive:


This was the spot where I pretended to have my toes overrun by a pahoehoe flow:


As we drove up the road to the top of the mountain, I was amazed at the raw volcanic landscape, decorated with cinder cones like this one:


At one point, we passed a neat little angular unconformity on the roadside. Here it is, with a nickel (white dot left of center) for scale:


Here's a closer-shot of this small angular unconformity. Earlier layers of ash and lapilli were deposited at a steep angle, and then eroded (perhaps by glaciation? pure speculation there) before more ash and lapilli were deposited atop it, at a lower angle. There's not likely to be much time missing here, and so perhaps it's better to think of this as the top of a cross-bed, an advancing front of pyroclastic deposition moving down the mountainside, overrun by later eruptions, which may have scoured off the upper few inches (??? pure speculation) or so before deposition.

Really, the truncated tops of cross-beds are mini-angular-unconformities, when you think about it; just not with the same amount of time missing at a "real" angular unconformity (with millions of years missing) due to mountain building like the one at Siccar Point. (Video of cross-beds forming)

Here's something else which the clueless geologist might mistake for a sign of mountain building:
No, those aren't originally-horizontal strata that have later been folded. They're layers (again of ash and lapilli) deposited on the originally-rough topography of the mountainside, covering small ridges and filling small valleys. Where a given layer is exposed at higher elevation, I interpret to be a paleo-topographic high; where that same stratum is exposed at lower elevation, that's a paleo-topographic low. The roadcut reveals these layers have undulating shapes, but this is unlikely to be folding that results from tectonic compression: instead, I think it's showing us the lay of the ancient land surface.

Looking south, we could see past Mauna Loa to the actively erupting steam vent coming out of Halemaumau Crater at Kilauea Caldera (source of the vog!):


Near the summit of Mauna Kea, there are a bunch of astronomical observatories:






On the summit is where you find those examples I mentioned the other day of hawaiite, a rock of basaltic composition that is very dense (ostensibly due to erupting beneath the extra pressures of a Pleistocene ice cap):


Here's me on the summit:


View to the north from the summit: More cinder cones...


Here's a YouTube video of me pointing stuff out from the summit (Kilauea, Hualalai, Mauna Loa, observatories, hikers, etc.). Unfortunately the wind makes it all but unintelligable, but I filmed it, doggone it, so I'm going to post it:



I found a beautiful example of a volcanic bomb up there:


After the visit to the summit, we went for a hike to a small supposedly-glacially-gouged-out lake below the summit (Lake Waiau):


Here's a Google Map, showing the lake's location:


I was surprised to see a thick biofilm on the bottom of the lake:


Encrusting the pebbles and cobbles there, it reminded me of Nora Noffke's modern and Archean biofilm photos in the recent GSA Today, as well as my "Life in Extreme Environments" class this past summer at Montana State University.


We saw some nice examples of structural geology on this hike. Previously, I've mentioned plumose structure, a branching pattern on the topography of fracture surfaces in fine-grained rocks. We saw some of that on blocks of basalt atop Mauna Kea, as in this example (again a repeat photo, but the other day I showed it to you for the vesicle; today I'm showing it to you for the plumose structure.)


A similar feature are arrest lines, which again are minute variations in the surface of a fracture. Like plumose structure, which branches from a source point (where the fracture initiated) and branches out in the direction of propagation, arrest lines tell us about the development of a joint. Unlike plumose structure, though, they are not parallel to the propagating fracture front. Instead, they form perpendicular to it, and record how the fracture propagates in small "steps." Each of these arrest lines is interpreted as being a spot where the fracture grew a little bit, then stopped ("arrested") and then grew some more. In this case, the fracture face we're looking at started at the bottom of the picture and grew towards the top of the photo. You can even see some less-discernible plumose structure backing this up:

Similar arrest lines can be seen in basalt images here and here...

We also saw some pretty spectacular xenoliths. Here's one of gabbro in basalt:


Here's one of peridotite in basalt:


And a few more:



My boots, with another volcanic bomb:


Driving back down the mountain afterwards, we got this nice view of the cinder cones (pu'us!) in the eastern part of the "saddle" between Maunas Kea and Loa:


This Mauna Kea excursion was one of my favorite things that I did on my all-too-brief trip to Hawaii. It was great to get up in the high country, where the air is thin (and vog free!) and the skies are deep blue, and the geology is surprisingly varied (at least it was surprising to me, and pleasantly so). The hike let us work up a good appetite, so we headed back down the mountain and straight to Thanksgiving dinner!

Labels: basalt, birdies, geology, glacial landforms, hawaii, igneous, mountains, msse, primary structures, structure, travel, unconformities, volcano, xenoliths

This is what I saw upon waking in Hapuna Beach State Park, my first morning on the big island:

Labels: hawaii, sun, volcano

Contrary to what you may have heard, it's not all basalt. Even the basalt is astonishingly varied: the extrusive rock of a thousand faces... Here I'll share some pictures I took of rocks in Hawai'i:

There's pahoehoe:


...and there's a'a:


Here's a pahoehoe flow oozing over my boot (just kidding; it was cold when I did this):


Pahoehoe lobes can drain out, leaving only the outer skin as rock, but with a hollow center. These are lava tubes (nickel for scale):


Another one (nickel for scale):


Cool texture on the inside of this lava tube (nickel for scale):

...and zooming in a bit closer (it looks like wrinkled cellophane!):


A stack of cross-sectioned pahoehoe flows, showing their tubular (totally tubular, dude) shape:


Some Hawai'i basalt is massive, like this cobble...


...or like this cobble of hawaiite, a dense form of basalt found atop Mauna Kea (where it apparently erupted beneath Pleistocene ice caps):


But the majority of Hawai'i's basalts are vesicular, meaning they contain "Swiss Cheese" type holes that result from gas bubbles. When the lava erupts, it experiences less pressure at the Earth's surface than it was subjected to at depth. As a result, many gases (steam, CO2, sulfur dioxide, chlorine, argon, others) exsolve from the lava solution and make bubbles. If these bubbles don't get a chance to pop before the lava sets up into igneous rock, then they are preserved as vesicles. Sometimes the vesicles are small:


...and sometimes they are big:


Sometimes, they are really big. Here's one I could fit my entire Nalgene water bottle into:


When vesicles later get filled in with mineral deposits, we call them amygdules. Here's some vesicles that have gotten a light coat of a white mineral on their interiors: the first step to converting a vesicle into an amygdule:


Some of the vesicles show strain (almost certainly due to late-stage flow in the increasingly-viscous lava, getting stretched out like air bubbles in pouring honey). Surface tension on the bubble wants to make it spherical, and the lower the lava's viscosity, the easier it will be to attain that perfect spherical shape, minimizing the surface-area-to-volume ratio. So when we find them in cigar-shapes or pancake-shapes instead, that's a clue that they've been deformed. Deformed not by tectonic forces (ductile flow at depth in an orogen), but ductile flow as a result of their formation, in a sluggishly oozing blob of lava:


Another example of stretched-out vesicles:


A lonely vesicle in an otherwise massive basalt:


Not sure what's going on here, but it looks cool (popped vesicles in sticky lava?):


Another thing you see a lot of in these Hawai'ian basalts are phenocrysts of certain minerals. Here, for instance, is a cobble showing nice olivine phenocrysts:


...and another:


Here's one I showed you last week when we discussed Green Sands Beach:


Here's an outcrop which shows phenocrysts of plagioclase feldspar instead:


And a river cobble (also vesicular) bearing a healthy population of feldspar phenocrysts:


Holy feldspar, Batman! This rock has a huge proportion of feldspars (you'll note that it's still vesicular, though: in spite of the overwhelming volume of macroscopic crystals, this is still an extrusive rock):


Here's something else caught up in a finer grained (and yes, vesicular) basaltic matrix: another piece of basalt!

