NOVA Geoblog

New geoblog: Bloc de Camp

2010-02-08T15:51:00.003-05:00

Just got a note about a two-year-old blog about geology that has so far escaped my attention (and possibly also the attention of the curator of the geoblogosphere, Robert Huber?) Bloc de camp (Catalan for "Field Notebook") is a blog dedicated to the geological heritage of Catalonia (country around Barcelona, northeastern Iberian Peninsula). It can be read in Catalan, Spanish and English. They are also on Facebook.

Upcoming changes

2010-02-08T08:46:00.003-05:00

Thanks to the 64 of you who have already completed the survey which accompanied the thousandth post here. The survey is intended for ALL readers of this blog, no matter who you are. So if you haven't yet shared your feedback, please do so now. I'll close the survey on Friday morning. I really am interested in your perspective. There are some major changes in the works for this blog, and I've already gotten some terrific ideas from the survey responses.

I'll announce the changes sometime next week... after I've heard from everyone who has something to say.

Snowtographs

2010-02-07T12:59:00.001-05:00

You may have heard that D.C. got some snow this weekend. (It's true.) We went for a walk this morning to check out what the snowed-in city looked like. Here are a few photos...

This is fun:

K Street, home of the lobbyists:

Group of robins hanging out at National Geographic HQ:

The White House gets whiter:

A magnolia tree in Jackson Square, not doing so well:

(Magnolias seem particularly susceptible to losing limbs via heavy snow...)

Photogenic trees:

Washington Monument:

Up-side-down Diplocraterion? Or just where someone sat in the snow?

This trace fossil is more obvious; Bicyclus, clearly:

The National Mall (Smithsonian's Natural History Museum at left, Capitol Building at right):

Doppelganger week for the Capitol:

Cold Triceratops:

Snow decorates the trees in front of the FBI building:

Pennsylvania Avenue:

Callan checks on the snow depth:

Guess this roof isn't very well insulated...

Some structures... Here's a set of two normal faults in a snow stratum atop a hedge:

(Glove for scale, of course.) Here's a different angle on these extensional structures:

(Because GMU classes were canceled on Friday, I assigned my structural geology students to make some structures in the snow -- like Kim's example, perhaps, or perhaps like this hedge, but really limited only by their own imaginations...)

Here's a different one:

That's a sheet of snow being driven downward by gravity, sliding over a roof (fault-like) but then arching up at the tip (this would look 'antiform' if it were rotated 90 degrees...). Kind of like a compressional antiform transitioning into a thrust fault, a common 'structural ingredient' in fold and thrust belts the world over.

Some more normal faults, including en echelon arrays like we saw last September in the volcanic tableland north of Bishop, California... These are viewed from the bottom -- they are forming in snow atop the glass roof of the pagoda-thingy that covers the Columbia Heights metro escalators. Notice too the color difference (due to more or less snow) from the peak of the pagoda (where the faults are -- an area of "crustal" thinning) to the bottom (where the snow is thickest).

Finally, if you haven't already seen it, check out this time-lapse image of the snow accumulating! And here's one from Greg Willis, who has shared videos on this blog before... Enjoy!

Stay warm out there, everyone...

Two books about evolution

2010-02-06T07:24:00.001-05:00

Book Month continues...

Why Evolution Is True - Jerry Coyne

I already mentioned one of the three great books about evolution that came out recently: Your Inner Fish, by Neil Shubin*. I heartily recommend pairing Fish with WEIT, as they have some overlap in content and style. This is an easily-accessible review of the most important (and compelling) bits that pile up in support of the idea that evolution has occurred over time, and that natural selection is its principle driver. It's full of interesting facts that are clear refutations of the idea of divine creation of all species from separate starting points in the recent geological past. FYI, Coyne is also a blogger: he writes semi-daily at the blog Why Evolution Is True (shocking title, eh?).

The Greatest Show on Earth - Richard Dawkins

Richard Dawkins gets plenty of press time for his athiest viewpoint, and he's written a book about that, too (which I haven't read). As a result, many theists probably won't want to touch any of his other tomes with a ten-foot pole. But I assure you, that would be a huge mistake when it comes to The Greatest Show on Earth: this is an amazing, rich, awesome book. It demolishes the notion of a young Earth and special creation with a treasure trove of information about biological systems. More importantly, it celebrates the beauty of evolution: Dawkin's delight in the various evolved solutions to the problems of living is evident. Like luciferin, it shines from the page. The way I see it, Why Evolution Is True and Your Inner Fish play the part of "executive summaries," while The Greatest Show on Earth is the juicy, complicated, tangled jungle of evolutionary explanation. It's great. While it lacks the quality of being concise, Dawkins' erudition and clear-mindedness more than make up for it. Consider Coyne's WEIT as your appetizer, but save Dawkins for the main course.
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* By the way, Neil Shubin has posted PowerPoint slideshows of the images in each chapter of Your Inner Fish for use by educators teaching about evolution. Check them out. Unfortunately, there are a substantial number of spelling errors in the captions to these images, but the images themselves could be quite useful to anyone wanting to incorporate an 'evo-devo' element into Historical Geology or Paleontology.

"Reading the Rocks" by Marcia Bjornerud

2010-02-05T07:33:00.002-05:00

Book Month continues...

I recently read the excellent book Reading the Rocks, by Marcia Bjornerud. I would recommend this book to anyone interested in their planet. I think it's an equally good choice for professionals and interested amateurs. The book works on several levels. It's lyrically written, with an economy of flourishes, but an ear for a good turn of phrase. She's also really keen on analogies, and that makes me like her a lot. Finally, she seems to be a kindred spirit, using geological insight as a gateway to philosophical perspective. The book is rich in detail, though broad enough in scope that it will satisfy a structural geologist, an astronomer, or your average run-of-the-mill nature lover.

A taste of her style:

"Human consciousness is arguably the first truly novel innovation to arise since Cambrian time, in the sense that the technologies our consciousness has spawned have freed us from the limits of our own body architecture." (p. 172)

"Over more than 4 billion years, in beach sand, volcanic glass, granites, and garnet schists, the planet has unintentionally kept a rich and idiosyncratic journal of its past.... The genre varies from breathless thriller to quotidian diary; the action ranges from microbial metabolisms to mountain building." (p. 5)

Under a section subtitled "Grammar and Syntax of the Three Rock Languages," Bjornerud says, "Just as you wouldn't look to a cookbook for information on military history, you wouldn't expect a sandstone to tell you much about the Earth's interior. Sedimentary rocks are the best reference works to consult if you are interested in past conditions at the surface of the Earth - for example, ancient climates, biological activity, or the distribution of water bodies. Igneous rocks chronicle the long-term chemical evolution of the Earth and provide glimpses into processes that occur at inaccessible depths. Metamorphic rocks, born in one setting (sedimentary or igneous) and transformed as they encounter new environments, are the travel writers of the rock world, chronicling their astounding journeys through the crust." (p. 33)

I love how she gives anthropomorphic personalities to rocks. This is her great talent as a writer. Along similar lines as the quote above, she later compares mafic to felsic igneous rocks: "A mafic rock like basalt generally has tales to tell of life in the mantle, while for a felsic rock like granite, whose progenitors were themselves crustal, the mantle is a nearly forgotten ancestral homeland." (p. 43)

She has a great analogy for radioactive decay, using "parent" and "daughter" as part of the analogy itself: A "magnanimous parent who transfers half of his savings to his daughter each year on her birthday." Each year, the parent has less money, but the daughter's wealth has grown by exactly that same amount. "At any time, an external auditor could determine the age of the girl - the number of years the parent had been giving money to her - by finding the ratio of the amount in the daughter's account to the amount in the father's account." (p. 58) Clever!

