The video discription referenced a layer of "quick clay" as the cause. I'm no geologist but if you look on the left towards the end it looks like there are some waterfalls to me. Previous underground rivers/streams doing the deed.

The breathtaking scene occurred in Kraknes, Alta, on Wednesday morning. As eyewitness video shows, the land itself appeared to liquify and sweep the properties out to sea, churning the buildings in its path into rubble as they entered the water.