Steven Dutch, Professor Emeritus, Natural and Applied Sciences, University of Wisconsin - Green Bay
Location: 48o 16' 02" N, 012o 19' 45" E.
As the reservoir neared full, there were numerous indications that the mountain slope was becoming unstable. The deep gorge meant that there was nothing at the bottom to hold the valley walls in place except the friction between rock layers. Filling of the dam did three things to make the mountainside even more unstable. First, the water supported some of the weight of the rock. Second, water seeped into the weak rock layers, weakening them further and making them slipperier. Third, water deep in the reservoir was under a great deal of pressure, so water within the adjacent rocks was also under pressure, helping to lift the overlying rocks.
By September, 1963 it was becoming obvious that the mountainside was going to slip and the dam owners began lowering the water level in the reservoir. In October, heavy rains soaked the rocks on the mountainside, weakening the weak layers even more. Finally, at 10:38 P.M. on October 9, 1963, the mountainside gave way.
Return to Geology Coloring Book Index
Return to Professor Dutch's Home Page
Created 8 October 2009, Last Update 15 January 2020