Los Angeles:
Introduction
Reading
Focus Question
The Interested Parties
The Los Angeles Area - What You Need to Know
Climate - Warm, Dry Summers and Cool, Wet Winters
The Geologic Hazards of La Crescenta
Debris Basins - Catch It If We Can
NEWSFLASH!
For Your Information: We Have a Plan
Glossary
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Glossary: |
Use these definitions of important terms as you answer the Focus Question.
| clinometer |
An instrument used to measure angles. |
| debris flow |
A moving mass of water-saturated near-surface materials. |
| earthflow |
A flowing mass of fine-grained soil particles mixed with water. |
| sediment |
Solid rock or mineral fragments transported and deposited by wind, water, gravity, or ice. Sediment accumulates loosely in layers. |
| erosion |
The removal of weathered rocks by the action of water, wind, ice, or gravity. |
| Geologic environment likely to produce earthquake-induced landslides in the Los Angeles region. |
| Landslide Type |
Type of Material |
Minimum Slope Inclination |
Remarks |
| Rock falls |
Rocks weakly cemented, intensely fractured or weakened |
40 |
Common near ridge crests and on spurs, ledges, artificially cut slopes, and slopes undercut by active erosion |
| Rock avalanches |
Rocks intensely fractured and exhibiting significant weathering, planes of weakness dipping out of slope, weak cementation, or evidence of previous landsliding |
25 |
Restricted to slopes of > 153 yards relief that are undercut by active erosion |
| Rock slumps |
Intensely fractured rocks, preexisting rock slump deposits, shale and other rocks containing layers of weakly cemented or intensely weathered material |
15 |
|
| Disrupted soil slides |
Loose, unsaturated sands |
15 |
|
| Soil slumps |
Loose, partly to completely saturated sand or silt; poorly compacted manmade fill composed of sand, silt, or clay; preexisting soil slump deposits |
10 |
Common on embankments built on soft, saturated foundation materials, in hillside cut-and-fill areas, and on river and coastal flood plains |
| Soil block slides |
Loose, partly to completely saturated sand or silt; poorly compacted manmade fill composed of sand or silt |
5 |
Common in areas of preexisting landslides along river and coastal flood plains, and on embankments built on soft, saturated foundation materials |
| Soil earth flows |
Stiff, partly to completely saturated clay and preexisting earth-flow deposits |
10 |
|
| Soil lateral spreads |
Loose, partly or completely saturated silt or sand; slightly compacted manmade fill composed of sand |
0.3 |
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 flows |
Saturated, slightly compacted manmade fill composed of sand or sandy silt; loose, saturated granular soil |
2.3 |
|
| Subaqueous landslides |
Loose, saturated granular soils |
0.5 |
Common on delta margins (subaqueous part) |
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Click above thumbnails to view the full image.
Topograhic map (Activity 3). Study this topographic map of the La Crescenta area. Find the schools mentioned in the focus question, the debris basin, and the foothills of the San Gabriel Mountains. Note every feature, natural of manmade, that would affect children's safety in the event on the occurence of a geologic or hydrologic hazard. |
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U.S. Department of the Interior |
U.S. Geological Survey