Palouse Falls: The Receding Falls

The breathtaking falls in front of you formed from a series of cataclysmic events. The Palouse Falls stands at 197 feet tall and is the product of several geologic phenomena that are prevalent in the Columbia Plateau.

The Palouse River slowly eats away at the basalt landscape, but it alone would not have been able to make the sheer cliffs and large plunge pool you see. The basalt in the area of the Palouse Falls has been fractured by the fault zones (Griggs, 1973; Reidel, 2013). The basalt also has many smaller fractures and joints that formed as the magma cooled. The numerous fractures and joints make it brittle and easy for water to get inside and erode away at the basalt, especially when the water comes in torrential rages, such as the Missoula floods. The Palouse River’s path is guided by the fractures upstream of the falls. The falls themselves are created from the waterfall, or cataract, plucking away at the bottom cliff the channel flows over. This plucking over time eats away the underside of the cliff until there is a failure of the top ledge, which pushes the waterfall back. The process repeats many times, and a receding waterfall is created (Fig. 1). Figure 2 shows that the Palouse Falls retreated 32,800 feet, or about 6.2 miles, along the Palouse River from the Snake River (measured on Google Earth).

The glacial outbursts from Lake Missoula Floods played a huge part in the carving out of the Palouse falls. When you look at the falls they look small compared to the large pool that they flow into (Fig. 3). In fact the falls you are looking at converted many disbelievers of the catastrophic floods, due to the size of the plunge pool and the relatively tiny river that now cascades. As you watch the waterfall and admire the canyon that the river runs through, just try to imagine how powerful the outburst floods from Lake Missoula must have been to carve such a magnificent feature.

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