Ice dam hypothesis

Let’s take a look at the ice dam hypothesis.

Sometimes a glacier flows down a valley to a confluence where the other branch carries an unfrozen river. The glacier blocks the river, which backs up into a lake, which eventually overflows or undermines the ice dam, suddenly releasing the impounded water.

A glacier created an ice dam on the Clark Fork River that created Glacial Lake Missoula.

It’s estimated there were 500 cubic miles of water was behind the ice dam. (The volume of Lakes Erie and Ontario combined.) … 2/sec3.htm

The ice dam was also more than 2000 feet tall.

2000 feet tall is not a trivial height. This is about 2 Eiffel towers stacked on top of each other. And 500 cubic mile of water is no small matter either. For a comparison, the largest dam in the world, the Three Gorges dam, is 630 feet high and holds 51,402,459 cubic yards of water. Whereas the Glacial Lake Missoula would’ve held 2,725,888,000,000 cubic yards. That’s 53000 times the volume of Three Gorges dam.

As the lake basin drained, the water had to pass through narrow parts of the Clark Fork Canyon where current velocities are calculated to have reached 45 miles per hour. The maximum rate of flow is estimated to have been 9-1/2 cubic miles per hour – a rate of 386 million cubic feet per second, or about 10 times the combined flow of all the rivers of the world. For comparison, the rate of flow of the world’s largest river, the Amazon, is 6 million cubic feet per second, and the Columbia averages about 255 thousand cubic feet per second. … 2/sec4.htm

The entire 500 cubic mile of water is estimated to have been emptied in 2 to 3 days. … appen.html

An ice dam with a depth of 2000 feet does not form quickly. One question is how could it’ve formed to this depth over time without the hydrostatic pressure of water to collapse it before it got to be so large? All ice dams we see today collapse far below this size. For example, the Hubbard Glacier released 1.27 cubic mile of water on Oct 8, 1986.

And for any hydrologists out there, is it even theoretically possible to create an ice dam this large without it collapsing before then?


jwu wrote:Your figure is the volume of the dam construction, not of the water that is held behind it. The actual amount of water is roughly 39 cubic miles, so the ice dam doesn’t hold 53000 times but only about 12 times as much water.

Ah, thank you for the correction. :)


jwu wrote: Note that the actual volume of the lake is irrelevant to the pressure, only the height of the dam matters.

This is one of the problems I see with the ice dam hypothesis. Someone is going to have to prove to me that ice alone can hold back water that is 2000 feet high. Even if it was created by a continent sized glacier, it would still have this problem.

The largest dam we’ve created with steel and concrete is 630 feet tall, so how can ice create a dam over 3 times in height and hold back that much pressure?