The Channeled Scablands are a relatively barren and soil-free region of interconnected relict and dry flood channels, coulees and cataracts eroded into Palouse loess and the typically flat-lying basalt flows that remain after cataclysmic floods within the southeastern part of Washington state. The Channeled Scablands were scoured by more than 40 cataclysmic floods during the Last Glacial Maximum and innumerable older cataclysmic floods over the last two million years. These floods were periodically unleashed whenever a large glacial lake broke through its ice dam and swept across eastern Washington and down the Columbia River Plateau during the Pleistocene epoch. The last of the cataclysmic floods occurred between 18,200 and 14,000 years ago.
Geologist J Harlen Bretz defined "scablands" in a series of papers written in the 1920s as lowlands diversified by a multiplicity of irregular channels and rock basins eroded into basalt. Flood waters eroded the loess cover, creating large anastomizing channels that exposed bare basalt and creating butte-and-basin topography. The buttes range in height from , while the rock basins range from in width up to the long and 30 m deep Rock Lake. Bretz further stated, "The channels run uphill and downhill, they unite and they divide, they head on the back-slopes and cut through the summit; they could not be more erratically and impossibly designed."
The debate on the origin of the Scablands that ensued for four decades became one of the great controversies in the history of earth science. The Scablands are also important to planetary scientists as perhaps the best terrestrial analog of the Martian outflow channels.
Bretz conducted research and published many papers during the 1920s describing the Channeled Scablands. His theories of how they were formed required short but immense floodsfor which Bretz had no explanation. His theories of apparent catastrophism met with vehement opposition from geologists of the day, who tried to explain the features with uniformitarian theoriesthat they were shaped by processes still acting today.
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The Missoula floods (also known as the Spokane floods or the Bretz floods or Bretz's floods) were cataclysmic glacial lake outburst floods that swept periodically across eastern Washington and down the Columbia River Gorge at the end of the last ice age. These floods were the result of periodic sudden ruptures of the ice dam on the Clark Fork River that created Glacial Lake Missoula. After each ice dam rupture, the waters of the lake would rush down the Clark Fork and the Columbia River, flooding much of eastern Washington and the Willamette Valley in western Oregon.
In geology, catastrophism theorises that the Earth has largely been shaped by sudden, short-lived, violent events, possibly worldwide in scope. This contrasts with uniformitarianism (sometimes called gradualism), according to which slow incremental changes, such as erosion, brought about all the Earth's geological features. The proponents of uniformitarianism held that the present was "the key to the past", and that all geological processes (such as erosion) throughout the past resembled those that can be observed today.
The Channeled Scablands are a relatively barren and soil-free region of interconnected relict and dry flood channels, coulees and cataracts eroded into Palouse loess and the typically flat-lying basalt flows that remain after cataclysmic floods within the southeastern part of Washington state. The Channeled Scablands were scoured by more than 40 cataclysmic floods during the Last Glacial Maximum and innumerable older cataclysmic floods over the last two million years.