Topic 8: Landslides and Permafrost

definition of landslide

the movement of a mass of rock, debris, or earth down a slope, OR: mass movement, slope failure

weathering

set of chemical and physical processes that alter states of rock and mineral at/near Earth's surface

two types of weathering

physical/mechanical and chemical

physical/mechanical weathering

breaking up of rocks and minerals by physical processes i.e. disintegration, caused by freezing/thawing, tractive forces, comminution and abrasion in streams

chemical weathering

changing from one chemical state to another i.e. decomposition

erosion

transport or movement of material at surface

debris

weathered material transported by landslide

driving forces/shear force

forces parallel to slope that cause landslides: gravity, moisture/ppt, pore water pressure, slope, erosion, loading weight, tectonics

resisting forces/shear strength

forces normal to slope that work to prevent landslides: sediment/rock cohesive strength, vegetation, structure

Fp (driving force) \> Fn (resisting force) =

slope failure

shear strength \> shear force =

stable slope

system of landslide classification

Cruden and Varnes, based on type of material and movement

bedrock definition

cohesive material

falls

rapid, free-falling, rolling, bouncing, measured in metres/min to m/s

topples

rapid rotation of a mass about a point

slides

movement along one or more distinct surfaces

rotational slides

slumps, curved failure plane

translational slides

planar failure plane

lateral spreads

lateral movement of ground, usually accompanied by subsidence

flows

viscous fluid movement, ranges from slow to fast

complex classification

2+ types: falls, topples, slides, spreads, flows

hazard definition

process, phenomenon, or human activity that may cause loss of life, injury, or other health impacts

risk definition

probability that a community/property/area will be damaged or disrupted by a particular hazard

vulnerability definition

degree of loss to a given element/set of elements resulting from a hazard, characteristics/circumstances that make a community/system/asset susceptible to damage

exposure

at-risk property or population

resistance

measures taken to prevent, avoid, or reduce loss

resilience

ability to recover prior state or achieve desired post-disaster state

permafrost

thermal condition predicted from air temp, frozen ground

active layer detachment slides

shallow permafrost landslides, some transition to deeper

thaw slumps

retrogressive thaw flow slides

deep-seated permafrost landslides

base of permafrost failure, large-scale, thaw induced, only 4 since the first in 2016

consequences of Frank Slide

30 million m3 of rock buried a portion of the town and killed more than 70 people

causes of Frank Slide

unstable geological structure of Turtle Mountain and mining

example of man-made landslide

Vaiont (Italy), caused by creation of a dam