The eruption of Glacial Lake Missoula created Washington state's trough scab fields. In southeastern Washington state, a neat grid of farmland stretches for miles over gently rolling hills. Dozens of different crops are grown on the Colombian Plateau's precious farmland. In some places, however, undulating streaks of washed earth interrupt the angular plots and central pivot-irrigated fields.
These rock scars, known as Channeled Scarlands, were formed during a series of major floods 10,000 to 20,000 years ago. On May 14, 2023, Landsat 8's OLI (Ocean Land Imager) imaged part of the scab about 120 kilometers (75 miles) west of Spokane.
For decades, geologists were kept in the dark about the water sources that carved these unusual landforms. They later learned that during the last ice age, the Cordillera Ice Sheet formed a dam along the Clark Fork River as it advanced southward. Missoula Glacial Lake grew just behind this ice dam in what is now western Montana, eventually holding as much water as Lakes Erie and Ontario combined.
Geologists estimate that over the course of thousands of years, the dam formed and ruptured dozens of times, with each breach tearing as much as 600 cubic miles of water across the region.
Floodwater flows to the south and southwest, eventually joining the Columbia River. Along the way, floodwaters carved grooves, pits and long channels called "coulees" into the volcanic basalt bedrock. The image above shows a detail of one of the river channels, revealing the stark contrast between flooded areas and arable land.
The canyon shown here is insignificant compared to Great Curry Canyon, which is the largest canyon in the Channeled Scablands to the north of this map. Completed in 1942, the Grand Kuri Dam was once the world's largest concrete structure, surpassed by the Itaipu Dam in South America in 1984 and the Three Gorges Dam in China in 2006. It remains the largest hydroelectric facility in the United States and provides irrigation water to the Columbia Plateau.
Image from NASA's Earth Observatory, taken by Lauren Dauphin using Landsat data from the U.S. Geological Survey.
Compiled source: ScitechDaily