# Theory

In the extended model the flowing avalanche core ($\Phi$) consists of clumps and clods of snow (granules); the cloud consists of mixture of air and ice-dust ($\Pi$), see Fig. 1. The core is physically treated as a gravitationally driven, granular shear flow; the cloud is modelled as an inertial, turbulent suspension. Because the snow material in the core is non-suspendable and the ice-dust in the cloud is suspendable, two flow layers exist simultaneously, but with different flow densities ($\rho_{\Phi}$, $\rho_{\Pi}$) and speeds ($\textbf{u}_{\Phi}$, $\textbf{u}_{\Pi}$). The layers are formed by natural segregation because of the large difference in particle sizes – dust (< 1mm) and granules (>1cm) – and therefore settlement speeds.

#### Random Kinetic Energy

The Random Kinetic Energy (RKE) approach splits the shear work rate into the production of thermal and granular temperatures.

#### Entrainment

Avalanche interaction with the snowcover is physically treated as an elastic-plastic collision in which snow can be entrained (plastic collision).

#### Temperature

It has long been recognized that warm, moist snow behaves differently than cold, dry snow.

#### The Formation of the Powder Cloud

The avalanche cloud is mathematically treated as an inertial, turbulent suspension.

#### Forest

The forest module applies the detrainment method developed by Feistl et al. 20??.

#### Pressure Modules

The RAMMS::Extended model contains two pressure modules.