Post on 21-Dec-2015
Earthflows are statistically the most common form of landslippage
They tend to form in the axes of colluvial-filled ravines or areas of thick residual soils
One flow tends to pile upon upon another, building large “debris fans”
Diagnostic Topographic PatternsDiagnostic Topographic Patterns• Use drainage and
topographic keys to recognize anomalous site characteristics typical of landslides• Divergent contours• Crenulated
contours• Arcuate headscarp
evacuation areas• Isolated
topographic benches
Topographic Keys to Identify Topographic Keys to Identify EarthflowsEarthflows
• Opposing contours
• Headscarp evacuation
areas• Necking
down at transition between deflation/inflation zones
Earthflow features become increasingly mollified with the passage of time, making them difficult to discern
10 to 100 years old 100 to 500 years old
More than 500 years old
Earthflows tend to form coalescing complexes, with one or two lobes active at any given time, separated by long periods of dormancy
• As earthflows become less frequent their areal As earthflows become less frequent their areal limits become increasingly sketchylimits become increasingly sketchy
PROFILES of COALESCING PROFILES of COALESCING EARTHFLOWSEARTHFLOWS
Each successive earthflow tends to truncate and mask the previous event