Usually a landslide moves a limited distance. Some landslides move much further.
Features of long run-out landslide:
(1) The material runs out a great distance after it reaches its horizontal base.
(2) The material moves very fast.
(3) The material behaves as a frictionless material.
(4) The movement does not have the features of a lahar, with a low water content.
In a normal landslide the maximum horizontal distance traveled is less than or equal to the maximum vertical distance of fallen material. With a long run-out landslide the material runs many times this distance and can even run uphill.
Theories for the frictionless behavior:
(1) layer of trapped air
(2) layer of trapped water, possibly pressed from the ground by pressure
(3) vibration
(4) small rocks at the bottom acting as ball bearings.
These landslides are difficult to outrun and can bury houses considered safe from avalanche.
