L2, Mass Wasting Flashcards
produce soil
Continuous insidious retreat in humid/vegetated areas
Weathering by Biota
if no sediment and water → soil
sediment interactions with vegetation, animals and microbes, will tell you this is a terrestial environment
soil layer
process operates from top down
bare top soil easily removed (ex. dust bowl)
zone of leaching and zone of accumilation
topsoil: where vegetation grows
subsoil , bare rock
vegetation cover stabilises the surface but -
humus increases acidity of percolating water and accelerates bedrock weathering
influences on soil
ultimate driver is plate tectonics
younger soils influenced by the parent rock type
after time, climate is the strongest influence
temperate pedalfer types
defined horizon
A pedalfer is the dark, fertile type of soil that will form in a forested region.
desert pedocal types
A pedocal is the alkaline type of soil that forms in grassland regions.
drier, temperate areas
caliche layer
pedocal is named for the calcite enriched layer that forms. Water begins to move down through the soil layers, but before it gets very far, it begins to evaporate.
Soluble minerals, like calcium carbonate, concentrate in a layer that marks the lowest place that water was able to reach. This layer is called caliche.
tropical laterite types
A laterite is the type of thick, nutrient poor soil that forms in the rainforest.
hot, wet, tropical regions, intense chemical weathering strips the soils of their nutrient
practically no humus. All soluble minerals are removed from the soil and all plant nutrients are carried away
All that is left behind are the least soluble materials, like aluminum and iron oxides. These soils are often red in color from the iron oxides.
Soil Formation Factors
Thickness varies with - latitude topography resistance of parent rock duration of soil formation
Tropical Weathering and Laterite
Hydration, hydrolysis, dissolution and oxidation are maximised under warm wet conditions
mineral ‘leaching’ forms thick layers
Laterite
soil
saprolite
clay
unstable / stable minerals
unstable minerals (eg olivines, feldspars) stable minerals (eg iron and aluminium oxides, clays) The end-product (after 10s of 1000s of years) is bauxite or gibbsite
Desert Weathering
Thin soils
aridity + lack of vegetation
rare but violent rainstorms remove fine particles
Desert Weathering and caliche Concentration of broken bedrock and caliche
product of rare chemical weathering
2 processes and 2 products
1) Evaporation of sporadic near-surface percolating water
subsurface layers
2) Intense evaporation draws up water to the surface
irregular patches
Mass Wasting
Mass Movement
Much of the Earth’s surface is unstable - resulting in the downslope movement of blocks, regolith, soil, mud, snow, ice, etc
triggering event unnecessary
slope materials continually weathering and weakening
gravity operates all the time
Mass Wasting in rock cycle
Important to the rock cycle initial step in sediment transport significant agent of landscape change Major transport mechanism - sooner or later enters river systems shallow seas to the deep ocean
Slope Stability
Trade-off between - downslope force and resisting force downslope (weight) – rock or regolith water resisting force - cohesion chemical bonds electrostatic charges surface tension friction gentle and steep slope
Slope Stability influences
Angle of repose governed / influenced by particle size particle shape/surface roughness the coarser the grain the steeper the slope moisture, more moisture the less stable
Slope Destablilization
loading by water (rain) grains pushed apart → disintegration lubricates grain contacts/failure surfaces removal of vegetation slows water drainage destabilises soil erosion by excessive runoff steepening the slope by undercutting the foot initiates rockfall
Weak subsurfaces
failure surface
joints parallel to the surface
saturated sand or clay layers
weak sedimentary bedding (shales, evaporites)
metamorphic foliation
prefered orientation in a rock (foliation)
oversteepening and loading play a part
creep
creeping down a slope, not really important on large scale continuous in all terrestrial environments apart from deserts expansion and contraction freeze/thaw wet/dry grains move - perpendicular to slope (expansion) vertical (contraction) slope failure is rare
slump
initiated by earthquake
large mudslides
volcanic ash, rain, carry serious volume, short time on land, long ocean
