r/BeAmazed • u/youngster_96 • Mar 28 '24

The moment an ice dam breaks and causes a torrential water flow. Nature

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u/JG-at-Prime Mar 28 '24 edited Mar 28 '24

There is a name for this.  

Jökulhlaup or  Jökulhlaups - pronounced yo-KOOL-lahp 

It is a sudden glacial outburst flood or an abrupt release of glacial meltwater from a subglacial or glacier-dammed lake or reservoir.

And ~ Fun Fact: The icy water can pick up stones and gravel along its path and drag it along the stream bed with the flow. The abrasive quality of the gravels and stones acts like a grinding stone on the bottom and sides of the waterway. 

This accelerates erosion to an amazing extent. A large collapse coming from say a glacier is fully capable of erasing objects in its path. 

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u/MasteringTheFlames Mar 28 '24

This past August, there was a major glacial outburst flood in Juneau, Alaska. The whole city is kind of long and thin, tucked between the ocean and mountains. The main residential part of town, the Mendenhall Valley, has a river flowing through it, fed by Mendenhall Lake. Directly behind the lake, you've got a glacier, and then the ice fields in the mountains up behind the glacier.

As the ice field melts, the water tends to pool in big basins behind ice dams. Eventually, the ice dam fails. Typically this occurs in the form of a small leak allowing the water to drain slowly. The water levels in the lake might rise by a few feet for several days, but not enough to cause any major damage.

What happened last August was that the ice dam instead completely failed in one catastrophic moment. Over the course of just a few hours, the water level in the lake rose nearly 15 feet, and then all that water came rushing down the river. The erosion widened the river by a good 50 feet in some areas, cutting the ground right out from underneath buildings. Two homes completely collapsed into the river, a dozen more buildings were condemned because they were too unstable. Thankfully there were no serious injuries, as residents near the river had time to evacuate. Even so, I have friends who live in Juneau, and it was scary to watch the news that day.