Smaller mountain landslides do occur in modern times. There was one here in Montana in 1959 that killed 27 people and blocked a major river. The effects are still visible today.
>Between 50 and 48 million years ago a sheet of rock about 500 square miles (1,300 square kilometers) in area detached from the plateau south of the Beartooths and slid tens of kilometers to the southeast and south into the Bighorn and Absaroka Basins
Luckily events like this are geologically rare. A bigger risk would be tsunamis from underwater mountain landslides.
https://en.wikipedia.org/wiki/Heart_Mountain_(Wyoming)
>Between 50 and 48 million years ago a sheet of rock about 500 square miles (1,300 square kilometers) in area detached from the plateau south of the Beartooths and slid tens of kilometers to the southeast and south into the Bighorn and Absaroka Basins
Luckily events like this are geologically rare. A bigger risk would be tsunamis from underwater mountain landslides.