MEGAFLOODS AND CLOVIS CACHE AT WENATCHEE

Immense late Wisconsin floods from glacial Lake Missoula drowned the Wenatchee reach of Washington’s Columbia River valley by different routes. Early flood(s) nearly 19,000 cal yr BP, raged 335 m deep down the Columbia and built high-level Pangborn bar at Wenatchee. As advancing ice blocked the northwest reach of Columbia valley below Okanogan valley, several giant floods descended Moses Coulee and backflooded up the Columbia past Wenatchee. Ice then blocked Moses Coulee, and Grand Coulee to Quincy basin became the westmost floodway. From Quincy basin, many Missoula floods backflowed 50 km upvalley to Wenatchee 18,000 to 15,500 years ago. Receding ice dammed glacial Lake Columbia for centuries more—till it burst about 15,000 years ago. After Glacier Peak ashfalls about 13,600 years ago, smaller great flood(s) swept down the Columbia apparently from glacial Lake Kootenay in British Columbia.

The East Wenatchee cache of huge fluted Clovis-culture points had been laid atop Pangborn bar after the Glacier Peak ashfall, and then they were gradually buried by loess. The Clovis people arrived five and a half millennia after the early gigantic Missoula floods. This was some two and a half millennia after the last small Missoula flood and two millennia after the glacial Lake Columbia flood. Yet early people likely saw outburst flood(s) from glacial Lake Kootenay about 13,000 years ago.