Post on 21-Jan-2016
description
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LANDSLIDES VS. MUDFLOWS
MUDFLOWMUDFLOW
LANDSLIDELANDSLIDE
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What is a Landslide?What is a Landslide?
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SlideSlide
Venuzuala, Coast RoadVenuzuala, Coast Road
UVM GeohazardsUVM Geohazards 44Three major controls...Three major controls...
Where do Landslides Occur?
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WHAT CAUSES LANDSLIDES?
STEEP SLOPES AND WATER.
WHY?
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Why do landslides
occur?
Strength of Strength of rock/soil rock/soil exceededexceeded DRIVING forceDRIVING force
RESISTING forceRESISTING forceDRIVING forceDRIVING force
RESISTING forceRESISTING force
>>>>
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FORCE BALANCE
GRAVITY
FRICTION AND
COHESION
DRIVING VERSUS RESISTING
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Simple Physics……vectors DRIVING force is gravity, DRIVING force is gravity, RESISTING force is soil/rock strength/frictionRESISTING force is soil/rock strength/friction Steep slopes give greater Driving ForceSteep slopes give greater Driving Force
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WHY STEEPWHY STEEP SLOPES ?SLOPES ?
STEEP SLOPES INCREASE STEEP SLOPES INCREASE DRIVING FORCE, DRIVING FORCE,
DECREASE STRENGTHDECREASE STRENGTH
Yungay, Peru
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GRAVITY
FRICTION AND
COHESION
NORMAL FORCE
GREATER THE NORMAL FORCE THE GREATER THE RESISTING FORCE
What is normal anyhow?
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What does slope have to do with normal forces?????
LENGTH OF VECTOR = MAGNITUDE
Can demo dry
TAKE HOME MESSAGE: Steep slopes reduce normal force and thus resistance to sliding
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WHY WATER ?WHY WATER ?
WATER DECREASES WATER DECREASES STRENGTH BY LOWERING STRENGTH BY LOWERING
NORMAL FORCE -- NORMAL FORCE -- “FLOATING”“FLOATING”
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SUBTRACTING VECTORS
FORCE BALANCE TIPS
WET
NORMAL FORCEBOUYANCY FORCE
IF DRY
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WHAT CAUSES MUDFLOWS?
WATER, LOOSE SEDIMENT, STEEP SLOPES
San Rafael,CA
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HOW DO MUDFLOWS WORK?
Intimate mixture of sediment and waterIntimate mixture of sediment and water OFTEN start from landslidesOFTEN start from landslides One phase flowOne phase flow Move under gravity forceMove under gravity force Have a yield strength -- plastic behaviorHave a yield strength -- plastic behavior Stop when they get too thin or slope Stop when they get too thin or slope
lessens -- DRIVING vs. RESISTING lessens -- DRIVING vs. RESISTING FORCESFORCES
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Three phases of a mud/debris flow..
Bouldery snout
Mud and rock middle
Watery tail
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MUD AND DEBRIS FLOWS LEAVE DIAGNOSTIC CLUES Bouldery snouts -- frozen on low slopeBouldery snouts -- frozen on low slope Marginal levees -- too thin to keep Marginal levees -- too thin to keep
flowing, boulderyflowing, bouldery Unsorted sediments -- not enough water Unsorted sediments -- not enough water
to sort materialto sort material
snout
levee
levee
v
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Bouldery Snouts
Sierra Nevada, Lone Pine, Owens Valley
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Marginal levees
Sierra Nevada, Lone Pine, Owens Valley
RV for scale
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Unsorted sediments
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WHERE ARE MUDFLOWS MOST LIKELY TO STRIKE?
ANY WHERE WITH STEEP SLOPES, VERY HEAVY RAIN,
AND LOOSE SEDIMENT...
THIS INCLUDES DESERTS, THE ARCTIC, AND THE TROPICS.
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DESERT EXAMPLE, SIERRA NEVADA, CALIFORNIA
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ARCTIC EXAMPLE. CANADA
MELVILLE ISALND
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WHAT SETTINGS EXACERBATE
MUDFLOW HAZARDS?
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Valleys NEAR VOLCANOES are risky places to be
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WHAT ARE MUDFLOW DANGERS?
Erosion then deposition
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INFRASTRUCTURE DISRUPTION
VERDUGO HILLS CEMETARY,
Glendale California
Apartments, Venezuela
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BURIAL
LOS ANGELES
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Debris Delivery
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USGS Debris Flow Video