Granular Flow

One of the most notable granular flow rockslides is the Mount St. Helens debris avalanche of May 18, 1980, which became the largest landslide in recorded history.

Triggered by a magnitude 5.1 earthquake, the volcanic flank collapsed, releasing around 2.8 cubic kilometers of rock, ice, and sediment in a massive granular flow.

This slide traveled at speeds exceeding 150 km/h (93 mph), covering an area of roughly 60 square kilometers and permanently reshaping the surrounding landscape.

Its scale and speed provided critical insights into granular flow mechanics, influencing how geologists model large rockslide and debris flow events worldwide.