Sand Dune Week: The Sand Hills

Long time no post!

I hear it is sand dune week, so I thought I would make a little post.

The Sand Hills of western Nebraska are North America's largest sand dune formation, covering some 50-60,000 square km. Formed during the late Pleistocene and Holocene from eolian deposits, they consist of a mixture of sand sheets, transverse, liner, and parabolic dunes. The dunes are vegetatively stabilized, but during long term droughts, reduced vegetation cover allows dune movement, primarily to the southeast. Interdune areas often intersect with the water table, resulting in lakes and wetlands. Because the sandy soil limited plowing, they mostly remained grass covered. The Sand Hills are the most ecologically intact section of the Great Plains.

Such a large feature is necessarily best viewed from above.

Compound Parabolic Dunes between Alliance and Hyannis

Closer to the ground, patterns are much more difficult to discern.

Transverse Dunes at Valentine NWR

References
Loope, D. B. Swinehart, J. B. Thinking Like a Dune Field: Geologic History in the Nebraska Sand Hills. Great Plains Research 10:5-36. 2000.

The Sandhills

Earth Observatory Image of the Day

Map Monday 19: Bathymetry of Lake Baikal

Lake Baikal is most famous for being the deepest and most voluminous lake in the world [assuming you don't count the Caspian Sea]. For me, the most striking feature isn't the deepest point, but rather, the average depth at 744 meter. The bathymetry, instead sloping to the lowest point, it has steep sides and a flat bottom. Image a fjord, although it isn't glacial in origin, rather tectonic. This oblique DEM gives another perspective.

Map Information
The INTAS Project 99-1669 Team. 2002. A new bathymetric map of Lake Baikal. Open-File Report on CD-Rom

Riviére de Terre

Riviére de Terre by Andy Goldsworthy; photo by Emmanuel Prunevieille.

This month's Accretionary Wedge is geo-images. Although, I do like maps, I went with something different.

I first learned of the land artist Andy Goldsworthy through the documentary Rivers and Tides. As the name "land artist" implies, various "natural" materials, such as rocks, twigs, leaves, soil are used in the creation and placement of the art. Many of the features are temporary, being "destroyed" by the nature around it.

The work is made of a variety of local clays, forming the work as the clays dried.

Map Monday 18: 1911 Mount St Helens

With the 30th anniversary of the 1980 eruption coming up tomorrow, why not a pre-eruption map? The below is the 1919 Mt St Helens quadrangle. Be sure to click on the image for a zoomable version of the map.



Map Information
U.S. Geological Survey. 1919. Mount St Helens quadrangle, Washington 1:125,000. United States Department of the Interior, USGS. Hosted by University of Washington.