Introduction
The Palouse Falls is found southeast of Washington, US, on the Palouse River as it enters Snake River. Although a series of falls were formed along the river, the Palouse Falls is today the only one surviving, dropping water through a distance of an estimated 200 feet.
The waterfall is a breathtaking site visited by thousands of people annually. The Palouse Falls is thought to have been formed as a result of the heavy flooding which occurred upstream when the glacial Lake Missoula burst, releasing massive volumes of ice and glacier.
The flood material cut long and deep channels, called coulees, that formed 3 waterfalls at the confluence of the Snake River and the Palouse River. With each flooding, the waterfalls moved upstream until the present day structures were formed.
Palouse Falls contains many different types of rocks that were formed from glacial floods during the ice age era just before the Palouse River entered the Snake River. The rocks, of which basalt is the most common, are mostly metamorphic and were formed as a result of the cooling of floodwaters and ice.
These rocks were formed from the floodwaters from Lake Missoula that flowed across eastern Washington during the Pleistocene era (Alt 23). The basalt rocks are estimated to be around 15,000 years old.
Structures and interesting landforms visible on the geologic map
Palouse River was formed as a result of glacial floods that originated from the glacial Lake Missoula, however, little evidence is left of this massive activity of which the most visible is the Palouse Falls. Today, the water has eroded the walls of the rocks, exposing layers of basalt rocks.
The basalt is formed of layers from flows at various periods, some of which are nearly 100 feet thick. Another structure is the plunge pool. The plunge pool is formed as the dropping water erodes the rock below and the side of the canyon where it originates, this continuous abrasion and erosion causes the base of the waterfall to move backwards as seen in the Palouse Falls base (Alt 12).
This eventually causes the rocks in the upper parts of the waterfall to fall off, consequently making the whole waterfall to move upstream. Various structures can be seen on the rocks surrounding the Palouse Falls that explain its geology, including plunge pools, kolk created potholes, hanging coulees and rock benches. These structures draw thousands of visitors to the park area.
Surrounding the Palouse River are the Palouse Hills that were made out of fine particles deposited by winds during the last phase of the Pleistocene era. Outcrops of basalt rocks are also visible in the surrounding area. These rocks are volcanic and reflect the huge eruptions that occurred in the area during the Miocene period.
These eruptions occurred in present-day central Washington and resulted in the release of large volumes of lava to the surface. From the different layers of these rocks, geologists have concluded that the eruptions and subsequent laval flows occurred more than once (Bacon 61).
The basalt rocks have turned orange (clay colored) due to weathering processes that occur when the rocks are exposed to weathering agents such as water and air.
The size of the ‘bowl’ into which the Palouse Falls drops its water is many times larger than the river itself and this suggests that a force larger than the river carved it out. Geologist studies have determined that this bowl was created by huge outburst flooding of the glacial Lake Missoula as massive ice volumes from the lake moved along (Carson para. 2).
The series of floods were at first triggered when glaciers from the north advanced, or the ice broke due to its weight, letting the glacial lake to burst out, pushing everything on its way downstream. The moving ice and debris cut across the land creating long and deep coulees. These structures dot the area around the Palouse Falls.
Geologic History of the Palouse Falls
The area around eastern Washington, in which the Palouse Falls is found, was shaped by two major events in history. First was an enormous basaltic lava flow that occurred around 15 million years ago followed by massive flooding due to glacier outbursts around the area during the ice age (15,000 years ago).
This area is bound to the east by the Rocky Mountains, the south by the Basin and Range Province, and the west by the Cascades. The main tectonic structure in this area is the north-west-skewing Olympic-Wallowa lineament (OWL) that is partially a strike-slip fault and aligns with a number of anticlines found in the Yakima fold belt (Carson para. 7).
Between the Columbia River and the Blue Mountains, the OWL can be seen in form of a 200m high escarpment that marks out the Wallula fault zone; a chain of sharp pointed faults that show evidence of both dip-slip and strike-slip movements (Carson para. 7).
Another fault line, the Hite fault, crosses the OWL at almost 90 degrees southeast of Walla Walla, and disappears on the Lower Granite Dam on the Snake River. An earthquake of magnitude 6.0 was recorded in the area on July 15, 1936 (Bacon 68).
Works Cited
Alt, David. Glacial Lake Missoula and its Humongous Floods, Missoula, Montana: Mountain Press, 2001. Print.
Bacon, Charles R. “Eruptive history of Mount Mazama and Crater Lake caldera, Cascade Range, U S A.”, J Volc Geotherm Res, 18 (1983): 57-116.
Carson, Bob 2012, General Geology of Southeastern Washington. Web.