Models

Many mechanical models have been proposed for debris avalanches, some of which are introduced and categorized by Shaller and Smith-Shaller （1996）.

 Shaller and Smith-Shaller grouped these models attempting to explain the universal characteristics into three categories;

1. Bulk Fluidization Model
2. Basal Lubrication Model
3. Mass Loss Model

Bulk Fluidization Model

Models categorized under the bulk fluidization model assumes the that clasts forming the debris avalanches move similar to how molecules move in a fluid, and therefore give debris avalanches the appearance of a flowing body.

Hsü (1975) suggested a flow mechanism based on grain flow proposed by Bagnold (1954). 

Grain flow is a flow whose whole movement is dominated not by the flow of interstitial fluid but by the collision of cohesionless particles that aggregate and are suspended neutrally in the fluid. Hsü proposed that the dense dusts of crushed rocks act as the interstitial fluid, and that these are the debris-avalanche matrix.

Davies (1982) suggested that debris avalanche is fluidized by high basal  shear rates (mechanical fluidization), also based on the grain flow model proposed by Bagnold (1954). Mechanical fluidization occurs when there is  high energy input to a granular material, which increases contact pressures between individual grains so that they become statistically separated and results in mass dilatation. Davies additionally stated that the volume effect was caused by spreading of a fluidized debris avalanche when it is deposited.

Melosh's (1979) proposed in his acoustic fluidization model that the sound field in the debris decrease friction by collision between clasts.

Basal Lubrication Model

The second category is the basal lubrication model. To explain the small apparent friction coefficient, these models suggest that a source of  lubrication exists under blocks.

Shreve (1968a,b) proposed the air-layer lubrication (air cushion) model. When a collapsing block sliding at high speed above the ground trips and jumps on protrusions or irregularities of the ground, it is supported by the air trapped in the basal layer and proceeds to slide without any effect of contact friction from the ground.  

Mass Loss Model

Models categorized under the mass loss model propose that the low apparent friction coefficient occurs because debris avalanche drop off low-velocity mass as a multi-stage rocket. The model proposed by Van Gassen and Cruden (1989) is categorized under this group. The models in this group differ from the previous two groups because they assume that debris are deposited during the run.

Other models have also been proposed such as the Bingham flow model (Voight et al., 1983; etc.) in which a debris avalanche behaves like a Bingham fluid (a  rigid plug-like body rides on a laminar boundary layer that behave like a fluid due to strong shear stress), and the basal guided wave model (Kobayashi, 1994) in which the dynamic mechanism resulting from the existence of a granular material layer causes the lowering of the friction coefficient.