What is a flow phenomenon?
(Extract from Maquaire and Malet, 2006)
A flow is a landslide in which the individual particles travel separately within a moving mass. Unlike slides, occurring along more or less well-defined shear zones, flow-like landslides are characterised by internal differential movements that are distributed throughout the mass (Picarelli, 2001). Their flow-like morphologies are much longer than they are wide and their uneven topography shows successive lobes. They have a considerable erosive capacity and can carry material eroded from slopes or banks over considerable distances and cover sizeable surfaces with varying thicknesses. They contribute to positive erosion balances, as the material can be carried outside the slope basin. Coussot (1993) suggests a rheological classification of these flows. Hungr et al. (2001) distinguish several types of shallow flow-like landslides.
Debris flow and debris avalanche:
Debris flow is a very rapid to extremely rapid flow (> 1 m.s-1) of saturated non-plastic debris in a steep channel. The key characteristic of a debris flow is the presence of an established channel or regular confined path, unlike debris avalanches which are thin, partly or totally saturated, and which occur on hillslopes. Debris flows and debris avalanches are complex movements. They consist of a mixture of coarse material (gravel and boulders) embedded in a sandy-silty matrix, with a variable quantity of water (Costa and Wieczorek, 1987; Iverson et al., 1997). In spite of varying velocities and total solid fractions debris flows and debris avalanches show many similarities, particularly in the way they are triggered. Debris flows and debris avalanches are commonly triggered by an excess of water: intense rainfall, rapid snowmelt, and more rarely, glacier or lake overflows which mobilize unconsolidated material in their path. Rainfall intensity and duration, along with antecedent rainfall conditions, are strong controls for debris flow triggering (Dikau et al., 1996).
Mudflow (soil flow)
Mudflows (or Soil flows) are similar in form and behaviour to debris flows. They can be very slow to very mobile and can flow downslope quite quickly. They tend to follow gullies or shallow depressions to spread out into a flat, bulbous fan or even a thin sheet.
References:
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