Mass wasting and groundwater

mass wasting

downslope movement of earth’s materials due to gravity

when does mass wasting occur (physics)

when sheer stress (driving force) > sheer strength (resistance)

critical slope angle (depends on. 2 main factors)

the slope angle at which mass wasting occurs. depends on

1) strength of slope

2) water content

soil creep (mass wasting type)

most common. very slow (~1cm/yr) and gradual downslope movement. low H20 content.

solifluction creep (mass wasting type)

occurs in permafrost regions. H20 cant penetrate permafrost→ flows on top

slump (mass wasting type)

fast down slide along a curved surface

slide (mass wasting type)

moderate to fast failure of material along a planar surface

avalanches (mass wasting type)

VERY fast. can be rock, snow or debris. move fluidly similar to pyroclastic flow. can travel very far horizontally.

flows (mass wasting type)

Very fast and wet. can be mud, earth or debris. often moves like a viscous fluid.

groundwater (what/where is it?)

our main source of freshwater on earth. lives in pore spaces and fractures under earth’s surface. mostly in zone of saturation

zone of saturation

area below the water table where all porous spaces are filled with groundwater

unsaturated zone

area above the water table where some porous spaces are filled with water and some are filled with air

porosity

ratio of open spaces to solid material. expressed as a % of total volume of material

permeability:

how much porous spaces connect allowing water to flow through a material

unconfined aquifer

no confining layer between aquifer and earths surface

confined/artesian aquifer

has confining layer between aquifer and earth’s surface (aquitard). can lead to developing higher pressure.

aquitard

impermeable confining layer that hinders water movement (eg clay)

artesian well

if confined aquifer develops enough pressure water can flow on its own out of the well (no pumping needed)

piezometer

well drilled just to determine aquifer pressure. helps us to draw water table

hydraulic gradient

inclined surface in water table. can be calulated with rise over run

cone of depression

when water is pumped from a well faster than it can replenish surrounding aquifer level drops