This is a drone video of the landslide that occurred in Alta, Norway earlier this week. No one was hurt, and even a dog was rescued after it was able to swim back to shore.
This type of slide is thought to occur on a "Quick Clay" layer, produced as the glaciers departed at the end of the last glaciation. 15,000 years ago - Norway and Scandinavia were covered by a gigantic ice cap. The weight of this ice cap actually pressed down the Earth's crust - like using your hand to push a toy down to the bottom of the bathtub.
When the glaciers melted, the ocean returned, flooding the land you see above the water today. Those ocean waters deposited thin layers of clay and salt on the newly-submerged landscape. But, as the weight of the glaciers was also removed, the land began popping up, bringing this thin layer of ocean sediments above the surface. For the last 10,000 years, sediment from the land buried this thin clay layer, and now houses are constructed on some parts of that landscape. Today, it sometimes only takes a small event, like a rainstorm that dissolves some of the salt, to make that clay layer weak enough to trigger a slide.