She gives some great comparisons for viscosity, including glacial ice, basaltic lava, rhyolitic lava, motor oil, water at room temperature, and blood (which she helpfully reminds us is thicker than water).

Chapter 3 concludes with a great comparison between the small and the large: "...Small phenomena can wield surprising power: A trivial deviation from sphericity causes the entire planet to wobble, raindrops and tiny flaws in minerals bring down mountains, trace gases in the air govern climate, and microbes modulate the atmosphere. Perhaps the greatest challenge we face in attempting to fathom the Earth is to gain a proper sense of our own size as a human species; like spoiled children, we routinely overstimate our importance on the planet but underestimate the destructiveness of our self-absorption." (p.98)

Criticism:

The "currently accepted geologic timescale" at the beginning of the book includes "Tertiary," with no mention of Paleogene or Neogene. Frowny face.

She attributes John Playfair's quote about being "giddy from peering into the abyss of time" directly to James Hutton. Tragically, Hutton was never so eloquent himself.

Overall: Highly recommended. Get it; read it.

Icy volcanic breccia

2010-02-04T16:56:00.008-05:00

This is beautiful: That's an image by Chris Waythomas of the USGS, hosted by the Alaska Volcano Observatory website. It shows a cutbank (river-eroded alluvium deposit) along Rust Slough, south of the Drift River Oil Terminal, northeast of Redoubt Volcano. The sediments exposed were deposited on March 22, 2009 by a lahar (volcanic mudflow). The lahar deposit is 2.5 m thick. When I saw this image tonight (as I was searching for another shot), I was particularly struck by the subrounded clasts of ice in the mud. Here is ice acting the part that chunks of rock usually play. Technically, ice is a mineral, and so these chunks are sedimentary clasts much like any other... But to me there's something distinctly different about seeing ice cobbles and pebbles included in a sedimentary deposit. On a planet as warm as Earth, this sort of thing isn't likely to be preserved in the geologic record. It would melt! ...And that gets me thinking about other planets and planet-like objects, like Titan. The Huygens probe took pictures of sedimentary clasts, presumably of ice, on the surface of that moon. Other cold locations could have CO2 ice ("dry ice"): That makes for the sort of rock specimen that would be really difficult to keep on your shelf as a 'deskcrop'...

An additional thought: how could the former presence of icy clasts have influenced the geologic record? Perhaps ice clasts were an integral part of a deposit as it was laid down... but then later the ice melts away. How could we detect and control for this?

Sierra Nevada geologic map repository

2010-02-04T06:32:00.002-05:00

Wow. Here's a great resource for those who do research in the Sierras, or the geologically-inclined visitor. Making this available online is a terrific public service by Allen Glazner and Mike Oksin at UNC-Chapel Hill.

Via Geology News' automated reposting of "geology" items from del.icio.us.

Congratulations to Michael Welland!

2010-02-03T08:19:00.003-05:00

The word is out: Michael Welland, author of Sand: the Never-ending Story and Monday's guest blogger here, is being honored. Sand has been awarded the 2009 John Burroughs Medal, which puts Michael in extremely esteemed company: John McPhee, Gary Paul Nabhan, William Beebe, Edwin Way Teale, Aldo Leopold, Roger Tory Peterson, Barry Lopez, and David Quammen are among the luminaries who have earned this award. Well done, Michael! You make us proud.

I can't wait to see what this guy writes next...

"Cataclysm" by Doug Huigen

2010-02-03T07:44:00.003-05:00

I mentioned in Monday's Sand post that this was "book month" here at NOVA Geoblog. That means it's now time for a quick book review of CATACLYSM: When Human Stories Meet Earth's Faults, by Douglas W. Huigen...

When I was writing my Benchmarks piece for EARTH magazine about the Hebgen Lake earthquake and the Madison River landslide, I spoke on the phone to Doug Huigen, who was then just finishing a multiyear project learning about the geology of the Hebgen Lake area, and interviewing survivors of the event. He was very genial and shared some great information when we spoke.

Later in the year, my summer Rockies field course brought me out to the site of the landslide itself. Here's me and my students at the Earthquake Lake Visitors' Center, talking about the structure of the mountain behind us, and why it failed almost fifty years previously:

After I was done pontificating, we went inside and watched the compelling movie they show there, and then I noticed that Doug's book was for sale on the counter. I bought a copy.

Months later, I finally found the time to read it. For some reason, though, I've found it difficult to finish up with my "book review" blog posts. I started this one in late October, for instance. I'm hoping that by declaring February to be "book month," I can motivate myself to crank through these reviews.

Cataclysm is a nice introduction to the events of August 1959, viewed both through the people on the ground experiencing the earthquake and landslide, and through the perspective of modern-day geological insight. Huigen spoke to a great many survivors of the event, and relates their stories with compassion and an ear for colloquial language. The book is subdivided into three main sections: (1) stories of people during the event, (2) a bunch of photographs and graphics showing the area, the people, and the geology, and (3) a description of the geology underlying the earthquake and landslide. The story is very compelling, and I think it's worth reading this book if you're going to be visiting the Hebgen Lake landslide site.

The book is self-published by Huigen, so there's some issues with typos and formatting of photo annotations, but I guess that could also be seen as part of its charm. It's an excellent repository of a lot of information, and I learned some new things by reading it. I was particularly pleased with the image Huigen has on the inside of the front cover: a sketch of the major geological features in the area. The inside of the back cover is a gorgeous geologic map of the same terrain, but Huigen didn't include the map's explanation, so you have no idea what the various rock units actually are (unless you're already familiar with the area).

Bottom line: not the most amazing piece of literature in the universe, but an important compilation of data about the Hebgen Lake earthquake and landslide: data both of the geologic variety and the 'oral history' variety. I'm glad I read it.

Your Sand questions answered

2010-02-01T07:33:00.044-05:00

Today we have a special post here at NOVA Geoblog. Author Michael Welland joins us to answer a bevy of questions about the topic of his expertise: sand. Michael's book Sand: The Never-Ending Story is now out in paperback, and this post is one stop on his "virtual book tour" through the geoblogosphere. I really enjoyed reading Sand, and I reviewed it last year in EARTH magazine (hardcopy only, I'm afraid: no link possible). I was tickled to see that a quote was mined from my EARTH review for the back cover of the paperback edition of the book, a first for me.

If you have a sand question to ask, leave it in the comments, and Michael can respond there, too.

This post also serves to kick off "Book Month" here at NOVA Geoblog. All this month, I'll be blogging about the books that I have read recently.

All questions in this post come from my spring 2010 Physical Geology students. Enjoy! -CB

What are people who collect sand as a hobby called?

"Odd!" ...They are also often called arenophiles, "sand lovers" but strictly, that's a mixture of Latin and Greek - "arena" is the Latin for sand. To be consistently Greek, they should be "psammophiles" but then that term tends to be used by biologists and botanists to describe critters and plants that live in the sand.

