Chapter 16 LANDSLIDES AND OTHER MASS MOVEMENTS SLUMP San Mateo County CA 1997 Velocity A few meters per day DEBRIS FLOW Sierra Nevada Stanislaus River Velocity A few meters per second LANDSLIDE La Conchita California Velocity About ten meters per second FAILURE SURFACES Weak layers below the surface that can nucleate motion Examples include weak sedimentary bedding e g shale layers and metamorphic foliation LA CONCHITA A mud ow had occurred here in 1995 due to heavy rains Note clouds of dust material is dry not wet The failure plane was a saturated layer deep within the 1995 deposit LA MONTAGNA CHE CHAMMINA Vaoint Dam rockslide Italian Alps 1963 Engineers built a dam heard rumbling then drained reservoir Dipping weak shale layers paralleled the slope 600 million tons of rock detached and slid downslope SNOW AVALANCHES Weak layer collapses leading to mass movement Analogous to landslides in this way WHY MASS MOVEMENTS OCCUR The force pulling mass downslope is greater than the force holding it in place Force holding mass in place is the resistance force friction Force pulling mass down is the downslope force gravity THREE FAILURE TRIGGERS Shocks and vibrations Changes in slope characteristics e g steepness Changes in slope strength e g weathering addition of water
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