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Mesquite Flats Dune Field

A cache by TerryDad2 Send Message to Owner Message this owner
Hidden : 5/2/2011
Difficulty:
2 out of 5
Terrain:
3 out of 5

Size: Size: not chosen (not chosen)

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Geocache Description:

The Mesquite Flats Dune Field provides an example of traverse dunes showing a clear dominant wind direction. Both ripples and dunes can be observed here.

The Mesquite Flats Dune Field is easily accessible. There is a paved parking area with spaces for large RVs and trailers and a set of restrooms. The dunes start a short walk from the parking area. Once on the dunes there are no specific trails.

As with all locations in National Parks, everything is protected, so leave it as you found it.

This dune field is thought to be about 2,000 years old. It sits on five to seven kilometers of alluvial fill, the thickest alluvial fill in Death Valley. Dunes are classified by the different shapes they make (http://www3.interscience.wiley.com:8100/legacy/college/strahler/0471238007/animations/ch19_animations/animation4.html). Each of these dune types is characteristic of the predominant direction of the wind. The dunes in the Mesquite Flats Dune Field are predominantly transverse dunes. These types of dunes form where the wind typically comes from the same direction all the time.

Eolean Transport
The sand of these dunes has been transported to this location by the regional winds. Like water, wind transports grains by one of three methods, suspension (picked up by the wind and carried along with it), saltation (grains that are picked up, moved a short distance then fall back down, bouncing), or impact creep (grains that are nudged along by saltating grains) depending upon the speed of the wind and the size of the grain. Only the smallest and thus lightest grains can be suspended by air, while the heavier grains either saltate or are moved by impact creep.

These processes can be seen in a video by Kansas State University (http://www.weru.ksu.edu/new_weru/multimedia/movies/dust003.mpg)

The moving sand quickly begins forming ridges. These ripples are a few inches from ridge to ridge and less than an inch high. These ridges form as grains saltate from one crest to the other. Finer grains are eroded away from the ridges and are left in the relatively protected troughs between the crests. This results in a patter of larger grains on top of finer grains. This characteristic distinguishes aeolian deposition from ripples deposited by water. Over time the ripples migrate in the direction of the wind.

The large dune forms as sand begins to accumulate in larger ridges. The ripples and other particles move up the windward side of the dune. When the sand builds up the top of the dune too steeply, the ridge collapses. The angle that the sand begins to slide is called the angle of repose. Over time this process slowly migrates the dune in the direction of the wind.

The Source of the Sand
All this sand had to come from somewhere. It is likely that the sand comes from the many alluvial fans of Death Valley. Death Valley Wash is also in the path of the predominant wind flow and likely contributes sand to the dune field.

Sand Composition
From a distance only the tall active dunes are easily identifiable and appear made of one type of sand. Closer inspection reveals a variety of minerals can be found in the dunes. The light colored quartz and feldspar predominate. However, the wind patterns concentrate darker heavier minerals near the surface of the dune and ripple crests. These darker minerals are magnetite and amphibole. You can use a magnet to easily pick up the small bits of magnetite.

Logging requirements:
Send me a note with:

  1. The text "GC2VGA8 Mesquite Flats Dune Field" on the first line
  2. The number (including non-cachers) and names of the geocachers in your group.
  3. Based on the shape of the dunes, what direction does the wind usually come from?
  4. What feature is downwind of the dune field that would slow the wind to deposit sand here (think big)
  5. If you have a magnet, find some magnetite.

The following sources were used to generate this cache:

  • Spear, Steven G. Ph.D., 2009, Death Velley Geology, A Field Guide and Virtual Tour of the Geology of Death Valley National Park and Environs, California and Nevada, Last Updated: August 25, 2009 http://www.palomar.edu/geology/DVWeb.htm
  • USGS, Eolian Processes, http://pubs.usgs.gov/gip/deserts/eolian/, Last modified 10/29/97
  • Robert S. Anderson & Kirby L. Bunas Grain size segregation and stratigraphy in aeolian ripples modeled with a cellular automaton, Nature 365, 740 - 743 (21 October 1993); doi:10.1038/365740a0 http://www.nature.com/nature/journal/v365/n6448/abs/365740a0.html
  • Saltation (geology), Wikipedia, http://en.wikipedia.org/wiki/Saltation_(geology), last modified on 9 April 2010 at 16:52
  • Indiana University, Week 8 Deserts and Glaciers http://www.indiana.edu/~g103/G103/Week8/week8.html

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