Denudation, weathering and mass wasting - Fundamentals of the Physical Environment - page 399

it to appear, or daylight , in the rock wall. Single fractures provide translation or release
surfaces in planar slides (Plate 13.8a) but most rock walls fail by wedge slides (Plate
13.8b), where the release surface is the intersecting plane ( I ) between two fractures.
Toppling failure occurs where

Figure 13.12 Rates and types of slope failure.
Table 13.2 Classification of mass wasting by materials, rates and
processes

Mode of
failure

Rate of
movement

Water
content

Type of material

Snow/ice Rock Rock

debris

Colluvium Soil

Flow Very fast Very

high

Slush
avalanche

Debris flow

Lahar (+ volcanic

debris)

Very fast Low Snow

avalanche

Rock
avalanche

Debris
avalanche

Moderate-
fast

High Mudflow

Moderate Moderate Sand run

Very slow Very

high
(Frozen)

Rock
glacier

Fall Fast Low Rock fall Cohesive block

fall

Individual block/grain
fall/topple

Fast Low Topple Cohesive topple