landslides Earth Science

Creep on a frozen slope is a slow account kept by gravity and frost together. In the warm season the active layer thaws downward while the ground beneath stays frozen and impermeable, so meltwater cannot drain; the surface turns to soft mud whose shear strength collapses, and the layer flows downhill along that frozen interface. Winter ice crystals lift the particles and thaw drops them straight back down, each cycle nudging the displacement a little further downslope. It moves only millimeters to centimeters a year, the opposite of a landslide, which has a slip surface and fails at an instant; its tells are drunken forests of tilted trunks and roots bent into bows. Let the active layer get too wet and creep escalates into a real slide.

A landslide is rock and soil sliding downslope on a slip surface, often after rain or quakes.

A debris flow is a fast river of mud, rock and water set loose by heavy rain or melt, rushing down valleys with great force.