|
Landslide Type
|
Type of Material
|
Slope Angle
|
Remarks
|
| Rock
falls |
Rocks
weakly cemented, intensely fractured, or weathered; contain conspicuous
planes of weakness dipping out of slope or contain boulders in a weak matrix. |
40º
1.7:1
|
Particularly
common near ridge crests and on spurs, ledges, artificially cut slopes,
and slopes undercut by active erosion. |
| Rock
slides |
Rocks
weakly cemented, intensely fractured, or weathered; contain conspicuous
planes of weakness dipping out of slope or contain boulders in a weak matrix. |
35º
1.4:1
|
Particularly
common in hillside flutes and channels, on artificially cut slopes, and
on slopes undercut by active erosion. Occasionally reactivate preexisting
rock slide deposits. |
| Rock
avalanches |
Rocks
intensely fractured and exhibiting one of the following properties: significant
weathering, planes of weakness dipping out of slope, weak cementation,
or evidence of previous landsliding. |
25º; 2.1:1
|
Usually
restricted to slopes of greater than 500 feet (150 m) relief that have
been undercut by erosion. May be accompanied by a blast of air that can
knock down trees and structures beyond the limits of the deposited debris. |
| Rock
slumps |
Intensely
fractured rocks, preexisting rock slump deposits, shale, and other rocks
containing layers of weakly cemented or intensely weathered material. |
15º
3.7:1
|
|
| Rock
block slides |
Rocks
having conspicuous bedding planes or similar planes of weakness dipping
out of slopes. |
15º; 3.7:1
|
|
| Soil
falls |
Granular
soils that are slightly cemented or contain clay binder. |
40º
1.7:1
|
Particularly
common on stream-banks, terrace faces, coastal bluffs, and artificially
cut slopes. |
| Disrupted
soil slides |
Loose,
unsaturated sands. |
15º
3.7:1
|
|
| Soil
avalanches |
Loose,
unsaturated sands. |
25º
2.1:1
|
Occasionally
reactivate preexisting soil avalanche deposits. |
| Soil
slumps
(Anaheim
Hills soils types) |
Loose,
partly to completely saturated sand or silt; uncompacted or poorly compacted
manmade fill composed of sand, silt, or clay, preexisting soil slump deposits. |
10º
5.7:1
(A
slope angle greater than this is unacceptably
dangerous.)
|
Particularly
common on embankments built on soft, saturated foundation materials, in
hillside cut-and-fill areas.
(These
dangerous conditions are present in Anaheim Hills.) |
| Soil
block slides
(Anaheim
Hills soils types) |
Loose,
partly or completely saturated sand or silt; uncompacted or slightly compacted
manmade fill composed of sand or silt, bluffs containing horizontal or
subhorizontal layers of loose, saturated sand or silt. |
5º
11:1
(A
slope angle greater than this is unacceptably
dangerous.)
|
Particularly
common in areas of preexisting landslides along river and coastal flood
plains, and on embankments built of soft, saturated foundation materials.
(These
dangerous conditions are present in Anaheim Hills.) |
| Slow
earth flows |
Stiff,
partly to completely saturated clay and preexisting earth-flow deposits. |
10º
5.7:1
|
|
| Soil
lateral spreads |
Loose,
partly or completely saturated silt or sand, uncompacted or slightly compacted
manmade fill composed of sand. |
0.3º
190:1
|
Particularly
common on river and coastal flood plains, embankments built on soft, saturated
foundation materials, delta margins, sand dunes, sand spits, alluvial fans,
lake shores and beaches. |
| Rapid
soil flow |
Saturated,
uncompacted or slightly compacted manmade fill composed of sand or sandy
silt (including hydraulic fill earth dams and tailings dams); loose, saturated
granular soils. |
2.3º
25:1
|
Includes
debris flows that typically originate in hollows at heads of streams and
adjacent hillsides; typically travel at tens of miles per hour or more
and may cause damage miles from the source area. |
| Subaqueous
landslides |
Loose,
saturated granular soils. |
0.5º
110:1
|
Particularly
common on delta margins. |
