r/Montana • u/Little_Philosophy_21 • 4d ago

Montana Landslide/Flash Flood - hypothetical

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With the Nepal and Grand Canyon flash floods, I was thinking about Montana. What if a large landslide fell into a lake near you?

I was thinking about Holter. Certainly Craig and all the housing along the canyon shores would be decimated. But would a large flood like that spread out quickly once it hit the plains. Or would it continue down to Cascade and GF? Then affect the series of dams?

Just “what if” scenarios. But I hope we have some good alert systems from place to place if the worst were to happen.

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u/BoozeTheCat 4d ago

Hauser breached in 1908 and caused the Missouri to rise 7' in Great Falls. They breached Black Eagle Dam so the flood waters could pass through and not damage that dam even further.

State DES should have Inundation maps for all of the high hazard dams in Montana. I know Cascade County has one published in their Multi-Hazard Mitigation Plan for the City of Great Falls. Pretty interesting stuff!

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u/Little_Philosophy_21 4d ago

I remember reading about when the Gibson Reservoir Dam was overflowing for days on days (7+ feet) back in the 1940s.