Weathering, Erosion, and Mass Movement

Question 1

Define weathering

Answer 1

physical breakdown and chemical alteration of rock at or near Earth’s surface

Question 2

What are the two kinds of weathering?

Answer 2

Mechanical and Chemical

Question 3

Mechanical Weathering

Answer 3

physical forces breaking rock into smaller pieces

Question 4

Chemical weathering

Answer 4

chemical transformation of rock into new compounds

Question 5

True or False: Both kinds of weathering work simultaneously and reinforce each other?

Answer 5

True

Question 6

True or False: Mechanical weathering increases surface area?

Answer 6

True

Question 7

What is the relation between mechanical and chemical weathering

Answer 7

as mechanical weathering breaks rocks into smaller pieces, more surface area is exposed to chemical weathering

Question 8

Types of mechanical weathering

Answer 8

• Frost wedging
• Sheeting/unloading
• Biological Activity
• Salt crystal growth

Question 9

Frost wedging

Answer 9

• water that freezes in cracks enlarges the cracks

- lenses of ice increase in size as they attract liquid water

Question 10

Unloading/Sheeting

Answer 10

• unloading leads to sheeting

- concentric slabs break loose when large masses of igneous rock are exposed due to erosion and glaciation.

Question 11

How does an exfoliation dome form?

Answer 11

-continued weathering causes slabs to fall off and form a EXFOLIATION DOME

Question 12

What are joints?

Answer 12

Joints are fractures produced by contraction during the crystallization of magma

Question 13

Biological growth

Answer 13

• PLANT ROOTS grow into fractures in rocks, expanding cracks

- BURROWING ANIMALS move fresh material to the surface, enhancing mechanical and chemical weathering

Question 14

Types of Chemical Weathering

Answer 14

• Dissolution
• oxidation
• hydrolysis
• spheroidal weathering

Question 15

What is the most important agent in chemical wearthing?

Answer 15

Water

Question 16

Three things about Dissolution

Answer 16

A small amount of acid in water is responsible for the corrosive properties

• CO2 dissolved in rain=carbonic acid
• Calcite (CaCO3) is particularily susceptible to weakly acidic solutoin

Question 17

Three things about Oxidation

Answer 17

rust (iron oxide) forms when O2 combines with Fe

• water catalyses the rxn
• important in decomposing ferromagnesium minerals (olivine, pyroxene, hornblende, and biotite)

Question 18

Two things Hydrolysis

Answer 18

• any rxn with water

- silicates (clay) decompose via hydrolysis

Question 19

True or False: Clay minerals are the most abundant product of weathering

Answer 19

true

Question 20

Spheroid weathering (3)

Answer 20

1) water penetrates jointed rocks
2) chemical waethering decomposes minerals and enlarges joints
3) rocks are attacked around the corners and edges, producing spherical shapes and fragments

Question 21

What influences the rate of weathering

Answer 21

Rock Type and Climate

• silicate minerals weather in same order as Bowen’s rxn series (Olivine –> pyroxine –> amphibole –> biotite etc)
• warm/moist climates enhance weathering
• cold/dry climates inhibit

Question 22

Differential Weathering

Answer 22

uneven weathering due to different mineral composition

Question 23

Examples of differential weathering

Answer 23

Soil

-portion of regolith that supports growth of plants

Question 24

Define regolith

Answer 24

Mineral fragments that cover the surface of earth

Question 25

Impact of human activity on soil

Answer 25

soil erosion (loss of topsoil) -enhanced by deforestation and farming soil conservation -planting in patterns that follow contour of landscape reduces rate of water runoff -grassed waterways between crops prevetns formation of gullies and traps soil washed from cropland

Question 26

True or False: Weathering and erosion are slow processes (snail)

Answer 26

true

Question 27

Define Mass Movement

Answer 27

movement of bedrock, rock debris, or soil downslope due to gravity -ie. landslide

Question 28

What is the main driving force of mass movement?

Answer 28

erosion agents (weathering, erosion etc)

Question 29

Gravitational Driving Force

Answer 29

F(drive)=m*a=m*g

Question 30

Friction and Cohesion RESISTING FORCE

Answer 30

F(res)= mu(fric)*mg*cos(theta) | F(res)=basal friction+internal strength

Question 31

Shear deformation

Answer 31

internal deformation (flow) due to gravity

Question 32

Factors that influence internal strength of rock debris, sediment, or soil

Answer 32

1) electrostatic forces (ie. clay particles) 2) friction @ grain contact=f(angularity, grain size) 3) pore pressure 4) surface tension (wet sand-->dry sand-->damp sand) (in order of increasing cohesion)

Question 33

Define Angle of repose

Answer 33

increase with grain size - fine sand (round): 35 degrees - fine sand (angluar): 40 - course sand: 45

Question 34

What makes a slope SUSCEPTIBLE to mass movement

Answer 34

1) slope angle 2) relief 3) bedrock type (ie. jointed, fractured, bedded) 4) thickness of debris (ie. soil cover) 5) climate - a) ice (freeze-thaw cycle) - b) water/moisture - c) rain - d) vegetation (low cover)

Question 35

What TRIGGERS mass movement

Answer 35

- heavy rainfall/snowmelt - addition of buildings - earthquakes/explosions/eruptions - excavation/road construction/ river erosion

Question 36

Falls

Answer 36

Rock: rockfall, very fast Debris: debrisfall, fast-very fast

Question 37

Slide

Answer 37

Rock: rockslide, fast Debris: -slump (rotational), slow-moderate -debris slide (translational), slow-fast

Question 38

Flow:

Answer 38

``` Rock: -creep, very slow (10 cm/yr) Debris: -creep, very slow (,10 cm/yr) -Earthflow/gelifluction/debris flow/mudflow/quick clays, mod-fast -avalanche, very fast - ```

Question 39

creep

Answer 39

very slow Mechanisms: -wet/dry cycle -freeze/thaw cycle

Question 40

gelifluction

Answer 40

in colder climate: H2O saturated debris moves over permafrost during warmer months

Question 41

Debris flow

Answer 41

course material (boulder/gravel) is predominant, supported by matrix of finer sediment

Question 42

mudflow

Answer 42

mix of debris and water, confined by chanel - faster/further than debris flow - high water content

Question 43

Where do mudflows occur

Answer 43

flanks of volcanoes, steep deforested mountain sides, steepened cliffs of unconsolidated fine sediment

Question 44

True or False; Pyroclastc flows (ash, hot gases, sediment) turn into mudflows (sediment and water) downstream

Answer 44

true

Question 45

Quickclays

Answer 45

- clays deposited in laciomarine environments | - decreased stability when salt is leached out by freshwater

Question 46

Clay mineral formation

Answer 46

orthoclase feldspar + acid+ water = clay + potassium + soluble silica (2KAlSi3O8 + 2H+ + 9H2O = Al2Si2O5(OH)4 + 2K+ + 4H4SiO4)

Question 47

What is the relative rate of weathering of common minerals?

Answer 47

most stable to least stable; Iron oxide, aluminum hydroxides, quartz, clay minerals, musovite mica, potassium feldspar, boilite, albite, amphiboles, pyroxene, anorthite, olivine, calcite, halite.