Mountain Landforms and Geomorphic Processes - Mountain Geography: Physical and Human Dimensions - page 255

ing observed the actual event, it is often difficult to distinguish between different types
of flow. However, common to all flows are high moisture content and rapid movement.
The conditions most favorable for mudflows include (1) abundant water to saturate
the mass of mud and rocks, (2) a lack of stabilizing vegetation, (3) unconsolidated ma-
terial with adequate fines to act as a lubricant, and (4) moderately steep slopes (Harris
et al. 2001). They occur most often in spring and summer, when there is ample snowmelt
and heavy rain during thunderstorms. Under these conditions, masses of unconsolid-
ated material may become saturated, and the material may collapse and flow downslope
where an unstable situation already exists.
The typical point of origin for a mudflow is at a high elevation on the slope where
there is a source of moisture, such as a confluence of runoff or below snow patches.
Mudflows also occur where gradient increases abruptly at a break in the slope. In the
Ruby Mountains, Yukon Territory, solifluction lobes on gentle slopes above a glacial
trough slowly migrate onto the steeper slope. Eventually, they become unable to main-
tain themselves and collapse, moving downslope as mudflows (Price 1969). Whatever
the local situation, once a mudflow channel has been established, it is likely that future
flows will follow the same path.