The Importance of Salt in Quick Clay Landscapes

Salt binds clay together. When rain dissolves the salt, the clay becomes weak...

"Quick clay is typically originally deposited in a marine environment. In that environment, the positive charge of cations (such as Na²⁺) was able to bind clay particles with negative surface charge (typically silicates SO^-nn) by balancing charge in the double layer. When the clay became uplifted and was no longer subjected to salt water conditions, rainwater infiltrated these clays and washed away the salts that allowed these clay particles to remain in a stable structure.

With shear stress, the lack of counterbalancing charge from salts in the quick clay results in clay particle repulsion and realignment of clay particles to a structure that is extremely weak and unstable. Quick clay regains strength rapidly when salt is added, which allows clay particles to form complexes with one another."

https://en.wikipedia.org/wiki/Quick_clay

It looks a lot like soil liquefaction we see during earthquakes...spontaneous liquefaction...a new threat.. I wonder if they could have injected salt into the soil to prevent this from happening...weird stuff

Interesting video. There are other types of soil that have landslides as shown here.

The town where we live, Dalgety Bay, Fife sits on a thick clay strata, (like soft blue putty) as I discovered when digging out a pond in the garden. The town was created in 1970 so all the development is fairly recent. The area is roughly the same latitude as Rissa and the land is on a hill with a river estuary at the lower edge and lots of underground streams. You now have me worried!!!

I would be checking for salt content....and maybe check with your local geologist...

Interesting geology...

https://www.scottishgeology.com/wp-content/uploads/lfbg/LandscapeFashionedbyGeology-fifetayside.pdf