How come sand gets everywhere when you go to the beach? And by everywhere, I mean everywhere...sealed Ziploc bags, inside cell phones, places you don't want it...everywhere. Or, on a more scientific sounding note-beaches that are eroding. Is it due to sand being swept out by the ocean waves faster than it can be replaced? (How is sand formed?) If that's the case-why do some beaches erode faster than other? Is it because of the width between the dunes(?) and the ocean?

Boy, do I know about sand getting everywhere! After my Sahara travels, my backpack pockets still contain sand, my camera zoom makes uncomfortable grating noises, and I had a hell of a time explaining to my cellphone company why there were sand grains under the keys (I'd stupidly used its calculator for map scale conversions when we were trying to figure out where we were). I guess this problem is just another of the strange behaviors of granular materials in that size range.

Now, as for beaches, they are just about the most dynamic environments on earth, changing every day, with the seasons, with every storm, and with changing sea levels. Check out the story of the wholesale move of the Cape Hatteras Lighthouse. Every beach has a sediment budget - incomings and outgoings that constantly change. Sand is added to the beach (but also carried away) by longshore drift and by the action of every wave. A storm will erode unimaginable amounts of sand - which is then deposited elsewhere. Sand blows off the beach and onto the dunes, or off the dunes and onto the beach - an incredibly complex system. Typically, at certain points along a coast sand will be swept into the head of a submarine canyon and flushed out into the deep sea - essentially never to return (check out, for example, the Monterey Submarine Canyon).

Here are a couple of interesting photos of where sand ended up after Hurricane Katrina:

And here are three photos of Dauphin Island, Alabama, before Hurricane Ivan, after it, and after Hurricane Katrina - spot the differences!

Over the course of several thousand years, can a black sandy beach turn into a white sandy beach? I have heard about green sand. Is green sand existent and where can you find it? What elements is sand made out of ? ...And why does its color change in other places?

In talking about the definition of sand in terms of size rather than composition, and the different types of sand, I've begun to answer these questions. Just as the cuisine of a local restaurant is dominated by local ingredients, so is the composition of a sand in any one place. You wouldn't expect to find beaches of coral fragments in Greenland, or sand grains of old metamorphic rocks in Hawaii. The sands of a particular beach may have been carried a long distance by rivers and coastal currents, but they originate from the same system, a system that is stable over long periods of time. The river and beach sands of the east coast of the US tell the story of the erosion of the Appalachians and the effects of the Ice Ages. So no, a black sandy beach will not turn into a white sandy beach over the course of a few thousand years - but if, over the course of a longer period of time, different source rocks are exposed in the areas where the sand grains originate, or if there is a major reorganization of sand-transporting currents, then the beach composition will change to reflect that. We see this all the time in the geological record - changes in sand composition that tell us about changes in provenance, tectonic activity and so on.

But then, as I was writing this, I suddenly remembered an example of a black beach turning into a normal beach - overnight! If you go to any beach and look at the ripples in the sand, there will generally be smears of dark-colored grains emphasizing the forms of the ripples. These are grains of heavier minerals, often iron oxides, which are winnowed by the action of waves because of their weight. If this winnowing, by waves, currents, or rivers, takes place over a long period of time, then considerable concentrations of heavy minerals can result; these deposits, called placers, can be commercially important and are the sources of diamonds, gold and many other important mineral commodities. But on a beach, just as easily as such a deposit can form, so can it be removed by a storm; I described an example of this in the book:

...such an occurrence was the cause of one of Thomas Edison's many business failures. On a fishing trip with friends off the coast of Long Island, Edison put into shore for lunch and found the beach covered with a layer of black sand. He took some home and discovered that the black grains were a magnetic iron oxide mineral - magnetite - which stuck to a magnet while the common sand grains fell off. Edison's enthusiasm ran, as it often did, ahead of his business sense, and he immediately arranged for the purchase of the beach and the manufacture of separating machinery. Unfortunately, by the time he and his colleagues returned to Long Island, a winter storm had reworked the beach and completely removed the black sand.

So there's a case of a black sand beach disappearing!

Green sand - yes, it exists, most famously on Hawaii. Local ingredients again, the volcanic rocks contain crystals of the apple-green mineral olivine, and this can become concentrated on some beaches to become the main constituent of the sand - placers again. Here's an example from the Big Island:

Sand comes from sediments that are carried down from rivers that come from mountains. So is sand a mixture of minerals and dirt? ...Or just a lot of different broken down minerals? I just watched something about China's issue with being continuously battered by massive sandstorms. What I want to know is: Where is the sand coming from? Why is it hitting China, and what are the health risks/other consequences of these sandstorms?

The breakdown of rocks by chemical and physical weathering and the transport of the debris by rivers is the most common origin of sand - but it's not the only one. Beaches in the tropics are made of sand that is biological in origin - shell fragments, bits of coral, and the shells of minute organisms. Which brings us to a key point: Sand is defined purely by size.

This is for a very good reason - granular materials that fall in this size range behave very differently from things smaller and things bigger. And those behaviours are often bizarre. It really doesn't matter what the sand is made of, its composition. And note that, reflecting the fact that nature works in multiples, each category is twice the size range of the next smaller one. So, it doesn't matter if the material is made up of 1 mm quartz grains, shells, diamonds - or sugar - technically it's coarse sand. It can be made up purely of quartz or purely of foraminifera shells, or a mixture of minerals and rock fragments, or a mixture of coral and shell fragments - it's all sand. Some beaches in the tropics are made up almost entirely of sand-sized pellets of dried fish shit.
Dirt is the non-technical (and mostly American) term for soil, and soil is the in situ material that results from the conspiracy of chemical and physical weathering and organic material and activity. Once it's eroded and transported by wind or water, it isn't dirt any more. So, technically, the dirt in much of Nebraska is sand (the Sand Hills support only very poor vegetation); once the dunes become active again (perhaps as a result of changing climate) that sand will be on the move once more.
And that's a big part of what's happening in China. More than 2.5 million square kilometres (a million square miles - more than four times the area of Texas) of the country is desert, and so sand and dust storms have always been a problem. But poor land management on a massive scale - removal of forests, over-grazing, and soil-depleting agriculture - has made the problem worse. What had been stable soil, dirt, is now exposed to the winds and on the move - very much like the dustbowl conditions of the American Midwest in the 1930s. The total area of China's deserts is growing at around 200 square kilometers (80 sq mi) every month, and every year tens of thousands of tons of sand and dust are blown into Beijing. China's capital has always suffered from dust storms, helped again by the ice age, when grinding glaciers wore rocks down to flour, technically known as loess, which, once airborne, blankets huge areas for long periods of time. But Beijing's dust storms are turning into sandstorms. It's not necessary to travel to the Gobi Desert to find encroaching sand; it's a mere hour's drive out of Beijing. The Great Wall, built to defend against invaders from the west, is proving no match for the onslaught of sand: whole sections are being destroyed by the storms.

So the sand is coming from the interior deserts, but more and more from degraded landscapes that are newly becoming desert. The problems for homes and infrastructure are enormous, but so are the health risks in populated areas from particulates - hence the dramatic measures taken at the time of the Beijing Olympics.

How come there is so much sand on the shores and coastlines of the earth, and absolutely none as you move toward the middle of a country or continent?

