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Earthflow Recognition Features: Topographic Expression and Diagnostic Patterns

Explore the topographic features and patterns that can help identify and recognize earthflows, the most common form of landslippage. Learn how to interpret drainage and topographic keys, identify diagnostic patterns, and understand the age and complexity of earthflow formations.

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Earthflow Recognition Features: Topographic Expression and Diagnostic Patterns

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  1. Part 9 RECOGNITIONFEATURES ofEARTHFLOWS

  2. Topographic Expression of Earthflows

  3. 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”

  4. Diagnostic 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

  5. Topographic Keys to Identify Earthflows • Opposing contours • Headscarp evacuation areas • Necking down at transition between deflation/ inflation zones

  6. 10 to 100 years old 100 to 500 years old Earthflow features become increasingly mollified with the passage of time, making them difficult to discern More than 500 years old

  7. Earthflows tend to form coalescing complexes, with one or two lobes active at any given time, separated by long periods of dormancy

  8. As earthflows become less frequent their areal limits become increasingly sketchy

  9. PROFILES of COALESCING EARTHFLOWS Each successive earthflow tends to truncate and mask the previous event

  10. Examples of earthflows in the Appalachian Highlands mapped by the USGS

  11. Crowley’s Ridge Earthflows

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