How are mountains made? The origins of local relief in the North Cascades
The Wenatchee Valley Erratics next Zoom program will be on Tuesday, April 12 at 7:00 PM. Dr. Ralph Haugerud, USGS/UW, will discuss, “How are mountains made? The origins of local relief in the North Cascades.”
Mountains are made by uplift and erosion. In the North Cascades, folding, faulting, and granite intrusions thickened the crust about 105-50 million years ago. But the associated uplift probably eroded away fairly quickly. Volcanic activity created some modern high elevations, such as Mt Baker and Glacier Peak. Up-folding built other high areas, such as the Naneum Ridge anticline, which extends to the northwest through the Mt Stuart massif. Regional uplift probably has deeper causes.
While we hypothesize the causes of uplift, the story of erosion is more obvious. Exceptional local erosion in the North Cascades points to several different events:
◦ Breaching of divides by meltwater ponding in front of the Cordilleran ice sheet and carving deep slots (e.g., Skagit Gorge, Lost River Canyon);
◦ Channeling of meltwater at the edge of the ice sheet (Sinlahekin Coulee);
◦ Supplementation of local alpine glaciers by Cordilleran ice (Chelan and Methow troughs);
◦ More-intense alpine glaciation in the Icicle Creek drainage, fed by the high ground of the Naneum uplift.
Thus are (some) mountains made.
Zoom link: https://us02web.zoom.us/j/84812873290?pwd=ZlBnMHVDWmtYNEJHQ283V1kxWXA1QT09
Passcode: erratics
Please sign in at 7:00 PM, April 12!
Contact information:
Brent Cunderla, Chapter President
(509) 860-6067