This is a xenolith of slightly-older basalt showing flow banding in its own trains of vesicles, that after solidification got broken off and included in younger flows of basalt. I'll post some additional xenolith photos later this week.

It's not all basalt, though. Here's a breccia made of basaltic cobbles (penny for scale):


And a closer shot of the same outcrop (penny for scale):


Finally, a rock I was surprised to see: an intermediate-composition extrusive igneous rock called benmoreite (nickel for scale, and note the rock hammer impact marks):


Benmoreite is way more felsic that anything else on the island. According to my volcanic advisor Jess, it's the result of late-stage partial melting of basaltic source rocks in the island's oldest volcano, Kohala. In other words, it's a distillation of basalt: concentrating the most felsic components in this decidedly-lighter-complected rock (nickel for scale):

Labels: basalt, geology, hawaii, igneous, national parks, pleistocene, primary structures, volcano, xenoliths

I had planned to write about vog next week, but NASA's Earth Observatory has forced my hand this morning by publishing this:

What you see in this image of the Hawaiian islands is a lot of vog, an acrid mix of sulfur dioxide, water, and oxygen that results when volcanic emissions mix with the atmosphere.

When I was there last week, I experienced some vog, starting with the source. Here's Halema'uma'u Crater (part of Kilauea Caldera), steaming away in Hawai'i Volcanoes National Park, spewing water vapor, carbon dioxide, sulfur dioxide, and other gaseous goodies upward and downwind:

The prevailing winds keep these nasty gases close to the ground west of the crater, resulting in the park service closing down the roads in that area of the park.

From there, the gases drift west and north, mixing and interacting with the atmosphere, forming vog. If the trade winds aren't active, the vog kind of stalls on the western side of the big island, and even drifts along the archipelago to plague Maui and the other islands.

On Thanksgiving day, I was standing on top of Mauna Kea, one of the five volcanoes that makes up the island, and on the descent back down the mountain, looking south towards Mauna Loa, where I could see a curtain of vog on the western flank of the big mountain (obscuring Kona and the coast):


Now here's a zoomed-in shot, augmented with a dotted line to show you approximately where the silhouette of Mauna Loa would be, if you could see it through all the vog there on the western side of the mountain. Honestly, it looked just like a curtain of greyish white hanging from the sky: palpable and with a discrete edge:


Down in the thick of it:


It wasn't as noxious as I thought to be in it and breathe it, but the vog definitely had a distinct scent and taste, and my eyes were watery (though that may have been psychosomatic, because it was kind of freaky how thick it was).

According to my friend Lily in Waimea, the trade winds have picked up in the past day or so, though, and scrubbed away the vog. So: clear skies return to Hawai'i... but for how long?

Labels: clouds, geology, hawaii, national parks, travel, volcano

I'm on the big island of Hawai'i for the Thanksgiving break; and I've really enjoyed trooping around and checking out the volcanic features. (Photos once I get back to DC...) The other night I saw Bela Fleck and the Flecktones perform in Waimea, and they were playing lots of Christmas tunes from their brilliant new album. The next day, hiking on Mauna Kea, the residual music mixed in my brain with the cool igneous geology I was seeing. The result? The Twelve Days of Volcanoes... Enjoy!

On the first day of Christmas my island sent to me:
a bunch of pahoehoe

On the second day of Christmas my island sent to me:
2 Pele's hairs
and a bunch of pahoehoe

On the third day of Christmas my island sent to me:
3 aa's
2 Pele's hairs
and a bunch of pahoehoe

On the fourth day of Christmas my island sent to me:
4 falling blocks
3 aa's
2 Pele's hairs
and a bunch of pahoehoe

On the fifth day of Christmas my island sent to me:
5 volcanoes
4 falling blocks
3 aa's
2 Pele's hairs
and a bunch of pahoehoe

