Posted on 04/30/2016 9:34:37 PM PDT by fella
Very cool. That’s a flash flood from a very heavy rainstorm up river. They tend to pull all the junk laying in the river bed with them and form a sort of shell on top of the water.
Flash flood. Rocks carried on mud downstream. In SoCal mountains flash floods are quite common.
Where is this?
It’s a flash flood where the velocity of the water has reached over a supercritical flow rate, meaning it begins to scour the channel in which it flows.
This is combined with the slope of the channel, which allows the scoured material to continue with the flow and further scour as it flows downstream.
Those taking the video aren’t cognizant how precarious a situation they have placed themselves.
Once the bank is undermined, nothing would keep the boulders they are standing upon from adding to the flow.
Where was the video filmed? I don’t know. SoCal mountains have rain water flow from mountain storms down washes called arroyos. SoCal is basically desert. The arroyos are rock strune, dirt and 99% of the time dry washes. A mountain rainstorm brings water, mud, rocks, boulders and any other debris rumbling down these arroyos that can and do move cars, buildings just about anything in their way. Bridge washouts are not uncommon. As another poster commented, the water undercuts banks and any/all of that debris adds to the mix.
Very cool!
Is it accurate to term this a “lahar flow”?
Because that’s what we were told to call these as kids.
It is my understanding Lahar flows are caused by volcano activity. Rather than lava molten rock, lahars are mud and hot water mix. Flash floods are caused by rain water. NOTE: if Mt Rainer (Washinton state), blows again the main concern is a Lahar that would place Tacoma, pullayllup and that area in the path of a Lahar. Hope this helps.
Thank you for the info.
I remember Mt. St. Helens and the wall of burning mud that destroyed everything downstream. Would that then be a lahar flow?
I would say yes. It probably would be a Lahar flow.
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