Mystery of the Megafloods

On one of our lab days, we watched an informational filmed called the Mystery of the Megafloods. The film began by defining what a geologist is, stating that it is similar to a detective looking for clues in a crime scene. A geologist looks at the rocks for clues in history.

The primary question that was evaluated in the film was what caused the bizarre landscape in the Montana region (the scad lands). It took us through the thought process of those scientists trying to figure out the cause.Some of the possible causes included gradual erosion caused by rivers and a giant river flooded over and over again. These were later ruled out because of the enormous potholes.
The last ice age was approximately 20,000 years ago. Another hypothesis was that the glaciers melted, causing a great flood. This, too, was soon ruled out because the ice was too remote.
The next hypothesis was that it was been the result of an enormous catastrophe, perhaps a giant flood. This was thrown out too.
The geologists had trouble determining the cause of the bizarre landscape because they were looking at eye view. No one thought to look from a different perspective until aerial photos were shown. The photos revealed giant ripples in the earth, ripples that resembled those in the sand at the beach.

The next hypothesis was that a glacier dammed the lake, forming the ripples. Glacial Lake Missoula formed as the Cordilleran Ice Sheet dammed the Clark Fork River just as it entered Idaho. The rising water behind the glacial dam weakened it until water burst through in a catastrophic flood that raced across Idaho, Oregon, and Washington toward the Pacific Ocean. This was the cause of the bizarre landscape.

For more information on the flooding of Glacial Lake Missoula and how the flooding occurred, click here.