On the sixth day of Christmas my island sent to me:
6 basalts flowing
5 volcanoes
4 falling blocks
3 aa's
2 Pele's hairs
and a bunch of pahoehoe

On the seventh day of Christmas my island sent to me:
7 tubes of lava
6 basalts flowing
5 volcanoes
4 falling blocks
3 aa's
2 Pele's hairs
and a bunch of pahoehoe

On the eighth day of Christmas my island sent to me:
8 steam explosions
7 tubes of lava
6 basalts flowing
5 volcanoes
4 falling blocks
3 aa's
2 Pele's hairs
and a bunch of pahoehoe

On the ninth day of Christmas my island sent to me:
9 green sand beaches
8 steam explosions
7 tubes of lava
6 basalts flowing
5 volcanoes
4 falling blocks
3 aa's
2 Pele's hairs
and a bunch of pahoehoe

On the tenth day of Christmas my island sent to me:
10 billion vesicles
9 green sand beaches
8 steam explosions
7 tubes of lava
6 basalts flowing
5 volcanoes
4 falling blocks
3 aa's
2 Pele's hairs
and a bunch of pahoehoe

On the eleventh day of Christmas my island sent to me:
11 craters glowing
10 billion vesicles
9 green sand beaches
8 steam explosions
7 tubes of lava
6 basalts flowing
5 volcanoes
4 falling blocks
3 aa's
2 Pele's hairs
and a bunch of pahoehoe

On the twelfth day of Christmas my island sent to me:
12 voggy lungfuls
11 craters glowing
10 billion vesicles
9 green sand beaches
8 steam explosions
7 tubes of lava
6 basalts flowing
5 volcanoes
4 falling blocks
3 aa's
2 Pele's hairs
and a bunch of pahoehoe

Labels: basalt, hawaii, humor, music, travel, volcano

Beautiful. Hat tip to Unexpected Entropy.

Labels: blogs, volcano

Two weeks ago, my friend Lily took a hike up Mauna Loa. Lily teaches science at a middle school on the big island of Hawaii, and we became friends this summer at MSSE Dino Camp. I would think that living on the island of Hawaii would have some major disadvantages over time (my guess is that I'd get cabin fever living on an island), but you can also imagine that it would have some major advantages too.

In addition to live volcanic activity, surfing, exotic birds, and just general paradise-like conditions, add this to the list: climbing a tropical volcano to see giant frost crystals forming on top! Here's an image she took at sunrise, looking west over the summit caldera:



Mauna Loa is the largest volcano on the planet Earth. Rising 5 kilometers from the Pacific seafloor to sea level, then an additional 4 kilometers to its summit, Mauna Loa has an estimated volume of 80,000 cubic kilometers! It's big.

Because it's so tall, the weather at the top is much colder than the tropical sultriness at the beachfront resorts. Lily and her hiking partner found this out when they camped out on top, and woke to find that overnight, giant crystals of frost had grown spike-like from the tops of the exposed cobbles and boulders of basalt. I don't have a sense of scale here, but I'm guessing these are a centimeter tall or so... Here's a close-up of the lower-left corner of the upper image:



Pretty cool, eh? Literally. Maybe Hawaii has more variety than I had assumed. I think this calls for a field trip to investigate!

Thanks to Lil for sharing the photo!

Labels: hawaii, ice, volcano

Sorry for the long delay in posting here. Turns out they don't have Wi-Fi at Phantom Ranch.

After my time in Zion (did Angels Landing and a few other small hikes while there), I scooted down to Las Vegas, Nevada, to pick up my father and two brothers. They had flown in there, and after one day were already tired of the city. I was ready to leave five minutes after I got there, which is always how I feel about Vegas. Somehow, circumstances keep conspiring to bring me back there, though...

