Ancient cataclysmic floods -- erratics from Lake Missoula drainage events

 

A nice little gallery of erratic pics from YouTube videos on the topic of the Missoula floods.  More info here:

https://www.nps.gov/iafl/index.htm

https://volcanoes.usgs.gov/observatories/cvo/Historical/LewisClark/Maps/map_missoula_floods.shtml

https://en.wikipedia.org/wiki/Missoula_floods

The floods (maybe as many as 100 flood "events" during the Quaternary) were all cataclysmic in the best sense of the word, but naturally we know most about the latest series of meltwater outbursts at thge end of the last (Wisconsin) glacial episode.    Many of the giant erratics are well over 100 km from their source areas.  Many were incorporated in glacier ice and swept away in icebergs following the collapse of each successive ice dam -- these have many of the diagnostic characteristics of typical glacial erratics.  They are often sub-rounded or sub-angular.  But others are angular or sharp-edged, suggesting they they were literally ripped away from the bedrock by the force of the water, armed as it was with abundant fragments of glacier ice.