Irregular reminder that landslides can behave like fluids.
(Thank you for all the pings!)
(Thank you for all the pings!)
https://twitter.com/rooneymobile/status/1327581502763380736
Landslides get weird when there really big, and can start behaving more like fluids than solids once they’re over the half million cubic meter mark.
...which was pretty much why I wrote a thesis once upon a time: io9.gizmodo.com/why-are-huge-l…
...which was pretty much why I wrote a thesis once upon a time: io9.gizmodo.com/why-are-huge-l…
But technically landslide are fluid-like, not fluids.
Why?
Because they’re a mixed mess of materials that act differently when moving than when still. You can’t just sample a tree trunk, some peat, and water to figure out the rheologic properties (how it flows).
Why?
Because they’re a mixed mess of materials that act differently when moving than when still. You can’t just sample a tree trunk, some peat, and water to figure out the rheologic properties (how it flows).
Consequence:
landslides may act like fluids, but are actually much more complicated physics that utterly defy our attempts at math.
So we shrug, call them fluid-like, and create imaginary model fluids that have the same bulk behaviour without trying to grapple with real dynamics
landslides may act like fluids, but are actually much more complicated physics that utterly defy our attempts at math.
So we shrug, call them fluid-like, and create imaginary model fluids that have the same bulk behaviour without trying to grapple with real dynamics
Of the fluid-like landslides, they can be fast or slow, wet or dry, laminar (smooth flow) or turbulent. Each of these is not just different properties, but different base equations of flow.
Figuring out what kind of model fluid to match to real landslide materials is Not Easy.
Figuring out what kind of model fluid to match to real landslide materials is Not Easy.
Rock avalanches like Frank Slide, BC or sand avalanches like you collapse on dunes usually get modeled as frictional fluids.
Debris flows tend to model as turbulent Voellmey fluids.
Clay-rich flows tend to be plastic-sticky Bingham fluids. That’s my first guess for peat.
Debris flows tend to model as turbulent Voellmey fluids.
Clay-rich flows tend to be plastic-sticky Bingham fluids. That’s my first guess for peat.
https://twitter.com/mikamckinnon/status/1104850704160751617
Clues for trying to figure out what type of fluids most closely matches this landslide:
1. It’s relatively slow. You could run away from it, maybe even briskly walk.
2. It’s smooth/laminar: those trees are staying upright.
3. It’s flowing down a very low angles slope.
1. It’s relatively slow. You could run away from it, maybe even briskly walk.
2. It’s smooth/laminar: those trees are staying upright.
3. It’s flowing down a very low angles slope.
This peat failure is NOT a quickclay slide.
Quickclays happen in former ocean floors where salt is integrated into the clay. Water or weight collapses the structure, triggering a landslide.
Both result in big slow dramatic flows, but are fundamentally different cause & dynamics
Quickclays happen in former ocean floors where salt is integrated into the clay. Water or weight collapses the structure, triggering a landslide.
Both result in big slow dramatic flows, but are fundamentally different cause & dynamics
https://twitter.com/mikamckinnon/status/1268554984397967372
All big landslides are weird in their own special ways. Peat’s oddities:
1. It’s light. Like, half the density of water. That raft of trees is probably floating.
2. It compresses easily, but has lots of tensile strength: rafts hold together.
gov.scot/binaries/conte…
1. It’s light. Like, half the density of water. That raft of trees is probably floating.
2. It compresses easily, but has lots of tensile strength: rafts hold together.
gov.scot/binaries/conte…
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