We drove out of the Basin & Range and up onto the Colorado Plateau, and spent the night at Cliff Dwellers, a lodge near Marble Canyon. I was really impressed with their food and drink. We had an amazing meal, washed down with several pitchers of Newcastle Brown Ale! In the morning, we gathered up our gear and put onto the river. Our trip consisted of two rafts outfitted with side tubes and motors and guides. One raft was entirely made up of a family from Charlotte, North Carolina, including the glass artist Wayland Cato, III. The Bentley's raft was augmented by a family from Littleton, Colorado, two oil men from Oklahoma, and a couple of veteran river rafters from northern California. It was a motley crew, but we started having fun immediately.

We launched at Lees Ferry, in the Kaibab Limestone, and then descended in both elevation and geologic time. At our first lunch stop, in the Coconino Formation, I was astonished at several synapsid reptile trackways protruding from the underside of the paleo-dune slipfaces overhead. I took some photos, but because of the aforementioned software issue, I won't be able to share them until I get back to DC in August. As the first couple of days went by, we just went deeper and deeper into the Paleozoic stratigraphy of the Colorado Plateau. Of all the formations, my favorite was the Bright Angel Shale, which has many beautiful colors in thin layers throughout (not to mention oodles of trace fossils). I was particularly pleased to play frisbee in a "cave" in the Redwall Limestone, a place that I have shown photographs of to my students, but never actually seen before. It's a HUGE cliff of the Redwall, and then this seemingly small cave etched into its base (and filled with sand), but the cave could easily swallow my building at NOVA: it's big!

At some point, we crossed a major fault, and were instantly dropped down about a billion years in geologic time. Once we got into the Grand Canyon Supergroup and the metamorphic and igneous basement rocks, my geologic interest really went wah-wah. The Vishnu Schist and Zoroaster Granite make a stunning contrast: really beautiful pink cutting across dark grey. I introduced my raft-mates to the idea of the Mazatzal Orogeny, and we discussed how boudinage forms. There were faults and folds galore: structural paradise. I loved it.

Did I mention the rapids? There were rapids. The water was COLD, thanks to Glen Canyon Dam(n). But the sun was hot, and we dried out quickly. Meals were gourmet, though the campsites were spartan (you had to poop in a box that got packed onto the raft each morning: leave no trace!). We slept out under the stars every night, sometimes dealing with blowing sand.

We took several hikes up side canyons to see waterfalls and go swimming. Several of these were good and physically challenging, which is what I wanted. I enjoyed swimming and playing "three-dimensional frisbee" in Havasu Creek, and doing cannonball jumps in the weird blue of the Little Colorado River.

The final day on the river, we came to the western section of the Canyon where recent lava flows (basalt) have cascaded over the rim and down into the canyon. This is famous for producing one of the toughest rapids in the whole Grand Canyon: Lava Falls. But it was awesome to float by and see umpteen gazillion columnar joints, and whole feeder canyons plugged up by basalt. Pretty cool!

Our final morning, we were helicoptered out of the Canyon to a ranch on the rim. This was my first time in a helicopter, and it was giddy and amazing. I want to fly! From the ranch, we transferred to small fixed-wing planes, and I said goodbye to my family. They went back to Vegas, and I flew back to Cliff Dwellers, where my Prius (and a shower!) awaited.

Labels: fossils, geology, grand canyon, minerals, primary structures, rivers, sediment, travel, volcano

Check out these amazing images of the ashy flood deposits from Chaiten volcano that have buried Chaiten town. The Volcanism Blog, by the way, is extremely consistent in quality and focus, and I tip my hat to them for doing such a great job. If you haven't already discovered that site, you should spend some time checking out their other posts too.

Labels: blogs, south america, volcano

And here's the view hiking back down the canyon to the car:

It's a classic U-shaped valley, the signature of alpine glacial topography. Here's the Google Maps "terrain" view of this valley:

View Larger Map

Labels: glacial landforms, montana, volcano

Last night I attended my first meeting of the Potomac Geophysical Society (PGS). The PGS meets on Thursday nights, and I usually can't make it because I teach on Thursday nights. (I do however attend meetings of the Geological Society of Washington quite regularly, but those are on Wednesday nights.) Now that the semester is over, I was able to make it to the final PGS meeting of the spring.

