Labels: dc, museums, oceans, smithsonian
The largest meteorite (or maybe comet?... we don't really know which) impact crater in the United States is in Virginia, underneath the lower Chesapeake Bay. In the Eocene, a large bolide (unidentified space chunk) slammed into the Earth. Dating of microfossils found in the same sedimentary layers as impact ejecta have provided a date of ~35.5 Ma for the event. The impactor hit on the continental shelf offshore of Eocene Virginia, carving through the Atlantic-deposited sediments there and gouging into the crystalline bedrock beneath (igneous and metamorphic rocks like the modern Piedmont province, but buried beneath Coastal Plain layers).
The crater was discovered over a ten-year process that began with offshore sampling near Atlantic City, New Jersey in the mid-1980s. Those drill cores came up with a layer of ejecta (including shocked quartz and little beads of glass called tektites) among the late Eocene layers of sediments. Searching around, eventually the crater was seismically imaged by oil exploration in the Chesapeake Bay in the mid-1990s.
Centered on Cape Charles, Virginia, the crater is about 50 miles across, but appears wider as sedimentary layers adjacent to the hold have slumped inward along listric faults. The James, York, and Rappahannock Rivers all trend into this depression, and ultimately the crater is probably responsible for the Susquehanna River taking on its southerly course. When sea level rose and flooded the valley of the Susquehanna, the Chesapeake Bay was formed.
A similar impact structure offshore of New Jersey, the Toms Canyon Impact Crater, may have formed at the same time as the impactor broke into pieces before impacting.
The lead-off image to this post is by the team at the U-Haul trucking company, which performs a terrific public service by finding out interesting things about the different states (and Canadian provinces) and posting them on the sides of their trucks with eye-catching graphics. A great many of the topics they choose are about geology, from minerals to fossils to impact craters to cartography and canyons. A while ago, I wrote an article for Geotimes looking at their program.
More information on the crater:
Wikipedia's entry on the crater.
W&M Geology Department's page about the crater.
USGS team examining the crater.
National Geographic article (2001).
Labels: art, cenozoic, coastal plain, geology, meteors, new jersey, piedmont, rivers, virginia
Labels: canada, dc, geologic time, news
As for why geobloggers bother with blogging, the most common response was that they wanted to share information and perspectives with others, followed closely by the sense of connecting with other interested individuals and public outreach. A significant minority also mentioned the pleasure they take in the act of writing, or a desire to practice/improve their writing skills. Some comments from the survey on why geobloggers blog:
Labels: climate change, news, politics
Program Summary
How Fast is Atmospheric CO2 Growing and Why, and Does it Suggest Ways to Mitigate Climate Change?
The increase in atmospheric carbon dioxide (CO2) is the single largest human perturbation of the climate system. Its rate of change reflects the balance between human-driven carbon emissions and the dynamics of a number of terrestrial and ocean processes that remove or emit CO2. It is the long term evolution of this balance that will determine to a large extent the speed and magnitude of climate change and the mitigation requirements to stabilize atmospheric CO2 concentrations at any given level. Dr. Canadell will present the most recent trends in global carbon sources and sinks, updated for the first time to the year 2007, with particularly focus on major shifts occurring since 2000. Dr. Canadell’s research indicates that the underlying drivers of changes in atmospheric CO2 growth include: i) increased human-induced carbon emissions, ii) stagnation of the carbon intensity of the global economy, and iii) decreased efficiency of natural carbon sinks.
New Estimates of Carbon Storage in Arctic Soils and Implications in a Changing Environment
The Arctic represents approximately 13% of the total land area of the Earth, and arctic tundra occupies roughly 5 million square kilometers. Arctic tundra soils represent a major storage pool for dead organic carbon, largely due to cold temperatures and saturated soils in many locations that prevent its decomposition. Prior estimates of carbon stored in tundra soils range from 20-29 kg of soil organic carbon (SOC) per square meter. These estimates however, were based on data collected from only the top 20-40 cm of soil, and were sometimes extrapolated to 100 cm. It is our understanding that large quantities of SOC are stored at greater depths, through the annual freezing and thawing motion of the soils (cryoturbation), and potentially frozen in the permafrost.
Recent detailed analysis of Arctic soils by Dr. Epstein and his colleagues found that soil organic carbon values averaged 34.8 kg per square meter, representing an increase of approximately 40% over the prior estimates. Additionally, 38% of the total soil organic carbon was found in the permafrost.