Don't tell the residents of Nebraska that - a quarter of their state is covered in sand dunes! The Sand Hills are the largest area of dunes in the western hemisphere, covering 60,000 square kilometres and were active and mobile between 1000 and 1200 CE. They were formed originally from the debris of the glacial erosion of the Rocky Mountains. The hills were stabilized eight hundred years ago but have had episodes of reincarnation since: a long drought toward the end of the eighteenth century resuscitated dunes on the Great Plains, whose activity caused problems for the westbound wagon trains decades later.

You can find more imagery and information here. And think about the great active deserts of the world where huge amounts of sand are to be found - the Sahara, the Arabian Peninsula, essentially the entire interior of Australia, a quarter of the land area of China. But it's not just the deserts - every river bank and lake shore has sand. About the only places on the earth's surface where sand is rare are the very deep ocean floors - and it's rare but not absent. Sand can be dropped from melting icebergs and flushed out into the deep oceans by the tremendous energy of turbidity currents, slurries of water and sediment hurtling down the continental slopes and spreading out across the deep ocean floors; any of the great deep ocean currents can move sand around - and they do. And there are countless sand grains in your back yard, mixed up in the soil.

Here's a Google Earth image of Nebraska:

Hoping this question related enough to sand, because I'm still under the impression that all/most glass is made of sand. I've heard that in stained glass windows inside ancient churches, there is a "bulge" at the bottom of the glass, and that because of its disorderly atomic structure, gravity can "pull" it down a bit after hundreds of years. I've also heard that this is totally wrong, and that the bulge is just an effect of the way they made stained glass at the time. I'd love it if your friend could shed some light on the issue.

It's an old and common "urban myth." Although glass does flow, the timescale over which it happens is far too long for even the oldest windows to show any effect. Old methods of making glass did not create perfect sheets and, logically, if a piece is thicker at one end than the other, you would install the thick end at the base of the window. There's a good article about the myth on Corning's website.

What makes quicksand so powerful that it can drag a human down?

Another "urban myth!" There's a great episode of Mythbusters that examines "killer quicksand" and has them bobbing around in a giant tub of quicksand, trying to be sucked in. They bust the myth: "Quicksand is denser than water; the greater the density, the greater the buoyancy of objects within. Any victims found in quicksand likely died for some other reason (i.e. exposure to the elements)." You can watch the episode here.
Quicksand is an example of one of the strange behaviours of sand-sized granular materials - dilatancy. Here's a bit about this from the book:
Quicksand forms when there is sufficient water in between the grains to separate them - to push them apart through dilatancy - but the water is prevented from draining; the sand is in suspension. This can happen when an incoming tide scours large holes in the sand that are rapidly filled by the outgoing tide, trapping water and air in the sand. Or a subsurface spring or other source of water percolates upward through a body of sand, dilating it. The result is a slurry, delicately balanced between solid and liquid, switching instantly but briefly between the two states with the slightest disturbance. But being a mix of water and sand, quicksand is more dense than water, and the human body floats well in it. The problem arises when a person floating in quicksand tries to move too quickly; the movement destroys the dilatancy of the slurry and the grains reconvene and jam back into a solid, effectively cementing the unfortunate person in place. It has been estimated that the force needed to pull your foot out of jammed quicksand is about that needed to lift a medium-sized car. The key is to wiggle, allowing water to fill the space created around you, and then swim, very slowly. Quicksand is lethal because lone individuals die of exposure, starve, or drown when the tide comes in, not because they are sucked under.

What is the calculated estimate of the amount of sand on Earth?

Essentially impossible to calculate - particularly if you include all the sand grains in ancient sandstones. But that hasn't stopped people having a stab at it. I wrote a bit about this in the book:
In 1980, Carl Sagan, the enthusiastic popularizer of all things astronomical, kicked off one of the most enduring, entertaining, but quantitatively pointless debates about large numbers. He declared, in his television series Cosmos, that "the total number of stars in the universe is larger than all the grains of sand on all the beaches of the planet Earth." The calculations are ongoing and the debate rumbles on, particularly in the ethereal realms of the internet, and there are, predictably, two schools of thought. While estimates are always increasing, the number of stars is the easier number to calculate: anywhere between 1020 and 1022. As for the grains of sand - well, it depends. What are the assumptions in terms of grain size and, indeed, what counts as a beach? Only the areas of sand above high tide, or areas underwater as well? Depending on how you choose to do the calculation, you can derive a number that is larger or smaller than 1022. And if all the sand grains of the Earth are included, not just those on beaches, then it's again a different matter.

Is sand from different places unique enough for someone to determine where it came from?

Absolutely - to the extent that sand stuck under a vehicle or in the sole of a shoe can and is used in criminal forensics. Simplest if I quote the section on this from the book:
With the sophisticated microscopic diagnostics now possible, the character of soil and sand as evidence in a wide variety of criminal cases has taken on increasing significance. There are crimes that rarely make the headlines, such as cactus smuggling, that can be routinely solved by being able to point to the origin of sand clinging to the roots of the contraband. Investment scams where evidence for a new gold prospect is "salted" with grains of gold from elsewhere can be uncovered by a microscopic look at those grains.
A significant amount of the world's gold supplies comes from the sands of ancient and modern rivers. In 1997 a shipment of these grains of gold worth $3 million was made from mines in the interior of Ghana to the coast and then on to London for processing. After a dispute over the arrangements and cost, the shipment was moved on to Canada via Amsterdam. Canada was the first place where the crates were tagged and given new seals. When they were eventually opened, they contained ordinary sand and iron bars. Where on the shipment's circuitous route had the substitution taken place? The sand was examined by Richard Munroe, a Canadian forensic geologist and policeman. If the substitution had been made in London or Amsterdam, the sand would likely bear the imprint of its northern European origins - particularly the action of ice from the glaciers that had so recently sculpted the continent. But none of those signs were there. Instead, the grains bore the distinctive features of being subjected to a tropical climate, and their composition was typical of the geology of the interior of Ghana. While local security difficulties prohibited making an exact match of the sand grains, any Canadian involvement was ruled out and the insurance claim filed by the mining company was dropped. Sand is a popular material in crimes of "substitution"; in the lively commerce between North and South America, sand has been substituted for, among other goods, cigarettes going south and perfume going north. The genetic fingerprint of the sand involved has pinpointed the location of the crime and helped prove innocence and guilt.
Sand and soil found in the soles of shoes, on clothing, or on tires can place people or vehicles in a particular place - however much they may deny it. Geology has become a standard tool in the kit of government forensic laboratories the world over, but it has been around for some time. The fictional Sherlock Holmes claimed to be able to describe an itinerary from mud splashes on trousers. In real life, evidence from sand has been used for over a hundred years. In 1908, in Bavaria, a poacher was suspected of murdering a young woman. His wife had cleaned his shoes the day before the murder, but they now had three layers of sand and soil stuck on their soles. As part of the investigation, one Georg Popp, a local chemist, applied his geological expertise to these layers. He reasoned that the layer next to the sole of the shoe was the oldest; it was made of the same materials as those outside the suspect's house. The second layer contained red sand and other materials identical to those from where the body had been found. The last and most recent layer contained brick fragments, cement, and coal dust that matched samples from where the suspect's gun had been found. What this layer did not match was the soil from the fields where the suspect claimed to have been walking at the time of the murder. The prosecution case was complete.
On a dark, rainy night in September 2002, a black truck parked beside the Shenandoah River in Virginia. Another truck pulled up, and the window rolled down to reveal the barrel of a shotgun. The driver of the first truck was killed at point-blank range. The murderer left in a hurry, the wheels of his truck spinning in the sand and gravel. After a preliminary investigation, the police had a suspect but insufficient evidence to prove guilt. When the suspect was seen starting to wash his red pickup truck, the police swooped. The truck was spattered with fresh mud: time to bring in the forensic geologists. The mud contained some very distinctive sand grains, a variety of minerals that could only have come from a local quarry. While the quarry was not where the murder had taken place, water washed debris from the quarry into the river, which carried it downstream, mixing and diluting it with the other sand and mud in the river. At low water levels, these were dumped in sandbanks along the river's edge. Geological sleuthing demonstrated that each successive sandbar downstream from the quarry contained less and less quarry debris, and the only one that precisely matched the material from the suspect's pickup was the scene of the murder. The suspect pled guilty in the face of this incontrovertible evidence.
Forensic geology has played a part in a wide range of criminal cases worldwide, but perhaps the most high-profile, yet disappointing, example was the murder of the Italian prime minister Aldo Moro. In May 1978, the body of the kidnapped prime minister was found in a car in Rome. Sand from his clothes and shoes, and from the car, was shown to have come from a particular stretch of beach near the city, yet searches of the area provided no evidence. Other forensic work confirmed the association with this beach, yet the connection with the suspects could not be proved. Years later, the kidnappers declared that they had planted the beach sand as a decoy - whether this is true or not remains unclear.
The world's first database of sand grains has been assembled from soils in the United Kingdom, specifically for police forensics. This database contributed key evidence for one of the country's particularly appalling recent criminal cases, the murder of two young Cambridgeshire schoolgirls in 2002. Once again, distinctive soil under the murderer's car tied him to the location where the victims had been
buried.

