ch 8 weathering, soil, and mass wasting

weathering - disintegration and decomp of material at or near the surface

mass wasting - transfer of rock material downslop under the influence of gravity

erosion - transportation of material by a mobile agent, usually water, wind, or ice

external processes - owered by gravity and sun

internal processes - powerd by earth’s interior

types of weathering

1. mechanical

   • breaking rocks into smaller pieces which makes more surface area, which increases chance of chemical weathering

2. chemical

   • chemical transformation of rock into one or more new compounds

   • alters the internal structures of minerals by removing or adding elements

   • most important agent is water: oxygen dissolved in water oxidized materials, and co2 dissolved in water forms carbonic acid and alters materials

   • calcite is most easy to be dissolved into water

   • quartz is very resistent

mechanical weathering processes

• frost wedging: expansion of freezing water. water expands at 9% when frozen. can create a talus slope

• sheeting: generates onion-like layers and exfoliation domes. flakey

• biological activitiy: plants dig into rock, they can produce acids that promote decomp, and bacteria can eat rock

• salt crystal growth: sea sprayh goes into rock pores, when water evaporaes, crystals enlargen and rock breaks

• root wedging

chemical weathering processes

• spheroidal: generates rounded rocks, weathering works inward from exposed surfaces or cracks, joshua tree np is granite rock

• oxidysing: turns into rusty red orange color

• rusting/oxidizing

rates of weathering

• advanced mechanical weathering aids chemical weathering by increasing surface area

• mineral comp and solubility

  • EX: granite is less impacted by weathering than than marble

• physical features like joints

• climate - temp and moisture

  • chemical weathering is most effective in warm temps with a lot of moisture

  • physical weathering is more common in mountains and deserts

• differential

  • caued by variations in comp. / made of diff materials

  • creates weird rock shapes/landforms/formations

soil: combonation of mineral matter, water, and air

• interface in the earth system

• most impacted by parent material

• regolith: what soils are made of. rock and mineral fragments which support the growth of plants

• 45% mineral matter + humus

• 25% air

• 25% water

• 5% organic matter

soil texture: refers to the diff proportions of diff particle sizes

• sand - large

• silt - medium

• clay - small

loam:

• nearly equal amounts of clay, silt, and sand.

• best suited for plant life

soil structure:

• soil particles clump together to give soil its structure

• basic structures

  • platy

  • prismatic

  • blocky

  • spheroidal

  • massive

controls of soil formation

• parent material

  • residual soil - parent material is the bedrock

  • transported soil - parent materials have been carried from smoewhere and deposited

• time

  • important to all geologic processes

  • amount of time to evolve varies for different soils

• climate

  • most important control of soil type

  • humidity or temp increat and increase breakdown of organic and inorganic materials

• plants and animals

  • organisms influence soil’s phys and chem properties

  • furnish organic matter to soil

• slope

  • angle: steep slopes have poorly developed soils. optimum is a flat-to-undulating upland surface

  • orientation (direction slope is facing): influences soil temp and moisture

soil profile

• soil forming processes operate from surface downward

• horizons - zones or layers of soil

horizons in temperate regions

O - organic matter

A - organic and mineral matter

E - little organic matter, eluviation and leaching

B - zone of accumulation

C - partially altered parent material

top soil

• zones O and A

solum

• “true soil”

• O, A, E, B

soil taxonomy - soil classification

• emphasized phys and chem properties of soil profile

• soil units are combos of syllables of latin and greek origin

soil erosion - recycling of earth materials

• natural part of earth’s systems

• natural rates depend on

  • soil characteristics

  • climate

  • slope

  • type of vegetation

processes that erode soil

• water erosion

  • raindrops dislodge soil particles

  • flowing water carries soil away

  • 2/3 of all us soil erosion

• wind erosion

  • occurs with dry soil conditions

soil erosion control

• leave steep slopes undistrubed

• terrace crop planting

• grassed waterways

• tree windbreak barriers

• not logging

mass wasting: the downslope movement of rock, regolith, and soil under the direct influence of gravity

triggers

• saturation of material with water

  • destroys particle cohesion

  • water adds weight

• over steepening of slopes

  • unconsolidated granular particles assume a stable slope called angle of repose. the steepest angle which loose material won’t slide down the slope

  • stable slope angle is diff for diff materials

• removing anchoritng vegetation such as fire

  • important bc roots anchor the soil

• earthquakes

  • ground vibrations can reduce natural soil stability

mass wasting process

1. material involved

   • debris

   • mud

   • earth

   • rocks

2. types of movement

   • fall (free fall)

   • slide (material moves along a well defined surface)

   • flow (material moves as a viscous fluid)

3. rate of movement

   • fast

   • slow

mass wasting forms

• rock fall: often seen i mountains areas and happens rapidly. boulders fall down

• rockslide: rabid and blocks of bedrock move down a slope

• slump (types of slide): rapid movement along a curved surface that ofccur along over steepened slopes

• debris flow/mudflow: rapid flow of debris with water, often confined to channels, composed mostly of volcanic materials called lahars

• earthflow: rapid water that saturates the soil and typically occurs on hillsides in humic regions

  • liquefaction: special types of earthflow sometimes associated with earthquakes

• creep: slow movement of soil and regolith downhill that causes fences and utility poles to til over time

• solifluctioin: slow movment in areas underlain by permafrost

  • upper active soil layer becomes saturated and slowly flows over a frozen surface below

  • most common in permafrost zone where ground stays permanently frozon but buildings are warmer

• slide: refers to mass movements in which there is a distinct zone of weakness separating the slide material from the more stable underlying material. Movement does not occur on a curved surface.

• slump: involves a downward sliding of a mass of rock or unconsolidated material moving as a unit along a curved surface—creating a crescent shape at the head.

• fall: occurs when the movement in a mass-wasting event involves the free fall of detached individual pieces of any size. This occurs on very steep slopes.

• creep: involves the gradual downhill movement of soil and regolith. causes fences and utility poles to tilt over time

• flow: occurs when material moves downslope as a viscous fluid. lots of water

alluvial fan: A fan-shaped deposit of sediment formed when a stream’s slope is abruptly reduced. not a ceiling fan, more like a hand held fan

talus slope: composed of angular rock fragments. looks like a very steep, smooth. located at the base of cliffs

retaining wall: a wall that holds back stuff from collapsing

porosity: volume of open spaces in rock or soil

differencial weazthering: variation of rate and degree of weathering

chem qeatherin g most effective in warm temp + humidity