lecture 12 Flashcards
landslides
mass movements occur when large volumes of material move downslope under the influence of gravity, when material is rock soil mud or debris
how can slope instability be increased
increasing slope angle
adding to the mass of material (water)
shaking the slope (earthquake)
reducing friction (water)
components of gravity acting on slope
- component parallel to slope
2. component perpindicular to slope
role of water
if air in pore space is replaced by water, weight increases dramatically
water is incompressible so if rock is buried by more sediments the pore pressure increases and strength is reduced
water expands when it freezes so it forces cracks apart (frost shattering)
groundwater can dissolve minerals that bind rock together and form caves
role of geology
calcium carbonate and evaporitic rocks are dissolvable and can form sinkholes
clay minerals are platy sheet silicate minerals that expand when wet, allowing them to slide past eachother
sedimentary rock contains bedding lanes which sliding occurs, may be stable or unstable
till
clay rich glacial deposits
- clays are byproduct of grinding aciton of ice on bedrock
landslide in china
material sliding downslope along a bedding plane
the role of tectonics
tectonics generates topography and steepens slope, and shaking in large earthquakes dislodges material from hillslopes
preconditions
bring a slope to brink of failure
ex. tectonics
triggers
push it over the edge
ex. shaking
2018 mW 7.5 Palu
preconditions of earthquake induced lateral spread
how does death toll compare with earthquake and volcanic eruptions total death toll and number of deadly events
- earthquakes are more deadly than landslides which are more deadly than volcanic eruptions
- deadly landslides are more frequent than deadly earthquakes
when did the last major hazard occur in Canada
1970
