Section L - Weathering and Mass Wasting

What is geomorphology?

the study of the processes shaping earth’s surfaces and the landforms and deposits they produce

What is landform? (+ examples)

• specific natural physical features of the earth’s surface

  • mountains, valleys, hills, skull rock

what are landscapes?

• encompass the visible features of the area

  • view of San Andreas fault and valley from lookout in Joshua Tree

What is denudation?

disintegration (wearing away) and overall lowering of continental surfaces

Denudation involes which 3 activities?

• weathering

• mass wasting

• erosion

  • gravity, wind, water, ice, etc

The walls of Grand Canyon of the Colorado River are a result of the forces of _ and _

• weathering

• mass wasting

What is weathering?

• breakdown of rock in-situ (‘in place’)

  • physical, chemical, biological

What is mass wasting

• gravity, short distance

  • slope process

What is erosion?

• removal/ transportation

  • running water, glaciers, wind, coastal waves

What are the geomorphological agents? (5)

• gravity

• water

• glaciers

• wind

• waves

Weathering destroys _ and _ into smaller pieces

• bedrock

• fragments

Any exposed bedrock is _

weathered

What are joints?

• openings (typically microscopic) in surface allow weathering agents to transfer deeper into rock

  • water, air, plant root

Why are joints important?

they act as the primary conduits for agents of erosion, fundamentally weakening rock masses and providing the planes of weakness necessary for slope failure

Colder/ drier climates tend to have:

more physical weathering

Warmer/ wetter climates tend to have:

more chemical weathering

What is differential weathering?

some rocks are more resistant to weathering

What rock is more resistant to physical weathering?

limestone

What has variation in the cementing materials, leading to unusual landform where the rock weathers at different rates?

sandstone

What is caprock?

more resistant rock over less resistant rock

Mechanical (physical) weathering is: (3)

• physical disintegration of rock

• no change in its chemical composition

• increases surface area for chemical weathering

Type of physical weathering:

frost wedging/ shattering/ action

What is frost wedging? (4)

• process of freezing and thawing action of water

• ice wedges downward in openings

• ice melts and water falls farther into larger opening

• process repeats

What happens to water from the frost wedging process at 4-0 degrees C

water expands 9%

What is talus slope (scree)?

a pile of weathered rock that accumulates close to the mountain wall through numerous small rocks falls

Talus cones on north shore of:

Isfjord, Svalbard, Norway

What is salt wedging? -cause growth of salt crystals- (3)

• water carries salts in solution

• water evaporates and salt left behind

• rock disintegrates grain-by-grain

What is chemical weathering?

chemical alteration of rock minerals, enhanced by mechanical weathering

Chemical weathering need:

exposed bedrock (fine-grain material decomposes faster) and moisture

Rates of chemical weathering (2)

• high rates: warm, moist environments -wet tropics

• low rates: cold lands and deserts

Most significant processes of chemical weathering (2)

1. hyrodolysis

2. carbonation and solution

In which process: change the chemical structure of mineral, creating softer and bulkier and more susceptible to erosion

hydrolysis

Which process: dissolves minerals, washing them away in runoff

carbonation and solution

Hydrolysis is the reaction of:

any substance with water

During hydrolysis, water loosens a mineral’s chemical bonds and produces:

a different mineral

Water dissociates into H+ ions and OH- ions: (2)

• hydrogen and hydroxide

• replace ions in a mineral

Spheroidal weathering results from:

hydrolysis that works on the weaker, sharp edges and corners of rocks, rounding them

What happens during carbonation

water reacts with carbon dioxide to produce a weak solution of carbonic acid

Dissolution (2)

• rocks dissolve when exposed to the water/ acid combination

• weak carbonic acid solution causes carbonate rocks (e.g. limestone) to dissolve and wash away

Formula of carbonation and dissolution of chemical weathering

calcium carbonate/ calcite + carbonic acid → bicarbonate ions

CaCO₃ + H₂CO₃ → Ca(HCO₃)₂

What and how are sinkholes formed?

a sinkhole is a depression or hole in the ground caused by the collapse of the surface layer, often due to the dissolution of underlying soluble rock

