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This feedback cycle eventually weakened the ice dam so much that it could no longer support the pressure of the water behind it, and it failed catastrophically.
This process is known as a glacial lake outburst flood, and many such events have occurred in recorded history.
In the summer of 1922, and for the next seven years, Bretz conducted field research of the Columbia River Plateau.
He had been interested in unusual erosion features in the area since 1910 after seeing a newly published topographic map of the Potholes Cataract.
The peak flow of the floods is estimated to be 40 to 60 cubic kilometers per hour (9.5 to 15 cubic miles per hour).
Waitt's proposal was based mainly on analysis from glacial lake bottom deposits in Ninemile Creek and the flood deposits in Burlingame Canyon.
After analysis and controversy, geologists now believe that there were 40 or more separate floods, although the exact source of the water is still being debated.As the depth of the water in Lake Missoula increased, the pressure at the bottom of the ice dam increased enough to lower the freezing point of water below the temperature of the ice forming the dam.This allowed liquid water to seep into minuscule cracks present in the ice dam.His most compelling argument for separate floods was that the Touchet bed deposits from two successive floods were found to be separated by two layers of volcanic ash (tephra) with the ash separated by a fine layer of windblown dust deposits, located in a thin layer between sediment layers ten rhythmites below the top of the Touchet beds. By analogy, since there were 40 layers with comparable characteristics at Burlingame Canyon, Waitt argued they all could be considered to have similar separation in deposition time.The two layers of volcanic ash are separated by 1–10 centimetres (0.4–3.9 in) of airborne nonvolcanic silt. The controversy whether the Channeled Scabland landforms were formed mainly by multiple periodic floods, or by a single grand-scale cataclysmic flood from late Pleistocene Glacial Lake Missoula or from an unidentified Canadian source, continued through 1999.