Anatomy of a landslide

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Anatomy of a landslide
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Erosional Phases

• No erosion
• Rapid Erosion
• Slow Erosion

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No erosion

• Can last seconds to decades
• Volume of deposit increases as upstream sediments
  are trapped
• Debris dams are more likely to form and persist
  with large amounts of woody debris

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Rapid erosion

• Incision through sediment occurs during the
  development of new channels
• Downcutting may be limited by bedrock or coarse
  armoring material supplied by landslide
• Rough estimate of material moved during this
  phase length of channel affected x channel
  width x depth of deposit
• Phase ends when channel geometry is equilibrated
  to upstream water and sediment discharge

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Slow erosion

• Sediment is supplied primarily by bank erosion
• Supply rate is a function of flood occurrence,
  channel shifting and the establishment of bank
  vegetation

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Significance of landslides

• Sediment input affects riparian habitat
• Infilling of Salmon redds
• Gravel recruitment
• Societal impacts
• Damage to infrastructure
• Potentially lethal

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The 1983 Thistle landslide at Thistle, Utah-This
landslide began moving in the spring of 1983 in
response to groundwater buildup from heavy rains
the previous September and the melting of deep
snowpack for the winter of 1982-83. Within a few
weeks the landslide dammed the Spanish Fork
River, obliterating U.S. Highway 6 and the main
line of the Denver and Rio Grande Western
Railroad. The town of Thistle was inundated under
the floodwaters rising behind the landslide dam.
Total costs (direct and indirect) incurred by
this landslide exceeded 400 million, the most
costly single landslide event in U.S. history.