Pro tip for people moving north; don't buy land in the valleys around Mt. Rainier. This type of flood (also known as a lahar) has occurred there many times. The mudflows reached the harbor of Tacoma in the past. [0] I expect we'll see at least one new one in our lifetime, as the glaciers have been greatly affected by rising temperatures.
[0] https://www.usgs.gov/media/images/mt-rainier-lahar-hazard-ma...