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Grand Coulee breach site 15,600 years ago

View on map:47.938758°N 119.010241°W

Comments

"Here, the Grand Coulee hit its breaching point (probably arond 15.6kya), sometime after the Okanogan lobe of the Cordilleran Ice Sheet had advanced far enough to dam the waters and form Glacial Lake Columbia. The Okanogan Lobe advanced far enough across the Waterville plateau during the Glacial Maximum ~18-15.4kya to dam up Glacial Lake Columbia to about 2400-2500ft asl, this would eventually carve the Grand Coulee system. " (see reference).

Description


Location of Glacial Lake Columbia in Washington, USA.

Glacial Lake Columbia was the lake formed on the ice-dammed Columbia River behind the Okanogan lobe of the Cordilleran Ice Sheet when the lobe covered 500 square miles (1,300 km) of the Waterville Plateau west of Grand Coulee in central Washington state during the Wisconsin glaciation.[1] Lake Columbia was a substantially larger version of the modern-day lake behind the Grand Coulee Dam. Lake Columbia's overflow – the diverted Columbia River – drained first through Foster Coulee, and as the ice dam grew, through first Moses Coulee, and finally, the Grand Coulee.[2][3]

References

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