ACOUSTICAL WAVES, LONG-RUNOUT LANDSLIDES...
...and my hike last Thursday in Scottsdale AZ:
Much of my professional life is spent explaining to children how sound works - difficult because sound is tiny, invisible and nearly instantaneous.
But something you don’t know about me is that I’m a closet geology nut. I was a moderately hard-core hiker (when I had time for such things) and always wanted to know how the landscape in front of me was formed. So in reading up about the Phoenix area geology, where I was working last week, one of the factors mentioned that shaped the landscape were massive prehistoric landslides, and that there was a trail in the Mcdowell Mountain Sonoran Conservancy that explored a rare long-runout landslide - the Marcus Landslide. https://www.mcdowellsonoran.org/hike/marcus-landslide/
That jostled something in my memory - last year I had read a short precise of a scholarly article about a possible explanation for the mysterious long-runout landslides.
It’s a known fact that some landslides run nearly 20-30 times further than others. While there have been many explanations offered, when long-runout landslides were discovered on other planets and moons it ruled out water or air as a medium, and the geology - and physics - communities were left scratching their heads.
In 1995 a little-known paper by a researcher named Charles Campbell had discussed how simple particle flow could explain the phenomena. Building off that, in 2016 a group of researchers (Johnson et al) refined Campbell’s work and published a paper proposing that some landslides create vastly powerful acoustical waves that ripple through the debris (using the rocks as a medium), reducing friction and allowing the slides to travel much further. The process is called acoustic fluidization, where the sound actually acts like a lubricant. It’s kind of related to the soil liquefaction that can take place during earthquakes.
I think you can see where I am heading with this…
To me (admitted science nerd), this is an exciting example of one of the core nuggets of what I teach - sound waves and how they work. Since sound waves are so tiny and invisible, I’ve always tried to show kids big, visible manifestations of waves - like Galloping Gertie: the Tacoma Narrows Bridge that tore itself to pieces https://www.youtube.com/watch?v=j-zczJXSxnw.
And that’s why, when I finished work a bit early last Thursday, I hiked out to see the Marcus Landslide. I wanted to not only read about it, but go out and see it and touch it and walk around on it for myself. That is important for me, and a much, much, better story for kids. (Just sayin’, it’s a pretty cool site, and not a really long hike on a very easy trail with interesting interpretive signs explaining the landslide - but not about the acoustical waves, of course. Totally worth it.)
And now I feel I have another educational tool in my bag to use. Although this is still only in the research stage (only a couple of papers so far), as long as I’m clear about that I think just the possibility is going to blow kids’ minds.
Below are two links, one is an article in EOS, with a link to the newer scholarly paper - a for-pay link; and the other for the original ’95 paper, also for pay. Full disclosure, I didn’t pony up the bucks for either paper, although I suppose I should… but it’s going to lead me back to studying physics to try to understand the paper…yikes...
Wow, that was long. Does this mean I should start a blog? Sigh