I know we use sand for glass (and in turn all products that use glass), however, are there any odd or interesting uses for sand that people don't usually know about? Are there any surprising or "out there" uses for sand?

Well, how about computer chips? And all the important minerals (as well as gold, diamonds, sapphires, rubies and garnets) that are found as placer deposits? These include titanium, tungsten, tin, platinum, and niobium. Sand is used as a filter, as a casting method in foundries, in different specialist sports surfaces. Silica and silicon products are used in pharmaceuticals, cosmetics, paper, and paint. Oh, and don't forget concrete.

Is sand a good medium for fossilization to occur in, and if so what signatures would a fossil show in relation to being formed in sandy soil?

Sand is not a great "fossilizer" compared to mud, for example, simply because sand is deposited in very dynamic and high energy environments - beaches, rivers and so on - and is constantly being re-transported by currents and moved on. Organic remains are easily damaged and broken up. That said, a lot of fossils are found in sandstones and trace fossils, footprints, tracks, trails and burrows can be quite common.

Because of the large size of rocks, it can be easy to use distinguishable features to date and classify them by. Can sand grains be dated in the same fashion as a large slab of granite, or do they need a more precise way to measure how old they are?

Dating a rock like granite involves finding the age of cooling and crystallisation of individual minerals through the radioactive isotopes or fission tracks they contain. Some minerals are better for this than others - quartz doesn't contain much in the way of radioactive components, so isn't much help for this. But some minerals that end up as sand grains are - zircon grains are the classics. They are tough as old boots and preserve a very good record of their cooling history. The oldest earthly possessions that we have are zircon sand grains from sandstones in Australia - they're up to 4.2 billion years old. But that's the age of the mineral grains, not the sandstone that now contains them.
One thing we can do with quartz grains is measure how long they have been exposed to cosmic radiation - e.g., how long a sand grain has sat on the surface of a place like the Atacama Desert. There are various different methods all of which are referred to as luminescence dating. It takes an awful lot of work but the results can be amazing - the Atacama has been a desert for far longer than we thought, for example. The USGS has a very good section on the different methods. It's a powerful method for unravelling the history of a landscape and for archaeological research. One example that I particularly like relates to prehistoric rock paintings in Australia. There are no materials that allow dating of the paintings, so their age is often a mystery. However, there are places where now-vanished wasps built their nests over part of a painting, using sand grains in the process. Those sand grains can be dated using luminescence methods and thus give a minimum age for the rock art. I came across exactly the same thing in the Sahara:

I remember sculptures of sand being struck by lightning can occur on beaches at times. My question focuses on how lightning makes sand form into random shapes of "glass" like structures? And when lightning does strike sand, does it have to be a certain type of sand?

It really is glass - the instantaneous and intense heat from the lightning fuses the sand grains into a solid structure, often a tube, and the result is called a fulgurite (from the Latin for lightning). This can happen in essentially any kind of sand and they can be really big - the record is one 17 feet long. They can also be found in ancient sandstones - lightning strikes from a couple of hundred million years ago. Silica glass was also formed by the energy of the first nuclear test explosion at White Sands in 1945 - the sandy soil was fused into glass by the heat. Fulgurites come in all shapes and sizes - the one here is fairly typical:

CB again: Have any additional sand questions for Michael? Leave them in the comments! If you found this blog post interesting, I recommend Michael's book. I have a copy I can loan to NOVA students, or better yet, you can buy your own!

1K

2010-01-29T07:43:00.003-05:00

This is the 1000^th post on NOVA Geoblog.

I passed up the opportunity to engage in anniversarial navel-gazing this past December with the blog's second birthday, opting instead to dish out some recognition to other corners of the geoblogosphere. A thousand posts, being an arbitrary but satisfyingly round number, encourages me to think about what I'm doing with this blog, and where it's going. Today, if you'll indulge me; I offer a few reflections (#1-4) and a request for feedback from you (#2, #5).

1) I've been gratified with all the positive feedback I've gotten (via comments, via e-mail, and in person), mystified at the persistence of some readers in posting argumentative comments, disappointed overall at the lack of commenting, and annoyed at the increasing number of spam comments, which I delete as soon as they come in (a chore). Thanks to everyone who considers this site worth taking the time to read.

2) I'm curious who's reading. I get data that suggests a lot of people are stopping in, but not a lot of people leave comments. If you're a regular, but you don't leave comments, let me extend an invitation to you to say "hi." You can do this via the comments section below, or shoot me an e-mail if you don't want to be all public about it.

3) I enjoy blogging, but I'm also a bit compulsive about it. This blog has existed for 770 days, and the 1000 entries I've posted over that time works out to an average of ~1.3 per day. I'd like to tone that down a bit. In the future, I'm going to give myself permission not to post something every single day. Brace yourselves: I'm going to start applying the brakes.

4) This summer I hope to launch a new geology vodcast series. This has been in the works for some time, and I'm excited that it is finally moving forward. I'm looking for suggestions for a clever title for the series (feel free to leave a comment below if you have a good idea what to call it). It will be available via iTunes and a dedicated YouTube channel. I will also embed the YouTube videos in blog posts here.

5) Lastly, to better determine the future of this blog, I have put together a 5-question survey that I would like to ask you to complete. It is totally anonymous, and will take only 3 minutes of your time. I will leave this survey open for the next 2 weeks, but I ask you to please take the time now to click the link above and complete it. This is for everyone who is reading these words: it's not just for hard-core geologists or for other bloggers. It's for all readers. Thank you!

