Falls Creek Coal Seams, Kachemak Bay

Falls Creek Coal Seams, Kachemak Bay

by | Jul 8, 2019

Falls Creek is a stream on the Kenai Peninsula that flows south for 4.5 miles (7.3 km) to Kachemak Bay, about 17 miles (27 km) northeast of Homer, Alaska. The local name was first reported by R.W. Stone of the U.S. Geological Survey, and probably so named because of the drop in elevation along the course of the stream.

The eroding bluffs at the head of Kachemak Bay are comprised of fine-grained sedimentary rocks of the Kenai Group, a sequence formed during the middle to late Cenozoic (about 50 million years ago). This rock formation comprises the only bedrock along the coast between Kenai and the Fox River. The geologic unit is exposed almost continuously in the precipitous wave-cut cliffs and steep walls of stream canyons. The sequence consists of at least 5,000 feet (1,500 m) of moderately to weakly hardened, locally conglomeratic sandstone with interbedded siltstone, claystone, and coal seams. The proportion of sandstone increases northward and the number and thickness of coal beds and the quality of the coal decreases. The coal is relatively low grade lignitic to sub-bituminous. Coal beds are generally lenticular, ranging from 3-7 feet (1-2 m) thick. Many former coal beds have been burned, thus baking the adjacent rocks a distinctive brick-orange color.

The rock is highly friable and actively mass wasting to form deep gullies. Talus cones develop at the base of the sea cliff from accumulating rock fragments. These deposits typically have a concave upward shape, and the maximum inclination of these deposits corresponds to the angle of repose for the mean particle size. Read more here and here. Explore more of Falls Creek here:

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