Missoula Floods - Flood Events

Flood Events

As the water emerged from the Columbia River gorge, it backed up again at the 1 mile (1.6 km) wide narrows near Kalama, Washington. Some temporary lakes rose to an elevation of more than 400 ft (120 m), flooding the Willamette Valley to Eugene, Oregon and beyond. Iceberg rafted glacial erratics and erosion features are evidence of these events. Lake-bottom sediments deposited by the Missoula Floods are the primary reason for the agricultural richness of the Willamette Valley.

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. 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). The maximum flow speed approached 36 meters/second (130 km/h or 80 mph). Up to 1.9×1019 joules of potential energy were released by each flood (the equivalent of 4,500 megatons of TNT). The cumulative effect of the floods was to excavate 210 cubic kilometres (50 cu mi) of loess, sediment and basalt from the channeled scablands of eastern Washington and to transport it downstream.