Patagonia reference post

2010-01-27T07:00:00.003-05:00

Just to get all the Patagonia trip stuff in one easy-to-access reference location:

Birds

The ferry ride from Puero Montt to Puerto Natales

Puerto Natales

Torres del Paine National Park:

Day 1
Day 2
Day 3, part I
Day 3, part II
Day 3, part III
Day 4
Day 5
Day 6, part I
Day 6, part II
Day 7

Argentina: assorted photos

Argentina: Perito Moreno Glacier

Buenos Aires: cemetery & exotic trees

Masoleums and Monkeypuzzles

2010-01-26T07:56:00.002-05:00

This is the final post about my trip to Patagonia. Our final stop was in Buenos Aires, the capital of Argentina. There wasn't much of geological interest that I saw there, but you might like to check out these images of the Recoleta Cemetery, a famous cemetery there. It's full of charming masoleums which are unique in design, and in various states of repair. (Eva Peron is buried here, which is what draws in most visitors.) Here's a view down one of the labyrinthine alleyways:

This masoleum looks like a miniature cathedral:

Several had art noveau details:

This one had an awesome stained glass onion dome bulging out the top:

Two-faced angel statue:

This caught my eye:

The grave belongs to an Argentinian surgeon, Francisco Muniz, who was also into paleontology:

Muniz apparently discovered the first glyptodont (though was not the first to publish it), and corresponded with Charles Darwin. There's a neat little review of his life here, at a website documenting the people interred at Recoleta Cemetery (a great resource if you ever visit it yourself).

Rising from a prominent intersection of pathways in the cemetary was this prominent Araucaria, which I think is a monkeypuzzle tree:

Monkeypuzzles are native to Patagonia, though other members of the genus may be found in New Caledonia, New Guinea, Norfolk Island, and Australia. I love monkeypuzzles: mainly for their awesome name, but also because they look like my idea of what prehistoric plants should look like. Here's one in El Calafate that someone decorated for Christmas:

Closer in, to see some details of its scaly leaves:

Perhaps this is a good image to close out the Patagonia series with, considering it blends the exotic monkeypuzzle with lovely old traditional holiday spirit (at least in my culture). What do I take from this?...

...Amid the prickly hazards of travel, you can find some exceptional gifts.

Perito Moreno Glacier

2010-01-25T07:59:00.005-05:00

Yesterday we looked at some other aspects of Argentina's Parque Nacional Los Glaciares (and the nearby town of El Calafate). Today, some pictures of ice.

Let's orient ourselves first, courtesy of some satellite imagery via Google Maps:

You can see the bright blue of Lago Argentino, including its southern arm, the Brazo Rico. Separating the Brazo Rico from the main part of the lake is the Magallanes Peninsula. And poking out from the white mass at left (the South Patagonian Ice Field) is a nice big valley glacier, the Perito Moreno Glacier. Notice how it pokes right into the Magallanes Peninsula, like a pin approaching a balloon. Occasionally, it surges forward and smooches the opposite shore, cutting the Brazo Rico off from the rest of the lake. When this happens, some spectacular collapses can occur.

The Perito Moreno Glacier is remarkably stable, due in part to its large catchment area and relatively narrow zone of ablation. This means that a bunch of park infrastructure has developed on the Magallanes Peninsula: viewing platforms and docks. The glacier moves forward at the same rate it loses ice through calving/melting: very consistent. We started off with the boat trip up to the glacier's terminus. Here's a view of the boat from above:

...And a view of the glacier's face from the boat:

Ice meets bedrock (plants watch warily):

Looking north from the viewing platform:

A little panorama (two shots spliced together):

So, at this point, I hope I have established that Perito Moreno Glacier is very accessible and very photogenic. It is also a lovely shade of blue. Thank you very much.

A few photos from Argentina

2010-01-24T07:54:00.017-05:00

When you cross the border from Chile into Argentina, you see this sign:

If you aren't familiar with "Las Islas Malvinas," that's because they go by another name in English. Perhaps the detailed map will help clarify the location? The sign refers to the Falkland Islands, currently held by the United Kingdom. So the sign translates to, "The Falklands are Argentinian." The British and the Argentinians faught a war over the Falklands in 1982. The UK won, but Argentina maintains their claims of sovereignty. And as soon as you enter Argentina, they remind you of it. I think they hope you will take pictures of the sign and post them on your geology blog so the world is reminded of what they consider to be an imperial injustice.

The bus ride from Puerto Natales to El Calafate was long -- something like five hours. It went through some very empty country:

As we headed north, with the mountains to our west and wide-open plains to our east, I was reminded of Montana, specifically the Front Range southeast of Glacier National Park. It was very familiar feeling.

The landscape was semi-desert, as the eastward-moving air is drained of its moisture as it crosses the Andes. The rainshadow effect leaves this an area of steppe. The golden grasses draped on the dry hills bring to mind similar landscapes in Mongolia or Africa.

And there are even some birds that you might mistake for African species:

That's our best of many lousy pictures of the Lesser Rhea, also known as "Darwin's Rhea." It's a ratite bird, related to ostriches, emus, cassowaries, kiwi, and elephant birds (the last of which are extinct). The coolest rhea sighting we had was a family of little ones following their mom. The little ones look just like scaled-down miniature adults: Comical!

We stopped at an estancia (ranch) before entering Parque Nacional Los Glaciares, and Lily made friends with a horse there:

She used to have a horse on Hawaii, so this was sweet to see. When we walked off towards the rhea, he followed along, looking for more lovin' from his new American girlfriend.

We were in Argentina to see the massive Perito Moreno Glacier. It is the #1 tourist attraction in Argentina, and is located in Parque Nacional Los Glaciares ("The Glaciers National Park"). Here's our first view of it:

Now here's a test to see how true-blue your geological inclinations run. When you looked at that last picture, did you think to yourself, "What's up with those strata in the lower right? Are those turbidites?"

Yes, indeed. They are:

Alternating sand (blocky) and mud (weathered into low relief) remind us of the Magallanes Basin, which (like most geology) does not stop at the border...

...LA CUENCA MAGALLANES ES ARGENTINA Y CHILENA.

Um, there's two clear joint sets there too.

Around the corner we saw some bivalve fossils and a few clastic dikes ("injectites"). Here's a small clastic dike:

When I brought up clastic dikes the other day when discussing Torres del Paine, Brian responded with some injectite photos of his own. You should check those out. Here's a bigger one from P.N. Los Glaciares:

I've got a ton of photos of Perito Moreno Glacier to show you, but it's really worth saving them for a second post. For now, let's just say: "We went and looked at the glacier for several hours and were very impressed." ...More on that tomorrow.

Then we were bussed back to El Calafate, the town which serves as the main access point for the park, and walked from our hostel towards downtown for some dinner. Along the way, we saw this cool outcrop:

That's very-poorly-lithified silt, peppered here and there with a few cobbles and boulders. The clasts bear scratches, suggesting they are glacially-delivered. The town of El Calafate is on the shore of a big lake called Lago Argentino, and I interpret this outcrop to mean that the lake was much larger and deeper in the past (perhaps dammed by a moraine which has since been partially breached?). In this deeper, earlier version of the lake, icebergs calved off of Perito Moreno Glacier and floated out to melt and drop their sedimentary loads in the offshore sediments. The big boulders and cobbles are therefore dropstones, though I wasn't able to confirm this diagnosis by looking for squished or truncated sedimentary laminations beneath them. (Given that this is earthquake country, I didn't want to be standing underneath those boulders for longer than it took to snap a photo!)