A total of 98.2 gigatonnes (1015 grams) of carbon is estimated to be stored in the soils of the North American Arctic tundra. An area-based estimate for the entire Arctic suggests the presence of approximately 160 gigatonnes of carbon. The annual increase in atmospheric carbon dioxide is roughly 2% of this amount, so small changes in Arctic carbon storage could have substantive impacts on atmospheric CO2. The future of this stored carbon is, however, largely uncertain in the face of a changing Arctic environment. Climate change and resulting increasing temperatures in much of the Arctic could increase the decomposition rates of soil organic carbon (producing atmospheric CO2), and increase permafrost thaw, which would expose more soil organic carbon for decomposition. On the other hand, increasing temperatures could also lead to greater sequestration of atmospheric CO2 by tundra vegetation. Actual changes will be the result of complex interactions between processes that sequester carbon and those that release it.
Past, Present and Future Changes in Permafrost and Implications for a Changing Carbon Budget
Presence of permafrost is one of the major factors that turn northern ecosystems into an efficient natural carbon sink. Moreover, a significant amount of carbon is sequestered in the upper several meters to several tens of meters of permafrost. Because of that, the appearance and disappearance of permafrost within the northern landscapes have a direct impact on the efficiency of northern ecosystems to sequester carbon in soil, both near the ground surface and in deeper soil layers. Recent changes in permafrost may potentially transform the northern ecosystems from an effective carbon sink to a significant source of carbon for the Earth’s atmosphere. Additional emissions of carbon from thawing permafrost may be in the form of CO2 or methane depending upon specific local conditions.
Dr. Romanovsky will present information on changes in terrestrial and subsea permafrost in the past during the last glacial-interglacial cycle and on the most recent trends in permafrost in the Northern Hemisphere. He will further discuss the potential impact of these changes in permafrost (including a short discussion on potential changes in methane gas clathrates) on the global carbon cycle. Dr. Romanovsky’s research suggests that permafrost in North America and Northern Eurasia shows a substantial warming during the last 20 to 30 years. The magnitude of warming varied with location, but was typically from 0.5 to 2°C at 15 meters depth. Thawing of the Little Ice Age permafrost is on-going at many locations. There are some indications that the late-Holocene permafrost started to thaw at some specific undisturbed locations in the European Northeast, in the Northwest and East Siberia, and in Alaska. Future projections of possible changes in permafrost during the current century, based on the application of calibrated permafrost models, will be also presented.
The next seminar is tentatively scheduled for October 10, 2008.
Topic: Ecosystem Health in a Rapidly Changing Climate
Please see the AMS web site for seminar summaries, presentations and future
events: http://www.ametsoc.org/seminar
For more information please contact:
Anthony D. Socci, Ph.D. Tel. (202) 737-9006, ext. 412 socci@ametsoc.org
UMD: 11:00am - 12:00pm at 1121 Computer Science Instructional Center
Internal flow and extrusion of the Greater Himalayan Slab, Mount Everest Massif: a tour of the world's highest rocks
Dr. Rick Law from Virginia Polytechnic Institute and State University
If you are interested in meeting with Dr. Law please sign up online. You also may delete an appointment from this page. Please join the faculty and students for refreshments in the Geology Building foyer at 10:30 am.
Seminar series web page for UMD-College Park Geology.
Labels: climate change, CO2, geology, global warming, maryland, meetings
I saw David Byrne (formerly the frontman of the Talking Heads) perform last night in Baltimore. He did a great job, as he always does. (This was my fourth time seeing him in concert.)"Letting the days go by/let the water hold me downOn oceanography:
Letting the days go by/water flowing underground
Into the blue again/in the silent water
Under the rocks and stones/there is water underground"
"Water dissolving...and water removing
There is water at the bottom of the ocean
Carry the water at the bottom of the ocean
Remove the water at the bottom of the ocean!"
On the principle of uniformity ("uniformitarianism"):
"Same as it ever was, same as it ever was,
Same as it ever was, same as it ever was"
Also, from a different Talking Heads tune ("Life During Wartime"), Mr. Byrne offers us this epistle, clearly referring to the value of studying for open-book geology lab practicals:
"Burn all the notebooks
What good are notebooks?
They won't help me survive!"
Mr. Byrne may be coming to a concert hall near you. Check out his tour dates here. Listen to his new album for free online here. He also keeps a blog (which he calls a "journal," and it occasionally features geological musings, as in this example.)
Labels: geology, music, oceans, water resources
Labels: hurricanes, news, texas
Labels: fossils, mammals, meetings, oceans, psw, smithsonian
Labels: appalachians, climate change, global warming, new york, rain, sediment, snow
I had a great time on this trip: felt like we all really bonded and had a fun adventure. Thanks to all the students who went and to the Student Activities counselor who co-led the trip with me, Jessie Zahorian! It was fun!
Labels: caves, field trips, nova, travel
Labels: geologists, virginia
Labels: climate change, global warming, oil, prius, tech
Labels: alaska, canada, climate change, global warming, russia
