Friday, November 27, 2015

Stubbed Toe

See below; this is my reconstruction of the Santa Clarita landslide.

Typically large, slow-moving rotational slump- (meaning that the movement is rotational, with the top part moving down and in and the bottom (or toe) moving down and out) earthflows (meaning that the thing is moving slowly, like a big earth glacier) develop large toe-bulges at the bottom. Somewhere in my files I have a picture of an old mine access road that has been buckled up and rotated vertical by the toe pushing up and out at the bottom of a large earthflow; the thing stood straight up for about 8 or 10 feet. That'd have been a real sonofabitch to drive up with a stick shift.

I had a long discussion about this thing with my friend GeoChick, and I told her my problem was that all the articles had the scientific intelligence of a mophead. "Guh - landslide" was about the level of sophistication. Seriously; I couldn't tell either from the pictures or the text enough about the topography or the geology to even guess what was happening.

But long-time commentor Ael finally sent me a link to an article that showed not just the big honkin' road uplift but the surroundings, and it looks pretty clear to me that this thing is at or near the base of a slope that is failing, and it's pushing this road up because the road is at or near where the bottom of the slide plane "toes out" of the ground surface...

And this is a simple landslide. Given that, can you imagine how hard it is for most reporters to understand something as complex as climate change?


Ael said...

Sweet. Thanks Chief!

For some reason, I had always thought that slump meant down.
But if you look at the ground as some sort of funny mix between liquid and solid you can see how the pressurized ground (by all the dirt sitting on top of it) could push upwards a bunch of non-pressurized dirt as everything moves around trying to equalize pressure.

Of course, once you start looking at the dirt as a liquid then you get the full complexities of plumbing because pressure can travel long distances and where the pipe fails isn't always close to where the pipe got plugged up.

Nice field you have there, Chief. Always lots of puzzles to solve.

Ael said...

Oh, one more thing (and because I love trolling), did you notice that the link was Russian?

Strange how the Evil Empire's propaganda site provided better information (and a lovely drone video) than Freedom's news organizations.

FDChief said...

I should have specified that I think this is a "rotational" slump; in a rotational failure the driving force rotates around a horizontal axis. The top drops down as a block and rotates, while the bottom (the toe) gets pushed up and out. Typically the whole thing isn't really driven by "pressure" as gravity. When the driving force - the mass of the upper portion of the slope times the gravitational acceleration (F = ma, right?) overcomes the resisting force (the internal friction of the material (what we call "phi" after the greek letter) plus the cohesion) then you get movement.

The deformation typically doesn't move as a fluid except in extreme cases such as debris flows or mudflows; you can model it as a solid block even though the actual soil probably behaves somewhere between a solid and a plastic.

The difference between the two coverages probably has to do with the pernicious profit-taking aspect of capitalist "news" combined with a distance from the event. Since the public wants - or, at least the media corporations seem to believe the public wants - "infotainment" US news coverage tends to go for the simple and stupid. The Russians don't have any reason to see this as "news", so for them its more academic, perhaps, hence the reduced need to show up-close scary pictures of heaving roads...