That evening, we had a really world-class meal. Salads and breads and fine Argentinan wine (we skipped the Mendoza stuff and got the Patagonian label, "Saurus." (Yes, as in lizards -- as in "giant, fossilized, terrible lizards"). And for the main course? Well... let's just say that if you're a vegetarian, you should probably stop reading at this point.

The Patagonians herd a lot of sheep, and so they eat of lot of lamb. They have one particular method of cooking this lamb which I was very keen to try because it seems so utterly brutal. Meat is murder, as they say: delicious murder. I am quite aware of the loss of life that comes with the consumption of meat. I have hunted, and I have killed animals in order to eat them. Many people opt not to think about this, and to access their meat in a box or a bag. But to the Patagonians, the death of their animals is both obvious and inoffensive. They slaughter their lamb, gut it and skin it, and then (this is the part that's brutal) they string it up to an iron cross, which is then tilted over a campfire so the lamb can roast slowly. They call it "crucified lamb."

It was delicious -- though the photo may appear shocking to some readers. But, hey: Catholics claim to eat crucified flesh every time they take communion, right? (Apologies in advance to all the transubstantiationists that I just offended.) ...Back to the lamb: I have a special place in my heart for the taste of mutton (I served in Peace Corps Mongolia in 1998-1999), and that familiar gamey tang was present here as well. But it was so much more tender, and served with a garlicky oregano olive oil-based sauce. Oh man, it was good. (Mongolians could learn a lot from Argentinians about how to spice their lamb.) I devoured it, and Lily had to roll me down the street, back to the hostel. Mmmmm....

Okay -- tomorrow you'll get some glacier photos.

Steve Mirsky on Inhofe and Comfort

2010-01-23T08:38:00.005-05:00

In the new issue of Scientific American, vodcast host and prodigious author Steve Mirsky takes on James Inhofe and Ray Comfort. No news here if you're the sort of person who follows climate politics and creationism shenanigans, but his short essay is pretty funny.

Torres del Paine, el ultimo dia

2010-01-23T07:22:00.006-05:00

Well... after a week in Parque Nacional Torres del Paine, it was time to head out of the wilderness and back to the relative civilization of Puerto Natales. We woke on the seventh day, and were pleased to see that the sun was hitting the Cuernos del Paine in a pleasing fashion:

Our tent in the foreground of the Cuernos del Paine:

We made our last batch of camp coffee and our last batch of oatmeal, and then started hiking out. As we walked along, we saw some interesting geology.

Here's a decent little weathering rind. Notice how the initially rectangular profile of this clast is being weathered towards a progressively more bread-loafy shape:

A small dextral fault offsetting turbidite layers:

Looking up into one of the valleys we passed on our way east, we saw an intact glacial end moraine sealing the valley shut.

I'm used to seeing these depositional features bisected by streams, but this one looked just like a wall built perpendicular to the valley trend. Erosion hasn't yet undermined it.

We arrived at the Torres area and fortified ourselves with Snickers bars dipped in peanut butter, then strolled on. There were a great many people there: somewhat shocking to the dirty backpackers...

As we hiked out from the Torres campground/village/tourist extravaganza to the entrance station at Laguna Amarga, we turned around and saw the Torres themselves, namesakes of the park, faintly through the misty distance:

Several kilometers on, we approached the Laguna Amarga Ranger Station, which is situated next to a lovely syncline in the Cerro Toro conglomerate:

Another view, from lower elevation, and closer to the axis of the fold:

Our time in Torres del Paine was unforgettable. Backpacking the Grand Circuit was a travel experience I would recommend to anyone with the ability and temperment to camp and hike in such gorgeous surroundings. It had been the primary goal of our trip, but we weren't done travelling yet. We headed back to Puerto Natales on the bus, and gorged ourselves on pizza that evening. We did laundry, got showered up, and slept like hibernating bears. In the morning, we boarded another bus, one that would take us across the border into Argentina...

TV weathermen skeptical of climate change

2010-01-22T10:33:00.005-05:00

Food for thought: check out this excellent article in the Columbia Review of Journalism ("Hot Air," Jan/Feb issue). Subtitle: "Why don't TV weathermen believe in climate change?"

Hat tip: Anthony Leiserowitz at the Yale Project on Climate Change, who is quoted in the story.

Torres del Paine, day 6, part II

2010-01-22T07:34:00.015-05:00

You'll recall that our sixth day in Torres del Paine National Park had us hiking east from the Paine Grande Lodge. We hiked up over a ridge dividing Lago Pehoe from another turquoise-colored lake, Lago Nordenskjold:

At the so-called Italian Camp, we dropped our packs, and went for a small side hike. We turned to the north, and hiked up the French Valley:

The object of this day-hike was to see some glacier calving. The French Valley is famous for this: you sit back and watch, and big chunks of ice spall off the glaciers, crashing hundreds of feet below onto the rocks. A few seconds later, a sound like thunder reaches you: it was this that we came to experience.

Anybody seen a glacier around here? Rumor is that it was JUST here!

[The line demarcating vegetation above from bare rock below shows former height (and presence) of the glacier.]

Here's a look at the amphitheatre where our glacial show would be performed:

As the clouds cleared a bit, we could see an astonishingly thick cornice of snow/ice atop the mountain peaks. All the valleys up top had been filled in and smoothed off, and there was this white rim atop the black rock. The cornice is probably 40-100 feet thick in this photo:

An annotated photo of the area where we were observing the action:

What happened here was that a much larger glacier (see the vegetation line back a few photos) ablated away, splitting into two upper disconnected feeder glaciers, and a lower glacier which is now semi-buried in rocky debris (talus) and ice spalled off the upper glaciers.

A closer look at the annual growth layers revealed in the lower part of the glacier:

We soon saw some calving events. They were quite cool. Big booming noises, ice explosions seen through binoculars, eating chocolate and almonds. We were happy. Then we heard a roaring noise, like an airplane going overhead. We looked at the glaciers: nothing. What was making that noise? Then, from above, we saw it: coming down out of the clouds was a huge billowing white mass. Apparently, it was coming down from the cornice of snow atop the mountain. An avalanche! An honest-to-goodness avalanche! I have never seen one before; I was giddy at the spectacle. It looks just like a turbidity current, people, but it is white!

It was a magical thing to witness: watching it spread out and poof outward in hundreds of little round turbulent vortices. Everyone in the valley cheered: "YEAHHHH!!!!!"

Tough act to follow... but: Just east of us were the rugged Cuernos del Paine, a series of glacial horns made more photogenic by the pink stripe running through their middles, like a WWF Championship Belt:

This pink stripe is a granitic intrusion, approximately 12 Ma (Miocene*). Here is another photograph of the Cuernos, where the granite is very obvious:

We walked along the north shore of Lago Nordenskold towards the Cuernos campground...

