The landscape of the Pacific Northwest has been significantly shaped by massive floods in the geologic past. Beginning approximately 17 million years ago, the broad lava flows of the Columbia River Flood Basalts poured forth from widespread fissures near the borders of Washington, Oregon, and Idaho. An estimated 160,000 km3 of basalt was emplaced, mostly within a million-year span centered around 16 million years ago. Anyone traveling the Columbia River Gorge by ship or car can appreciate the voluminous nature of these flows, representing over 300 individual eruptions. Geologist Kirt Kempter explores the likely connection of these eruptions with the Yellowstone hot spot, along with a trail of supervolcano eruptions across southern Idaho.
Kempter fast-forwards to the end of the last Ice Age cycle, in which flooding again sculpted the landscape of the Pacific Northwest—although this time it was water, not lava, that claimed responsibility. The vast Lake Missoula, formed by an ice dam from the Cordilleran Ice Sheet, catastrophically breached the dam and poured across the central and eastern Washington region, scouring the flood basalt province and carving much of the Columbia River Gorge. The scenario would then repeat, as there is evidence for more than 100 of these breached ice-dam floods.
Almost synchronously, another Ice Age lake in Utah, Lake Bonneville, produced a catastrophic flood that emptied into the Columbia River, creating its own scoured landscape along the Snake River in southern Idaho. Kempter uses maps, diagrams, and Google Earth images to help tell these amazing stories of flooding.
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