Did You Know That Pine Mountain Has Moved?
Pine Mountain, in the southeastern corner of Kentucky, sits atop the Pine Mountain Thrust Fault. A thrust fault is a tear in the upper part of the Earth's crust along which one block of strata is pushed up and over another block of strata. This is a different kind of movement than the normal faults of the New Madrid Fault Zone (in the Jackson Purchase of western Kentucky), in which movement along the fault is vertical and one block drops down relative to the other, or strike-slip faults like the San Andreas Fault Zone in California, in which movement is in a lateral direction, with one block sliding past the other.
The illustration above is a view of the rocks beneath Pine Mountain from the Frakes Geological Quadrangle Map (Newell, 1975) in southeastern Kentucky. Each of the colors on the illustration represent a different unit of rock. You can see that the rocks on the right of the diagram (southeast direction) are tilted and pushed over the rocks on the left side of the diagram (northwest direction). This movement can be seen all along the leading edge of Pine Mountain, which is more than 90 miles (135 km) long. The fault block, which includes Pine Mountain, actually continues to the southeast into Virginia and Tennessee and is thousands of feet thick. You can imagine the forces required to push this large a block of material! The force was provided by the collision of the North American continent with Africa and Europe at the end of the Paleozoic Era, more than 275 million years ago. The collision formed the Appalachian Mountains and a series of thrust blocks, each one pushed to the northwest over the next. Pine Mountain is the westernmost thrust block.
Geologists can trace the amount of movement on the fault. The northern portion of Pine Mountain, north of the town of Louellan, has been thrust 4 miles (6.4 km) from its original position. The southern edge in Tennessee has been moved 11 miles (17.6 km)! The area that is now the city of Harlan has been moved 6 to 8 miles from where it started. If you live in Harlan, don't worry, movement along the fault stopped millions of years ago.
References that include information about Pine Mountain. If your library does not have these references, they are available from the Publications Sale Office of the Kentucky Geological Survey.
- McGrain, Preston, 1983, The geologic story of Kentucky: Kentucky Geological Survey, Series 11, Special publication 8, p. 43-45
- Geologic Quadrangle Maps in Kentucky show the leading edge of the thrust fault in cross section and can be used to illustrate movement on the fault. If your library does not have these references, they are available from the <link to>Publication Sales Office of the Kentucky Geological Survey.
- Englund, K. G., 1964, Geology of the Middlesboro South Quadrangle, Tennessee, Kentucky, Virginia: U.S. Geological Survey Geological Quadrangle Map, GQ-301.
- Froelich, A.J., 1972, Geologic map of the Wallins Creek Quadrangle, Harlan and Bell Counties, Kentucky: U.S. Geological Survey Geological Quadrangle Map, GQ-1016.
- Froelich, A.J., and Tazelaar, J.F., 1973, Geologic map of the Balkan Quadrangle, Bell and Harlan Counties, Kentucky: U.S. Geological Survey Geological Quadrangle Map, GQ-1127.
- Newell, W.L., 1975, Geologic map of the Frakes Quadrangle and part of the Eagan Quadrangle, southeastern Kentucky: U.S. Geological Survey Geological Quadrangle Map, GQ-1249.
- Rice, C.L., and Maughan, E.K., 1978, Geologic map of the Kayjay and part of the Fork Ridge Quadrangle, Bell and Knott Counties, Kentucky: U.S. Geological Survey Geological Quadrangle Map, GQ-1505.
- Rice, C.L., and Newell, W.L., 1975, Geologic map of the Saxton and part of the Jellico East Quadrangle, Whitley County, Kentucky: U.S. Geological Survey Geological Quadrangle Map, GQ-1264.