How does a flow-type landslide behave like a viscous fluid?

A flow-type landslide is characterized by a distribution of particle velocities that resembles the movement of a viscous fluid. This behavior occurs when the mass of rock, debris, or earth becomes fluidized, most commonly by the introduction of water, though trapped air can also act as a fluidizing agent.1

In these events, the internal movement of the material is not restricted to discrete shearing surfaces, as seen in slides; instead, the mass moves in a way that mimics fluid dynamics. The contact between the moving mass and the underlying surface may be distinct or characterized by diffuse shear. The degree of this fluid-like behavior is often gradational, depending on factors such as the material's fluid content and mobility. For example, a mudflow exhibits high viscosity due to its high concentration of suspended particles and silt, which limits how far it can travel compared to a standard water flow.12