LANDSLIDES IN THE PACIFIC NORTHWEST

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LANDSLIDES IN THE PACIFIC NORTHWEST Recent
Advances and Ongoing Challenges
West of the Cascades
Contributors Rex Baum, Bill Burns, Derek
Cornforth, Tom DeRoo, Mike Dewey, Jason Hinkle,
Charlie Hammond, Oldrich Hungr, Dick Iverson,
Matthias Jakob, Ian Madin, Jon Major, John
Seward, Susan Shaw, Doug VanDine, Fred Swanson
Compiled by Tom Pierson, U.S. Geological Survey
Pe Ell landslide, Washington, 2007 USGS photo
archive
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Fundamental advances over last 15 20 years?

• In predicting the location and timing
  of landslides
• In understanding initiation mechanisms and
  mechanics of movement
• In mitigation of landslide hazards

Hwy 229, Oregon, 1998, USGS photo archive
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Advances In predicting the location and timing
of landslides --- New landslide imaging and
detection technologies

• LiDAR (Light Detection and Ranging) imagery for
  constructing bare earth DEMs
• InSAR (Interferometric Synthetic Aperture Radar)
  for detecting small vertical movements of ground
  surface over variable time intervals
• CRTDP (Close-Range Terrestrial Digital
  Photogrammetry) for mapping natural and
  engineered rock slopes
• TLS (Terrestrial Laser Scanning) for measuring
  the 3-dimensional coordinates of complex target
  surfaces using a ground-based instrument

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Advances In predicting the location and timing
of landslides --- New or improved models for
predicting slope instability and run-out areas

• SHALSTAB, a digital terrain model for mapping
  shallow landslide potential
• SINMAP, a stability index model for mapping
  terrain stability
• SCOOPS, a 3-D model that quantifies relative
  stability of all part of a digital landscape
• TRIGRS, a model to analyze time-dependent
  rainfall infiltration and slope stability
• LAHARZ, a semi-empirical method to delineate
  inundation limits and run-out distances

LAHARZ output used in hazard map
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Advances In predicting the location and timing
of landslides --- Improved mapping, analysis,
and monitoring capabilities

• GIS (Geographic Information Systems) new
  capabilities in layering, synthesizing,
  analyzing, presenting spatial data
• GPS (Global Positioning System) portable
  devices for accurate field locations and mapping
• Development of cheap automatic instrumentation
  for real-time monitoring and telemetry of ground
  movement, precipitation, and ground water
• Improvement and wider availability of
  quantitative precipitation forecasts
• Advancement in computer technology

High-precision GPS determining location on
surface of a landslide Photo T.
Pierson
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Advances In predicting the location and timing
of landslides --- Development of debris-flow
warning systems

• Based on precipitation monitoring and using
  empirical rainfall and antecedent moisture
  thresholds (Oregon and Seattle-area systems)
• Based on flow detection using acoustic flow
  monitors or AFMs (lahar warning system in
  Puyallup and Carbon River valleys at Mount
  Rainier)

Diagram of AFM station installed to detect ground
vibrations from passing debris flow
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Because lahars can occur without warning, a lahar
detection and warning system has been deployed on
the west side of Mount Rainier
- Seven detection sites on each river -two
repeaters -five AFM Sites
Tacoma
Fife
LESA
Puyallup
Sumner
Camp Murray
Orting
South Prairie
Wilkeson
Carbonado
Carbon River
Puyallup River
Yelm
Eatonville
Pierce County, Washington
Elbe
Ashford
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Advances In understanding initiation mechanisms
and mechanics of movement

• Experimental studies and modeling of field-scale
  debris flows at USGS Debris-Flow Flume near
  Eugene, Oregon
• One result recognition of effect of initial
  soil porosity (and subsequent contraction or
  dilation during failure) in determining whether
  slide mass will liquefy to form a debris flow
• Numerous long-term, real-time monitoring studies
  of landslides and other focused field studies
• One result recognition of effects of canopy
  removal in triggering debris flows in steep
  forested terrain

Experimental debris flow at USGS flume on 14 Jun
2007 Photo R. Iverson
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Advances In mitigation of hazards (in addition
to those already covered)

• Landslide inventory maps increased production,
  wider availability
• Oregon Senate Bill 12 a step toward putting
  hazard maps to work
• Some improved awareness of landslide hazards
  among agencies
• Interagency partnerships
• Improved mitigation engineering practices

Debris flow on Oregon highway, 2007 USGS photo
archive
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Outstanding problems and issues?

• Limited understanding of inherent complexity of
  natural slopes and precipitation variability
• Limited ability to accurately predict location
  and volume of landslides
• Inadequate coverage of landslide inventories
• Uncertain effects of climate change on landslide
  hazards
• Limited funding for landslide investigations
• Perceived disconnect between academic researchers
  and geotechnical practitioners
• Lack of regional systems for documenting
  landslide occurrence in real time
• Reluctance of regulatory agencies (in the face of
  development and property rights pressures) to
  fully utilize landslide studies and maps to
  regulate development

Debris-flow tracks, Oregon Coast Range USGS
photo archive
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Informing the emergency managers, land managers,
elected officials, and the public about landslide
hazards How are we doing?

• Difficult to assess
• Many emergency managers have a relatively good
  understanding of landslide hazards, especially if
  jurisdictions recently affected.
• Some elected officials, high-level agency
  managers, and residents in high-risk areas have
  only a minimal awareness or understanding of
  landslide hazards

School in potential lahar path, Orting,
Washington Photo D. Wieprecht
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Possible solutions for more effective mitigation

• More (and more effective) educational outreach,
  including more use of the media
• More interaction and information transfer between
  academic researchers and landslide practitioners
• More exposure of agency heads and elected
  officials to landslide issues
• More government support for application of
  landslide hazards maps

Magnolia area, Seattle, 1997 USGS photo archive
Most scientists (and engineers?) dont want to
bother with outreach . . .
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But its worth the effort.
Home at head of landslide, Stevenson, Washington,
2007, soon to be lost to retrogressing head scarp
Photo T. Pierson