The Blackhawk Landslide Lucerne Valley, California By Matt O'Hare

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The Blackhawk LandslideLucerne Valley,
CaliforniaBy Matt O'Hare
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Geology of the Area

• Mountain is a resistant mass of marble thrust
  northward over uncemented sandstone and weathered
  gneiss.
• Top of mountin is 6800 ft high
• Extensive large scale faulting
• North side of mountain falls 3000 feet in a mile
• Uplift of Blackhawk mountain occurred in two
  stages
• Over thrusting from the south
• Monoclinal folding along a northwest trending
  axis

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Slide evidence

• Alluvial fan at foot of mountain is 100 ft thick,
  2 miles wide, and 5 miles long
• Striation evidence shows the landslide moved as
  almost a nondeforming mass of breccia at nearly
  100MPH
• At least 2 previous slides

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More slide facts

• Slide is 30 ft thick at terminus, 100 ft thick at
  base
• 10 billion cubic ft or 700 million tons of
  crushed marble
• One of largest ever in north america

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How did the slide move so far?

• Was not internally lubricated or slow moving like
  mudslides
• Water lubrication possible but would require
  massive rains
• Possibly air-lubrication method
• Compressed air allows for speed and distance as
  well as staying whole

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Air-lubrication method

• Slide launched off step about 200 feet high
• Trapped air and compressed it upon landing
• Sandstone and gneiss weathered away to leave
  precarious slope
• Would have supported speeds up to 270 MPH

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What can we learn from this?

• Landslides can move really fast
• Rockfall is extremely dangerous even if you are
  far away from it
• What can we do to prevent this?

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Citations

• Monastersky R. (1992) When Mountains Fall. Sci.
  News 142, 136-138.
• Rodrigue, Frank (2003) The Blackhawk
  Landslide.
• Shreve, Ronald (1959) Geology and
  Mechanics of the Blackhawk Landslide,
  Lucerne Valley, California. California Institute
  of Technology.