Large scale landslide deposits have been found off the coast of several Hawaiian islands including Molakai and the big island of Hawai'i. A debris avalanche is formed when an unstable slope collapses and debris is transported away from the slope. Large scale avalanches normally occur on very steep volcanoes. A cold debris avalanche usually results from a slope becoming unstable whereas a hot debris avalanche is the result of volcanic activity such as volcanic earthquakes or the injection of magma which causes slope instability. For several months before Mount St. Helens erupted in 1980, magma was injected into the north flank of the volcano creating a bulge that was extremely unstable.
Geological evidence shows that the larger a debris avalanche is, the faster it moves.
The reason for this is due to energy stored in material within the avalanche. Some large avalanches have been known to carry blocks as large as three kilometers in length, several kilometers from their source. Landslide is a general term for mass movement. It implies a gradual movement rather than the more sudden movement of an avalanche. The perfect example of possible large scale landsliding currently taking place is on the south side of the island of Hawai'i.