Across the lake, some nice folds were visible:

The Cuernos campground is in this little nook. A lovely place to spend an afternoon and our final night in the park:

And it has very nice views of the Cuernos del Paine:

Seeing the Cuernos was the fulfillment of a decades-old dream for me. I think I saw them in an REI catalog (or perhaps a Patagonia catalog, hmm?) back when I was in college, and thought, "Wow. There's a place on Earth that really looks like that? I gotta go... someday." What I didn't expect then, and was pleased to see now that I was there, was the excellent evidence of stoping, one of the processes by which magma chambers enlarge their size and intrude into other rocks. Stoping is where chunks of the wall rock ("host rock" or "country rock") are broken off by inquisitive fingers of magma, and the liberated blocks (now xenoliths) drop into the magma chamber. Here, you can see (white arrows) some of these splurtles of granite working their way into cracks at the top of the magma chamber:

If these fingers of granite connect up, they separate the block of rock beneath them from the country rock (a form of physical weathering, like root wedging!). More dense than the surrounding magma, the resulting xenoliths sink. If the magma is still rather fluid, the xenoliths may now pile up on the floor of the intrusion. If it's getting to be mushy and semi-crystalline, their downward flow may be retarded, like a slice of banana trying to sink through thick oatmeal. As the granite crystallizes into rock, those xenoliths will be trapped somewhere between the ceiling (source area) and the bottom. Check out the diversity of xenolith positions (white arrows) displayed on this Cuerno:

Great looks at stoping here: some have fallen, some are still beginning to fall. I could easily have spent another two days just hiking along this contact, looking at this intrusive relations.

We spent our final night in the park enjoying the sounds of a nearby waterfall, nature's white noise machine. Only one more day in Torres del Paine...

Meteorite falls in Lorton!

2010-01-22T07:13:00.004-05:00

On Monday, a meteorite crashed into a doctor's office in Lorton, Virginia! Smithsonian scientists confirm its identity as space rock. 220 mph at the moment of impact. Super cool.

NatGeo on Patagonia

2010-01-21T09:06:00.002-05:00

Good timing! National Geographic's new issue (which we got yesterday) discusses many of the same regions of Patagonia that I've been describing here over the past two weeks. You won't find any graded beds in their pages, but they do have some spectactular imagery of the Grey Glacier (via NASA) and the Chilean coast. The NatGeo website has a nice slideshow of photos by Maria Stenzel. The story's lead image is... Torres del Paine.

Torres del Paine, day 6, part I

2010-01-21T07:08:00.004-05:00

You will recall that the first photo I showed you from Patagonia was this one:

That's from just outside the Paine Grande Lodge, where we stayed for our fifth night in the park. I rose at dawn and was fortunate to have the camera handy for a few minutes of good low-angle pink/orange light. By the time the coffee was finished, the sun had risen higher, and the "golden hour" had finished. The mountain now looked like this:

We began the day's hike, headed east along the southern face of the Paine Massif, aiming for the legendary Cuernos ("Horns") del Paine:

A last look back at aquamarine Lago Pehoe, with a Nothofagus tree in the foreground:

I saw a nice example of plumose structure in this boulder (fingertip for scale, far lower left):

After not seeing any conglomerate since the first day of hiking, we started encountering it again, meaning that we had hiked back sufficiently to the east to re-enter the Cerro Toro formation. The conglomerate was varied, and so in one ravine, I took the opportunity to photograph its many guises...

Nice mudstone rip-up clasts in this one:

One final sedimentary shot for this post: another graded bed, as viewed in cross-section:

I love graded beds. They're a key part of the geologic saga at my favorite DC-area locale (the Billy Goat Trail), and the ones in Torres del Paine were just classic: light-colored sand transitioning gradually into darker-colored mud, with a crisp boundary between each graded bed and its neighbors above and below. As noted before, these primary sedimentary structures are formed when a cascading turbidity current slows down and starts dumping its particles. The heaviest drop out first, the lightest in weight drop out last. Each graded bed = 1 turbidity current.

I've got a lot of other shots from Day 6, but I think I'll save them for a second post.

Torres del Paine, day 5

2010-01-20T07:12:00.005-05:00

On Boxing Day morn (Dec. 26), we woke at Refugio Grey, and took our camp stove outside. Just for a lark, we walked over to the shore where an iceberg had beached itself, and popped off a chunk to melt and make coffee:

You haven't really had coffee until you've had coffee made with water that's been locked out of the hydrologic cycle for 14,000 years!

With warm coffee and a granola bar apiece, we walked over the small peninsula where Regugio Grey is located to the bay on the other side. There, a flotilla of icebergs had rafted up against the peninsula. We decided to spend a little bit checking them out, before heading out on the day's (short) hike to the next refugio. We had it all to ourselves:

The icebergs varied tremendously in size, shape, color, and texture.

So, presented with a wealth of icebergs like this, what would you do? If you answered "put one on my head!" then apparently you think the same way that we do:

Silliness expended and coffee consumed, we grabbed our packs and hit the trail again. Today's destination was the Paine Grande Lodge. It wasn't an especially long hike, and it was essentially parallel to Lago Grey for most of the distance. Here's some more icebergs, further down the lake:

One geological site that really caught my attention was this sweet outcrop showing gorgeously folded turbidite layers. To give a sense of scale, each of those green bushes is about 1 meter in diameter:

Here's (white arrow) the Paine Grande Lodge, on the shore of a new lake (you can tell by the color), Lago Pehoe.

Closer in shows the detail of this nice, modern facility:

It was our second night indoors, and while it was a bummer that we had to share our room (6 bunks) with 4 other people, one 'up' side was that the Paine Grande took credit cards, which mean that the pisco sours were on Callan and Lily!

This is the lounge, with a nice woodstove and great views of the landscape for birdwatching or just sitting back and feeling satisfied. We spend a while hanging out here, particularly as a few rain squalls moved through.

The usual routine followed: dinner, bed, dawn, coffee, hiking... on to Day 6!

Torres del Paine, day 4

2010-01-19T07:20:00.004-05:00

Christmas day in Torres del Paine National Park: We packed up our gear at Paso Campground, and hit the trail in the rain. It rained on us for about an hour as we walked south, parallel to the downstream flow of the Grey Glacier, a huge gleaming presence to our right. Occasionally, the trail exited the forest as we had to cross deep ravines, like this one:

Snowmelt coming off the Paine Massif carved these ravines, and the park service had placed ladders in a few key locations, like this one:

Some people didn't like the ladders very much:

Once we got far enough along, we could see the terminus of the Grey Glacier:

Umm, wow.

Slightly different photo composition, with a tree in the foreground:

Nothing but terminus:

Looking south-ish, down the axis of Lago Grey:

Our destination for the evening was Refugio Grey, located on the far side of that first little hook-shaped peninsula.

Iceberg in Lago Grey:

Refugio Grey:

This was our first night spent under a roof on this trip. After three nights in a tent (me with a flat Therm-a-rest), it was quite luxurious to indulge in hot showers and a mattress! We also had a superb Christmas dinner behind those plate-glass windows, eating pork loin and drinking Gato and watching icebergs float by. It was pretty freaking cool.

That afternoon, we went for a walk down the beach, checking out the rocks. There were nice sedimentary structures and nice tectonic structures. Here's some trace fossils seen on one of the bedding planes of the turbidite strata:

I saw a fair amount of bioturbation in the turbidites, but this was without question the best exposure I saw.

Here's a tight little anticline:

Callan takes a nap in a little synclinal bed:

Flame structures with palimpsest glacial striations:

And another set, a few feet over to the right (same bed):

There appear to be some burrows here, too (the little circles of sandstone in the mudstone below the main sandstone contact).

We slept well that night. I was especially pleased by the fact that it rained for half the night (since I was sleeping indoors).

A very brief history of the planet Earth

2010-01-18T15:25:00.002-05:00

Awesome! History of the Earth in 60 Seconds, a video from SEED. Perfect for Historical Geology class!

Via Geology in the West Country.