Environmental Engineering Reference
In-Depth Information
Weathered
bedrock,
soil,etc.
After Heim (1932)
Elm, Switzerland 1881
Very rapid to
extremely rapid
(a)
(b)
Dry sand
Firm silt
sand
Very rapid
(c)
(d)
Terraced fields
lake
Loess
Glacial clay
and silt
Riviere blanche,
quebec
0 1000ft
After sharpe
(e)
(f)
Very rapid
About 9 km
FIGURE 9.4
Avalanches and flows in rock, debris, and soil. (a) Rock fragment flow or rockfall avalanche. (This type of
movement occurs only when large rockfalls and rockslides attain unusual velocity. Extremely rapid [more than
130 ft/sec at Elm, Switzerland.) (b) Debris avalanche. (c) Debris flow. (d) Sand run: rapid to very rapid. (e) Dry
loess flow caused by earthquake (Kansu Province, China, 1920). Extremely rapid movement. (f) Soil or mud
flow. (g) Achacolla mud flow (La Paz, Bolivia). Huge mass of lacustrine soils slipped off the altiplano and
flowed downstream for 25 km (see
Figure 9.57)
.
(Parts a-f from Varnes, D.J.,
Landslides and Engineering Practice
,
Eckel, E.B., Ed., Highway Research Board, Washington, DC, 1958. Reprinted with permission of the
Transportation Research Board.)
Magnitude
refers to the volume of material which may fail, the velocity of move-
ment during failure, and the land area which may be affected. It depends very
much on the form of failure as related to geology, topography, and weather con-
ditions.
●
Probability
is related in a general manner to weather, seismic activity, changes in
slope inclinations, and other transient factors.
●