The meeting was held at Fort Meyer Officer's Club. It's on a military base adjacent to Arlington National Cemetery, and before entering, my Prius had to be searched for bombs (as did all other civilian vehicles). The Officer's Club was about what you would expect, I guess -- kind of 1950's decor, elegant once. I noticed they had compact fluorescent light bulbs in all the sockets, which pleased me. PGS meetings consist of: (1) beer downstairs in the lounge, (2) dinner upstairs in the "Campaign Room," (3) business details, and (4) a talk by a guest speaker.

Last night's speaker was Bill Burton, from the USGS's volcano hazards and monitoring program. Bill's office will be launching a comprehensive new volcano website later this year, and he gave us a brief preview of its features in last night's talk. If you'd like a look for yourself, they have a beta version of the site online now.

Labels: gsw, meetings, pgs, volcano, websites

Holy cow! Chaiten is continuing to erupt, and witnesses are posting some incredible photographs of the event.

I highly recommend you check out these two sites, which I am only aware of thanks to James Annan who posted the links at his Empty Blog.

Seriously: check them out. It's like Independence Day down there.

Labels: news, south america, volcano

Whoa! Chaiten volcano in Chile has been erupting for a few days. It's a big'un: Argentina's getting some ash from its extrusive neighbor. Check out the coverage on the volcanism blog, or via NASA's Earth Observatory. UPDATE: also from the volcanism blog.

Labels: south america, volcano

Just got through watching an episode of the PBS program NOVA (which I like to refer to as the "other" NOVA). The episode was titled "Volcano under the city," and it looks at the volcano Nyiragongo in Congo, central Africa. This was the same volcano that had such a spectacular eruption in 2002, when lava flowed through the city of Goma, on the shore of Lake Kivu. The program follows UN vulcanologist Jacques Durieux on a journey through Goma and into Nyiragongo to evaluate the risk for the ~2 million people who live in the mountain's shadow. The program explores volcanic hazards including lava flows, landslides, lake overturn (a la Lake Nyos), and pockets of CO2 in low-lying areas on land. This last one provided what I found to be the most dramatic footage: Durieux tosses a signal flare into one of the ditches, and the smoke rises and flows on top of the invisible layer of CO2 below: it demonstrates dramatically how there's something invisible pooled in that ditch due to its density. There's also plenty of footage of frothing spewing blobby lava, if that's your thing. As is often the case, the narrator overpitches the dangerous aspects of the situation, and the whole hour-long show feels kind of like a hyped-up movie trailer. Certainly the situation there is dangerous, but I feel like some credibility gets lost when every word is uttered with a sense of looming menace.

Labels: africa, CO2, movies, tv, volcano

Last night at the meeting of the Geological Society of Washington, we were treated to a couple of really entertaining talks. The first was by John Eichelberger, of the U.S. Geological Survey in Reston (formerly of UAF). John is interested in Plinian eruptions -- the ones where volcanoes shoot massive amounts of ash and gas upwards in an eruption column. He made the point that while Plinian eruptions are widely characterized as "explosive," they are actually a steady state phenomenon with a high volume, "like a firehose."

