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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

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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