GC205HK Southeastern Louisiana Fault Scarp (Earthcache) in Louisiana, United States created by bob.bobson

This cache has been archived.

bob.bobson: Thanks to all of you who visited. I am archiving this Earthcache because the picture links are broken, the reference link is broken (both of which degrade its educational value), and I haven't been to the site in a while, so I don't know what the conditions on the ground are.

GC205HK ▼

A cache by bob.bobson Message this owner

Hidden : 10/22/2009

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Size: Size: not chosen (not chosen)

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Geocache Description:

The seemingly insignificant slope 250 feet to the south of your current position is a signature of massive tectonic forces at work miles below the Earth’s surface. The changes caused by these tectonic forces are very slow but of very long duration. Therefore, the cumulative effect of these changes has a significant influence on the culture, economy and ecology of southeast Louisiana.

The small slope is in fact an escarpment of the Tepatate-Baton Rouge fault system. The ground that you are standing on is stable with respect to the rest of North America, while the ground on the other side of the fault is moving southward at 2 millimeters/year (0.1 inches/year) and downward at 5 millimeters/year (0.2 inches/year). This motion is essentially a large, slow-moving landslide, as a large slab of southeastern Louisiana, referred to as the South Louisiana Allochthon appears to have broken away from the location in which it was formed. [See reference.] The moving slab is approximately 150 miles wide by 200 miles long by 5 miles thick as shown in Figure 1 and Figure 2.

Figure 1. Plan view of Tepatate-Baton Rouge fault and approximate extent of South Louisiana Allochthon. Adapted from reference.

Figure 2. Cross-section of Tepatate-Baton Rouge fault and South Louisiana Allochthon along line A-A’ in Figure 1. Adapted from reference.

This type of breakaway is not unusual in the geologic history of the Mississippi River Delta and the Gulf of Mexico Basin. The Mississippi River deposits massive amounts of sediment onto the North American continental shelf, which builds up until it reaches a point of being unstable, at which time it breaks away and slides into a more stable position. The downward motion of the allochthon contributes to coastal loss and lowering of flood-control structures in southeast Louisiana. Understanding and forecasting geological processes such as this are critical for designing appropriate long-term flood protection and coastal restoration strategies for South Louisiana.

Glossary:
tec-ton-ic [tek-TON-ik]: referring to the forces or conditions within the Earth that cause movements of the crust

es-carp-ment [i-SKAHRP-muhnt] a long, precipitous, clifflike ridge of land, rock, or the like, commonly formed by faulting or fracturing of the earth's crust

al-loch-thon [uh-LOK-thuhn]: a geological formation not formed in the region where found and moved to its present location by tectonic forces

To log this cache, you must do the following:

1. Take a picture of yourself with the fault in the background. Post it with your log.

2. Answer two questions. E-mail your answers to me.
a. What is the (approximate) height of the fault scarp (i.e. the difference in elevation between the land to the north of the scarp and the land to the south of the scarp)?
b. Using the equation: height = (5 millimeters/year) x (time) or height = (0.2 inches/year) x (time), what was the approximate time required for the fault scarp to reach its current height?

Reference: Tectonic control of subsidence and southward displacement of southeast Louisiana with respect to stable North America; Roy K. Dokka, Giovanni F. Sella, and Timothy H. Dixon; Geophysical Research Letters, vol. 33, L23308; 2006.

Acknowledgment: Inspiration for this Earthcache was provided by S.N.

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Southeastern Louisiana Fault Scarp EarthCache

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