Labels: gsw, volcano

It's funny how one thing leads to another. In promoting our Climate Change Symposium on Friday, I wrote to Cerphe (pronounced "Surf"), probably the best DJ in the world, who's on air in the afternoons on 94.7 The Globe, our DC-area "world-class rock" station that also features a green message. Cerphe wrote back, saying he'd get some mentions on the air this week, and also mentioned that his wife has a small business building green homes. I noticed that the business is headquartered in Bentonville, Virginia, out in the Shenandoah Valley between Massanutten Mountain and the Blue Ridge. And it occurred to me that I've looked at a bentonite layer out there in the Valley (see photo), not too far away from Bentonville. Bentonite is a common clay mineral that in stratigraphic layers is usually interpreted as weathered volcanic ash. (The one pictured above is possibly the "Big Bentonite" that accompanied the onset of the Ordovician Taconian Orogeny in eastern North America.) Could it be that bentonite is named for Bentonville, Virginia? Well, Wikipedia tells me that "The absorbent clay was given the name bentonite by an American geologist sometime after its discovery in about 1890 ...after the Benton Formation in Montana's Rock Creek area." So that took me to the entry on Fort Benton, Montana, which was named for the first 5-term U.S. Senator, Thomas Hart Benton. He was an advocate of westward expansion by the United States, the idea that later was dubbed "Manifest Destiny." So: as near as I can follow, bentonite is a mineral named for a place, which is in turn named for a man. What this has to do with world-class rock and climate change is anybody's guess.

Labels: appalachians, history, montana, volcano

It appears that researchers have located a volcano under a thick mantle of Antarctic ice. They found the volcano's approximate position by mapping a layer of ash and glass shards within the glacial ice. The volcano erupted in or around 325 B.C., say Hugh Corr and David Vaughan, based on their study. (Both men work for the British Antarctic Survey.)

They initially detected the layer of volcanic debris through airborne radar-reflectance measurements. (At first they thought the reflective layer was the bedrock at the bottom of the ice, since it provided such a strong reflection.) Then they looked at the thickness of snow overlying this layer and correlated the ash deposit with eruption-linked acid-rich snow strata in ice cores that were taken in adjacent areas. The image here shows the radar-wave reflectance profile.

(According to my rough calculations, the vertical exaggeration of the cross-section is about 6x. )

This has been billed as the first time we've seen clear evidence of a volcano pushing its way up through the ice sheet in Antarctica, though similar eruptions have been observed in historical times in Iceland (like Grimsvotn in 2004). However, just this past weekend I watched an episode of the PBS series NOVA, which showed scientists working on a big ice coring project near what they interpreted to be a sub-ice volcano. There was a big depression, and ice was flowing into the depression (downhill) from all directions. Ergo that ice had to be going somewhere. NOVA's scientists posited it was being melted, and that meltwater was greasing the skids of the bottom of multiple ice streams which were cruising out of that area of the ice sheet. (These ice streams are just faster-flowing areas of the ice sheet, like currents zooming through ocean water, sometimes 50x as fast as the "background" rate of flow.)

The show got me thinking about another study, coincidentally also published in Nature Geoscience, although this one was in the inaugural January issue. It's a study of the Kennicott Glacier, in Alaska's Wrangell-St. Elias National Park:

The study was conducted by three researchers, all associated with the Institute of Arctic and Alpine Research: Timothy Bartholomaus, Robert Anderson & Suzanne Anderson. They measured a bunch of variables on the Kennicott Glacier, seeing which of them correlated with a rise in the glacier's speed. They found that an annual flood event from Hidden Creek Lake (HCL in part d of the diagram, orange line) occurred at the same time as the glacier's maximum speeds during the measured interval, the maximum discharge of the (downstream) Kennicott River, and a maximum electrical conductivity of the water in the Kennicott River (the bedrock beneath the glacier is halite-bearing). As this whopper of a graphic shows, Not only does the glacier speed up its horizontal motion during the flood (part b), but the whole thing actually rises up vertically too! (part c) Also, Donoho Falls Lake (DHL in part d of the diagram, blue line) downstream experiences a huge surge in water as the flood passes over it. Conductivity spikes during this same interval. Bartholomaus and the two Andersons propose that when the ice dam of the lake gives way and all that water surges into the glacier's channel, it overwhelms the capacity of the sub-glacial network of channels & raises the pore pressure of water within the ice. This extra pressure "inflates" the space between glacial ice & underlying bedrock, and the whole thing slides like an air hockey puck. At least, as long as the super-high pressure lasts. Once the flood ebbs, pore pressure in the glacier drops back down to levels that are easily counteracted by friction. The glacier slows once more to a "normal" pace.

