Earthquake at Lacon Mountain – I-65 Earthcache
This is a roadside Earthcache.
Finding Ground Zero:
If you are traveling on I-65, take Exit 318 and then go south on Hwy 31. Stop at the green sign - Birmingham, Nashville, on the north side of Hwy 31(April 2018 - Apparently the GREEN SIGN has been knocked down - until it is replaced, just stop at GZ and look in the direction of 292 degrees). There is plenty of room to safely park here off the roadway. I HIGHLY RECOMMEND THAT YOU USE A PAIR OF BINOCULARS TO AIDE IN LOOKING FOR THE FAULTLINE. Morning light is best time to view this old Fault Line, but afternoon sunlight will also work, just not as well. This Earchcache CAN NOT be done at NIGHT. Use the compass on your GPS or Smart Phone and while standing near sign, look at the limestone rock wall located at a Bearing of 292 degrees. Look at the lowest horizontal layers of limestone in the rock wall. At the bearing of 292 degrees, you will notice that there is misalignment of the layers of rock on each side of this bearing. The line formed by the break in the rock layers is the site of an ancient earthquake. This line is called a FAULT. Directly at the site of the fault the rocks seem to be jumbled or confused. The Fault Line that formed when this earthquake occurred runs through Lacon Mountain at a heading of 330 degrees. Following the Fault Line up to the highest visible layers of rock at a bearing of 294 degrees, you can see the continuation of the Fault Line. The rock here along the Fault Line are also jumbled and confused in appearance. You can see this Fault Line up close by going to the second waypoint listed here and looking behind the large ground level Cedar Tree. Going to this second Waypoint is not required to complete this Earthcache.
Earthcache:
This is an Earthcache and as such is a kind of virtual cache in that there is no physical container to find and log to sign. You must answer the questions below and then email or message the correct answers to Papa Bear 204. Any “Found Log” that is not accompanied with an email with the answers will regrettably be deleted.
Read the Educational Reading below before attempting to answer the Questions below.
Questions:
1. Are the rock layers on the Northside of the Fault higher or are the rock layers on Southside higher?
2. Estimate the difference in height of the layers on each side of the fault. (Imagine a five foot tall person standing next to the Faultline and use that as a scale to make your estimate)
3. Are there any other Faultlines visible along the entire length of the limestone rock wall here?
4. Why do you think the rocks right along the Fault Plane are jumbled or confused?
5. Do you think this is a Normal Fault or a Reverse Fault?
Educational Component:
Faulting – fracturing of rocks in the Earth due to breakage and movement of material along the fracture or Fault Plane. Caused by compressional, tensional, and shearing forces.
Fault plane – the surface along which a rock formation fractures and slips.
Forces That Cause Rocks To Deform, Fracture, and Move:
1. Compression – is the application of force from opposing directions. These opposing forces can cause solid rocks to become squeezed, squashed, or compacted. The opposing forces can cause rocks to fracture, break, become deformed, and move upward along the fracture line.
2. Tensional - refers to a stress which stretches rocks in two opposite directions. The rocks become longer in a lateral direction and thinner in a vertical direction. Tensional stress can cause rocks to fracture and move apart or slid along the fracture line in opposite directions.
3. Shearing – forces that push two sides of an object in opposite directions. Shearing large blocks or plates of rock to move along each other in opposite lateral directions.
Types of Faults:
1. Dip-Slip Fault – relative movement up or down the fault plane.
2. Normal fault – dip slip fault where the rocks below the fault plane move upwards – caused by extensional forces or tensional forces
3. Reverse fault – dip slip fault where the rocks below the fault plane move downwards – caused by compressional forces.
4. Strike-slip fault – fault whose movement is horizontal, parallel to the strike of the fault plane – caused by shearing. Right lateral fault – strike slip with movement to the right, Left lateral fault, strike slip fault with movement to the left.
5. Oblique-slip fault – fault where move is simultaneously along strike and either up or down – movement at an angle along the fault plane.
6. Thrust fault – very low angle reverse fault where one formation is thrust over another – process called over-thrusting.
Age of the Lacon Mountain Limestone:
The limestone rocks seen here that make up Lacon Mountain are thought to be Mississippian Period in age. That means that these rocks are probably between 359.2 and 318 Million years old. The fault line seen here cuts through the all of the Limestone Layers, so the Faultline and resulting earthquake event are younger than 318 Million Years ago.
Cited Sources:
https://www.uwgb.edu/dutchs/StateGeolMaps/Al-MsGMap.HTM
https://en.wikipedia.org/wiki/Compression_(geology)
https://en.wikipedia.org/wiki/Tension_(geology)
http://homepage.usask.ca/~mjr347/prog/geoe118/geoe118.051.html