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How does a spread form during a landslide?
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landslide
This 1995 landslide at La Conchita, a coastal town in California, swept away a hillside road and destroyed a number of houses.
A spread is a specific type of landslide characterized by the complex lateral movement of relatively coherent earth materials. It forms when these coherent blocks rest upon a weaker substrate that is susceptible to soil liquefaction or plastic flow.1
The process typically unfolds as follows:
- Substrate Failure: The underlying weaker materialāsuch as loess or other weakly cemented siltsāundergoes liquefaction or plastic flow, often triggered by earthquake shock or water saturation.1
- Subsidence: As the substrate loses its strength, the coherent blocks of material above it subside into the weaker layer.1
- Lateral Movement: This instability leads to a slow, downslope lateral movement. This process can extend over long distances due to retrogressive extension, often originating from features like eroding riverbanks or coastlines.1
In essence, the movement is driven by the failure of the underlying support, causing the overlying mass to spread and break apart as it shifts laterally.1