Aim: To be able to understand when glaciers become a hazard, by focusing on the case of Lake Missoula.
Throughout the Earth's life the climate has fluctuated to temperatures even colder than today. This change in temperature can last for 2-10 million years and this is known as an ice age. There have been at least 5 major ice ages in the past and in the most recent advance the amount of glacial cover had reached its maximum cover and had almost all melted by 10 000 years. It was during this advance that the finger from the ice sheet moved southwards through the Purcell Trench, damning the Clark Fork river - therefore creating Lake Missoula.( See figure 1)
Figure 1: Map illustrating the location of Lake Missoula and the flood path it took (Source: Reference)
Soon the water started the build up behind the 2500 ft ice dam filled the valleys to the east creating a glacial lake the size of Lake Erie and Lake Ontario combined! The water continued to rise to 4200 ft, putting immense pressure against the dam until that castastrophic day when the dam could take no more pressure.
The ice failure gave way and released the volume of the Irish sea in glacial water in a shock wave tearing through the continent in 48 hours - destroying everything in its path. Making it was one of the largest floods in the history of the planet. The rate of flow of the water was SIXTY times that of the amazon and at 60mph and 100m high it cut 200m deep into the land. It took 10 hours for the flood full of debris to travel from the source to the ocean (the length of GB).
Look at the landscape it has left.....
Figure 1: Dry Falls, Washington (Source: Reference)
Figure 2: Frenchman Coulee, Washington (Source:Reference)
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