Geologist wanders through and discusses land slides from Helene
 

Interesting video

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I got my Master's degree in engineering geology at Imperial College, London. My thesis was on a large debris flow in Wales on the eastern flank of Mount Snowden, with a new method to predict them based on geologic and various other conditions. So this video was very interesting for me. Textbook debris flows. Thanks for the post.

Cool. I thought it was interesting. I just want to know when the next book is coming out. ;) :D

If it is not called, "Debris Flow", I ain't buyin':cool:

I enjoyed the video while having zero point of reference other than I know water.

Is a debris flow like the subject of the video similar to a pyroclastic flow? A lot of what he was talking about sounded like the kind of stuff that I think I've heard about those.

They're kind of the same. They both move quickly and destructively downslope. But the initiating mechanisms and reasons for entrainment are different. For a debris flow to mobilize, the soil needs to have a fair amount of coarser material, like sand and gravel. You need excess pore pressures to get the whole thing moving. They typically are triggered during very intense rainfall over a short period of time, after a prolonged period of merely heavy (not intense) rainfall. Helene was certainly that.

Just watched the video, thanks for posting it.
That must have been a massive amount of mud and debris to take out that much area of the stream bed. I'd always been warned about the dry creek beds out in the desert becoming flooded in a hurry from storms that were miles away. I bet this was similar only it had more 'stuff' in it than just water alone. I wonder what the area at the 'end of the line' looks like now. Must be a royal mess I bet.

Interesting, the specifics of the triggers. Thanks. Some of the details that the guy mentioned in the video were interesting. the flaky rocks, the water in the soil, etc...

What triggers a pyroclastic flow? :D

I'm assuming that the stuff gets spread out by the massive amounts of water. I'm assuming that at the bottom, it seems like less stuff, but is spread over a huge area.