Sinkholes in different areas in Florida (3)

• Winter Park

• Tampa

• Sebring

Sinkholes in Sebring, Florida

left it buckled in the middle and full of water

Biological Weathering (2)

• weathering caused by organisms

• can be either physical and/or chemical

Factors to biological weathering (4)

• plants and animals alter rock structure

• impacts of lichens

• burrowing animals

• human activity

Why does karst topography develop

dissolution

Where do karst topography form?

in thick deposits of limestone

Karst topography landforms include: (3)

• caves

• sinkholes

• other soluble rock features

Major karst regions in the world

two process of

Carbonation

underground water is a weak solution of carbonic acid

Carbonic acid (H₂CO₃) is a mild acid that is formed when?

carbon dioxide dissolves in water

Limestone is resistant to mechanical weather but vulnerable to:

chemical weathering (carbonation)

Dissolution affects all rocks, particularly carbonate rocks like:

limestone

Limestone is composed of _ _ which reacts with weak _ _ solution to yield _ _, a compound soluble to water (and removed by water)

• calcium carbonate

• carbonic acid

• calcium bicarbonate

Other carbonate rocks (gypsum or dolomite) will also undergo _

dissolution

In a high pressure or high temp environment, elements _ in solution with water

remain

Once the water enters a cave, the air pressure changes, how? (2)

• calcium bicarbonate precipitates out of solution

• calcium carbonate gets deposited in the cave as the mineral calcite

Precipitate formation in caves (3)

• speleothems

• dripstone

• flowstone

What is speleothems?

precipitated mineral deposits (usually calcite, the mineral that forms from calcium carbonate) on walls, roof or floor of cave

What is Dripstone? (3)

• water drips and calcite is deposited

• stalactite

  • hangs from the roof

• stalagmite

  • projects up from the floor

What is flowstone? (2)

• where water flows along a wall, ceiling or floor and calcite is deposited

• flowstone forms sheet-like formation on floor or walls

What is the role of bedrock structure?

cracks, known as joints, becomes solution pathways

Sinkholes (dolines) are depressions that occur in regions of cavernous limestone, form when:

caves enlarge and their ceiling collapses or when ground water is excessively extracted

Disappearing streams are surface flows that go down into a sinkhole, entering what?

underground channels

_ are locations where ground water emerges at the surface of the earth

springs

Tower karst

spectacular form of karst topography that can occur in humid subtropical areas with thick limestone beds and high-water tables

Tower karst

spectacular form of karst topography that can occur in humid
subtropical areas with thick limestone beds and high-water tables

Mass wasting

spontaneous downhill movement of soil, regolith and bedrock under the influence of gravity

Factors influencing mass wasting (2)

• angle of repose

• influence of water

Mass wasting: Angle of repose

the steepest angle that can be assumed by loose fragments without moving downhill

Mass wasting: Influence of water (2)

• if water is added (rain, snowmelt, etc.), rock fragments are more likely to move (especially if small)

• decreases friction/ cohesion as water lubricates the particles

Slope stability: friction >/= gravity

rock does not move

Slope stability: friction < gravity

rock moves

Types of mass movements (4)

• rock fall

• landslide

• soil creep

• flows

What is rock fall?

rapidly dropping, bouncing, or rolling descents of material, mainly through the air, from cliffs and other steep slopes

What is rock fall largely driven by?

freeze-thaw

What is movement downslope?

• slope failure involving the collapse of a slope and movement along a flat, sliding plant

  • large rigid mass (no fluid flow)

  • often with heavy rains or an earthquake

Landslide effects (3)

• scar on hill where slide originated

• debris at base of slope piles up

• natural dam may form in valley, blocking stream and creating lake

What is the slowest mass wasting process

soil creep

Soil creep has a _-by-_ movement

particle by particle

Soil creep conditions:

freeze-thaw/ wet-dry

Soil creep: any action that disturbs _

surface

Soil creep: displacement of:

human structures

Complex debris flow

landslide → crossed river → high speed debris avalanche → water-saturated debris flow

Damage of Oso, Washington Debris-Avalanche Flow on May 22,2014 (2)

• 43 fatalities

• 40 houses destroyed