Jun 4th 2020,
19 tweets,
8 min read
Q: Whoa. What’s happening?!
A: This is a quickclay landslide.
Everyone is ok, even the dog. The science is spectacular in an unnerving sort of way.
A: This is a quickclay landslide.
Everyone is ok, even the dog. The science is spectacular in an unnerving sort of way.
Quick clays are deposited in marine environments, which means the minerals incorporate salts to create a fragile cardhouse structure.
Add water that washes away the salt and... it all collapses.
Add water that washes away the salt and... it all collapses.
Quickclays are part of the sensitive clays that you need to handle very, very carefully.
They’ll also collapse if you add too much weight on top of them (load them too much).
What does collapse look like? When a solid clay just kinda oozes into a goop & flows away:
They’ll also collapse if you add too much weight on top of them (load them too much).
What does collapse look like? When a solid clay just kinda oozes into a goop & flows away:
Norway (& eastern Canada!) has a lot of quickclay.
The 1978 Rissa quickclay disaster is beyond fascinating, and was triggered by weight of a freaking tiny 700m3 earth dam.
Video (yes, those are houses flowing past):
Report: issmge.org/uploads/public…
The 1978 Rissa quickclay disaster is beyond fascinating, and was triggered by weight of a freaking tiny 700m3 earth dam.
Video (yes, those are houses flowing past):
Report: issmge.org/uploads/public…
Norway knows it has quickclays. They’ve had an extensive mapping program since 1980 and keep getting better at it.
Hazard ID: ngu.no/en/topic/quick…
Hazard mapping: ngu.no/en/topic/mappi…
Improved methods: link.springer.com/chapter/10.100…
Hazard ID: ngu.no/en/topic/quick…
Hazard mapping: ngu.no/en/topic/mappi…
Improved methods: link.springer.com/chapter/10.100…
But large-scale mitigation of quickclay is... challenging.
Adding wells to inject potassium chloride (sylvite, a lickable mineral cousin of halite) seems to make quickclay less sensitive: nrcresearchpress.com/doi/full/10.11…
Mitigation would be expensive & difficult: aimspress.com/article/10.393…
Adding wells to inject potassium chloride (sylvite, a lickable mineral cousin of halite) seems to make quickclay less sensitive: nrcresearchpress.com/doi/full/10.11…
Mitigation would be expensive & difficult: aimspress.com/article/10.393…
More often, we realize we already built on quickckay.
Retroactive hazard identification is a bit like realizing you’re precariously balanced on a house of cards. You didn’t trigger collapse yet, but building more might.
Lyngseidet triggered by loading 📷 Andrea Taurisano, NVE
Retroactive hazard identification is a bit like realizing you’re precariously balanced on a house of cards. You didn’t trigger collapse yet, but building more might.
Lyngseidet triggered by loading 📷 Andrea Taurisano, NVE
The residents of this coastal cottage spotted tension cracks the night before, but didn’t realize they meant the ground was slowly pulling apart.
When the landslide started, they ran. Quickclays move slowly enough that they made it to safety.
📷 Jan Egi Bakkeby
When the landslide started, they ran. Quickclays move slowly enough that they made it to safety.
📷 Jan Egi Bakkeby
Initial reports estimate the landslide is 600m wide x 40m deep. Length is difficult to judge size since quickclay flows & spreads, but it’s in the 1-10 million cubic meters range.
Landslides have human-centric speed classification. Faster than walking but you can outrun? Rapid.
Landslides have human-centric speed classification. Faster than walking but you can outrun? Rapid.
If this is looking familiar, I did a shorter & more incoherent version last night.
Turns out I’m shit at explaining geology when distracted by hoping police won’t violently explode on protestors. Humans scare me more than rocks.
Turns out I’m shit at explaining geology when distracted by hoping police won’t violently explode on protestors. Humans scare me more than rocks.
Dave has several stills from the video:
Q: Could they have just... pinned the house in place? Deeper foundations, more pipes, something?!
A: Nope.
1. Every structure would be more load that could’ve destabilized it sooner.
2. The clay collapsed. The ground was behaving like a fluid, not a solid. You can’t pin fluids.
A: Nope.
1. Every structure would be more load that could’ve destabilized it sooner.
2. The clay collapsed. The ground was behaving like a fluid, not a solid. You can’t pin fluids.
Q: Is quickclay simuler to liquefaction or quicksand?
A: Nope! Liquefaction is when saturated sediment is agitated (like by an earthquake), jiggling grains to be more tightly packed.
Quicksand is liquefaction in saturated sand, like by bouncing on a wet beach.
A: Nope! Liquefaction is when saturated sediment is agitated (like by an earthquake), jiggling grains to be more tightly packed.
Quicksand is liquefaction in saturated sand, like by bouncing on a wet beach.
Q: Um. You mentioned Canada...?!
A: Anywhere coated in former ocean floor mud potentially has quickclay.
In Canada, that’s mostly the Leda clays around thé now-gone Champlain Sea, although we’ve got small stranded marine terraces in the Rockies.
📷 Natural Resources Canada
A: Anywhere coated in former ocean floor mud potentially has quickclay.
In Canada, that’s mostly the Leda clays around thé now-gone Champlain Sea, although we’ve got small stranded marine terraces in the Rockies.
📷 Natural Resources Canada
Bonus context note:
This landslide was documented by Jan Egi Bakkeby. That’s his video.
The same Bakkeby whose home is falling into the ocean.
The same Bakkeby who fled & ran to safety when the landslide started.
That’s why the video starts partway through the landslide.
This landslide was documented by Jan Egi Bakkeby. That’s his video.
The same Bakkeby whose home is falling into the ocean.
The same Bakkeby who fled & ran to safety when the landslide started.
That’s why the video starts partway through the landslide.
Q: Was this landslide related to sea level rise or permafrost melt or...?
A: Unlikely. The ground was inherently unstable. It collapsed because of its structure, not wave attack from below
Exact trigger may never be known, but it’s often as simple as moving around piles of dirt
A: Unlikely. The ground was inherently unstable. It collapsed because of its structure, not wave attack from below
Exact trigger may never be known, but it’s often as simple as moving around piles of dirt
After a lot of confusion yesterday, folks helped me figure out @NVE is Norway’s Water & Energy agency.
Their initial investigation points at recent rapid melt of heavy snowpack saturating the ground. That influx of freshwater could’ve dissolved salt, triggering the landslide:
Their initial investigation points at recent rapid melt of heavy snowpack saturating the ground. That influx of freshwater could’ve dissolved salt, triggering the landslide:
8 buildings were destroyed by the landslide:
1 full-time home
3-4 holiday homes (translation unclear)
Remainder boathouses & outbuildings
1 full-time home
3-4 holiday homes (translation unclear)
Remainder boathouses & outbuildings
Wee tsunami, like ripples from throwing pebbles in a pond but bigger because it’s a few million cubic meters of ground into the ocean:
