Geoscience Reference
In-Depth Information
tended to bring in different terminology that at times is
confusing and contradictory.
A useful classification in terms of material and
movement is shown in Table 12.1. This classification
has since been modified to include topples and lateral
spreads. The scheme emphasizes the composition of
the material being moved, but it and its modification
clearly do not include time. From the hazard point
of view - in terms of warning, human response, and
prevention - these classifications can be limited. A
temporal classification that gives some concept of the
speed of movement of instability can be more attrac-
tive. In Table 1.4, which ranks hazard characteristics
and impacts mentioned in this text, some emphasis is
placed on the suddenness of the event. One such
temporal classification is shown in Figure 12.6. It is
immediately obvious that this classification includes
expansive soils, which are ignored in most engineer-
ing and morphometric classifications. Figure 12.6
is used in this chapter, not because it is better than
United States Highway Research Board Landslide Committee classification of mass movements (from Leopold et al., 1964).
Table 12.1
Type of
material
Bedrock
Soil
Type of
movement
Falls
Rockfall
Soil fall
Rotational
Planar
Rotational
No. of Units
Few
Slump
Block glide
Block slump
Slides
Many
Rockslide
Debris slide
Lateral spread
All unconsolidated
Rock
fragments
Sand
or silt
Mixed
Plastic
Moisture content
Dry
Rock
fragment
flow
Sand
run
Loess
flow
Flows
Slow
earth
flow
Creep
Rapid
earth
flow
Debris
avalanche
Solifluction
Mud flow
Debris flow:
sand or silt
Rubble flow:
dirty snow
avalanche
Wet
Velocity (cm s
-1
)
10
-9
10
-8
10
-7
10
-6
10
-5
10
-4
10
-3
10
-2
10
-1
10
0
10
1
10
2
10
3
10
4
1 mm yr
-1
1 cm yr
-1
1 mm day
-1
1 cm day
-1
1 cm hr
-1
1 km yr
-1
1 cm min
-1
1 km hr
-1
1 m s
-1
100 m s
-1
rockfalls
creep
mud & debris flows
solifluction
debris avalanches
expansive soils
landslides & slumps
air supported flows
Classification of land instability based upon rate of movement (derived from Finlayson & Statham, 1980).
Fig. 12.6
