Evangeline Terrace EarthCache
Hidden : 2/15/2012
Difficulty:
1.5 out of 5
Terrain:
1.5 out of 5

Size: Size: other (other)

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Geocache Description:


The coordinates for this earthcache bring you to a rare sight in south-central Louisiana: a sudden elevation change. How this could be, is an amazing geological journey over many millions of years.

At the end of the Cretaceous Period (about 95 million years ago) all of this part of the North American continent was underwater. Millions of years of sandy ocean bottom now make up the bedrock under this part of Louisiana.



North America has since risen upward and the inland seas are no more. But over the last 2 million years, vast continental glaciers have advanced and retreated at least five times. These glaciers did not advance as far south as Louisiana, but the rivers of meltoff they produced became the rivers that found their way to the Gulf of Mexico, and the sands and gravel the glaciers ground down from mountains became the land which is now the Gulf Coast Plain and Continental Shelf.



The glaciers' chilling effect on the winds of North America were so extreme that the downdrafts and cyclones they created literally blew dunes of earth away. This silt is known as loess and it also was carried away by the rivers and also were deposited all across the American Southeast. These sands also produced the deposits which make up a great aquifer system that holds fresh water in vast volumes underneath the Gulf Coast Plain.

The Mississippi River system slowly made its alluvial valley through the heart of North America, depositing great fans of silt as it went. This river system has changed course many, many times, as runoff from the glaciers increased or decreased. The Holocene Epoch began at the end of the last glacial retreat, about 12,000 years ago. By three thousand years ago, the sea reached its present level, and the Mississippi river has chosen a more direct route to the Gulf.






INSTRUCTIONS FOR LOGGING THE EARTHCACHE:

1. Measure or estimate the difference in elevation between the land at the earthcache location and the lower land level.

2. Using information from the description above... What do you think has caused this steep elevation change here? What natural process(es) has/have done this?

3. Describe what you think this location has looked like at different stages of the Holocene epoch.

4. Explain how you think it is that the soil on the terrace above is generally more reddish and sandy but the soil on the level below is dark?

5. Email your answers to the CO and log found. Photos are encouraged.


Sources:

Kniffen, F.B. and Hilliard, S.B., 1988, Louisiana, its land and people: Baton Rouge, La., Louisiana State University Press, 213 p.

B. Pierre Sargent, 2004, THICKNESS OF THE CHICOT AQUIFER SYSTEM SURFICIAL CONFINING UNIT AND LOCATION OF SHALLOW SANDS, SOUTHWESTERN LOUISIANA: U.S. GEOLOGICAL SURVEY
Published by LOUISIANA DEPARTMENT OF TRANSPORTATION AND DEVELOPMENT

Ice Age (Pleistocene Epoch), http://www.epa.gov/gmpo/edresources/pleistocene.html

Image Credits:

E. Arthur Bettis III, Daniel R. Muhs, 2002, Last Glacial loess in the coterminous USA: Quaternary Science Reviews 22 (2003)

David C. Weindorf, 2008, An Update of the Field Guide to Louisiana Soil Classification - LSU AgCenter Research Bulletin #889

Sonja Spasojevic, Lijun Liu, and Michael Gurnis, 2009, North America regional sea level since the Late Cretaceous from adjoint convection models: Seismological Laboratory, California Institute of Technology, Pasadena, CA

Additional Hints (No hints available.)



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