This is very reminiscent to me of studies done on how an increase in pore pressure along a fault plane can trigger movement along that fault. When I took structural geology in college, the professor described an example from Colorado (I think) where the Army (I think) was injecting nerve gas down into the ground to get rid of it. The nasty nerve gas was dissolved in water, and the periodic injections of this solution correlated with a series of earthquakes (movement) along a previously-unknown subterranean fault. The injections increased fluid pressure in the pore space of the rock, and that "inflated" the space between the fault blocks, and the relatively minor shear acting on them was then enough to get the two to slide. I won't get into the whole Mohr Circle here, but I do recommend you check out the famous Beer Can Experiment to get an idea of how an increase in fluid pressure can cause an otherwise "stuck" fault to slide. Anyhow, I guess the base of a glacier is essentially a big fault, with one kind of rock below and another (ice) above. Same phenomenon, in other words, but different geologic context.

The Bartholomaus + 2 Andersons study also has some big global warming implications. The recent surge noted in Greenland's glaciers (e.g. Zwally, et al., 2002) may be explained by higher rates of surface melting (due to elevated Arctic air temperatures) which then produces lots of meltwater, which flows down through the glaciers to the bottom via meltwater channels which plunge through the ice. Via the mechanism explained above, the great ice sheet atop Greenland is reduced more rapidly than without the surface melting. One of these meltwater channels was featured prominently on the cover of the June 2007 issue of National Geographic.

So, with that, I think I'll end this blog post -- my thoughts went from volcanoes to ice streams & subglacial meltwater to fault slippage to global warming. I reckon that's just about enough... just about... but I also noticed something else...

A tangent about publication: The Corr & Vaughan findings will be published in the second issue of the new spinoff journal Nature Geoscience, but they were posted online over the weekend in advance of the actual print publication of that issue. An article in the New York Times alerted me to the study. I'm not surprised that Nature, like the Proceedings of the Royal Society, has taken to hatching specialty sub-journals to convey more articles each month. (An "about the journal" page appears on their website, if you're curious.) The image shown here with this post is from the Times, not the actual Nature Geoscience article.

References:
Hugh F. J. Corr & David G. Vaughan. (2008) "A recent volcanic eruption beneath the West Antarctic ice sheet." Nature Geoscience. Published online: 20 Jan. 2008. doi:10.1038/ngeo106

Timothy C. Bartholomaus, Robert S. Anderson & Suzanne P. Anderson. (2008) "Response of glacier basal motion to transient water storage." Nature Geoscience 1, 33-37. Published online: 20 December 2007 doi:10.1038/ngeo.2007.52

H. Jay Zwally, Waleed Abdalati, Tom Herring, Kristine Larson, Jack Saba, & Konrad Steffen. (2002) "Surface melt-induced acceleration of Greenland Ice-Sheet flow." Science 297, 218-222. doi: 10.1126/science.1072708

Also see:
Kenneth Chang. "Scientists find active volcano in Antarctica." The New York Times. Published online: 21 Jan. 2008.

Labels: antarctica, global warming, tv, volcano

Geological travels in Northern Ireland, part II:

Mammatus clouds hanging over Lough Erne, in western Northern Ireland. Our friends Jodie and Rory have a caravan on this large lake. After our tour of the cathedrals of Armagh, Jodie drove us out here to have a hike at the lake (which was great in spite of ending in darkness and rain) and to rest up in their modish accomodations there.













This is Mount Slemish, an eroded volcanic neck in Northern Ireland near Antrim. This "basalt plug" was once the center of a volcano which erupted lava all over this vicinity. Because the massive basalt in the volcano's "throat" was tougher than the surrounding stratified rock layers, it stood up strongly to erosion, and now rises to 1,457 feet (437 m) in elevation, dominating the local landscape.

Labels: clouds, northern ireland, slemish, volcano