Section L: Weathering and Mass Wasting

what is geomorphology

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

what is a landform

a natural feature created by weathering and natural processes

what is a landscape

a collection of similar landforms

what is denudation

the disintegration (wearing away) and overall lowering of continental surfaces

what three activities are involved in denudation

1. weathering - breaks rocks down into smaller pieces

2. mass wasting - movement downslope over a short distance

3. erosion (gravity, wind, water, ice) long distance movement

what are joints

openings (typically microscopic) in surface allow weathering agents to transfer deeper into rock (water, air, plant roots)

how does bedrock get destroyed

through weathering - fragments into smaller pieces (any exposed bedrock is weathered)

in colder, drier climates, what kind of weathering is more common

physical weathering

in warmer, wetter climates, what kind of weathering is more common

chemical weathering

what is differential weathering

when some rocks are more resistant to weathering than others.

• limestone is resistant to physical weathering

• sandstone has variation in the cementing materials, leading to unusual landforms where the rock weathers at different rates

what is caprock

more resistant rock overtop of less resistant rock. protects the under rock a bit

what is mechanical (physical weathering)

the physical disintegration of rock with no change in its chemical composition. it increases surface area for chemical weathering

what is frost wedging/shattering/action

the freezing and thawing action of water. ice wedges downward into openings, ice melts and water falls farther into larger opening. the process repeats

what is a talus slope (scree)

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

what is salt wedging

growth of salt crystals

• water carries salts in solution

• water evaporates and salt is left behind

• rock disintegrates grain by grain

what is chemical weathering

the chemical alteration and decomposition of rock minerals, enhanced by mechanical weathering.

what two things does chemical weathering need to occur

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

where do we see high and low rates of chemical weathering

• high rates: warm, moist environments - wet tropics

• low rates: cold lands and deserts

what are the two most significant processes of chemical weathering

hydrolysis and carbonation and solution

what is hydrolysis

the change in chemical structure of mineral after water is added to a compound, creating softer and bulkier and more susceptible to erosion. water loosens a mineral’s chemical bonds and produces a different material

what type of rock is most susceptible to hydrolysis

igneous rocks because of their silicates

what ions in water are responsible for hydrolysis

hydrogen ions (H+) and hydroxide ions (OH-)

what is spheroidal weathering

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

how is carbonic acid formed

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

what is dissolution

when rocks dissolve when exposed to the water/acid combination. weak carbonic acid solution causes carbonate rocks (limestone) to dissolve and wash away

what is the chemical formula for carbonation and dissolution

CaCO₃ + H₂CO₃ → Ca(HCO₃)₂

• calcium carbonate (calcite) + carbonic acid = bicarbonate ions

what is biological weathering

plants and animals alter rock structure, impacts of lichens, burrowing animals, human activity

what is karst topography

it develops because of sub surface dissolution and forms in thick deposits of limestone. landforms include caves, sinkholes, and other soluble rock features

what is carbonation in chemical weathering

the process where carbonic acid dissolves minerals, especially limestone, leading to chemical weathering

is limestone more resistant to mechanical or chemical weathering

limestone is resistant to mechanical weathering but highly vulnerable to chemical weathering through carbonation

why is limestone vulnerable to carbonation

because it’s composed of mainly calcium carbonate which reacts with carbonic acid, leading to dissolution

why is underground water considered a weak carbonic acid solution

it contains dissolved co2, which reacts with water to form carbonic acid, making it slightly acidic

which types of rocks are most affected by dissolution

carbonate rocks, such as limestone, gypsum and dolomite

what happens to elements in a high pressure or high temperature envr

elements remain dissolved in water and stay in solution

what causes calcium bicarbonate to precipitate out of solution

a change in air pressure when water enters a cave

what mineral forms when calcium bicarbonate precipitates

calcium carbonate gets deposited as the mineral calcite

what are speleotherms

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

what is dripstone

water drips and calcite is deposited

• stalactite - hangs from roof

• stalagmite - projects up from the floor

what is flowstone

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

• flowstone forms sheet-like formation on floor or walls

why are joints important

they act as solution pathways for water, leading to karst formation

what are sinkhole (dolines) and how do they form

they’re depressions in cavernous limestone, forming when caves collapse or groundwater is excessively extracted

what are disappearing streams

surface streams that flow into sinkholes and enter underground channels

what are springs in a karst landscape

locations where groundwater naturally emerges at the earth’s surface

what is a tower karst

a dramatic form of karst topography with tall, steep limestone towers, found in humid subtropical regions

what conditions lead to tower karst formation

thick limestone beds, high water tables, long term dissolution processes

how do tower karst landscapes form

over time, caves and passageways enlarge and collapse, leaving behind isolated limestone towers

what do unaffected limestone blocks form in tower karst areas

they create the appearance of towering hills or haystack formations

what is a sinkhole plain

a region of classic karst topography with dozens of sinkholes and disappearing streams

what is mass wasting

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

what factors influence mass wasting

1. angle of repose - the steepest angle that can be assumed by loose fragments without moving downhill

2. influence of water - if water is added (rain, snowmelt), rock fragments are more likely to move. decreases friction/cohesion as water lubricates the particles

what are the four types of mass wasting

rock fall, landslide, soil creep and flows

what is rock fall and what is it driven by

it’s the rapidly dropping, bouncing or rolling descents of material, mainly through the air, from cliffs and other steep slopes. it’s largely driven by freeze-thaw. (fastest mass wasting)

what are landslides

movement downslope. slope failure involving the collapse of a slope and movement along a flat, sliding plane.

• large rigid mass (no fluid flow)

• often with heavy rains or an earthquake (at the start) but then it falls dry

what are some effects of landslides

• 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 a soil creep

• slowest mass wasting

• particle by particle movement

• freeze-thaw/wet-dry conditions

• any action that disturbs surface

• displacement of human structures

what is flow mass wasting

a section of a slope becomes unstable with the absorption of water and so flows downhill. ranges from fairly rapid to gradual and sluggish. center moves more rapidly than the base and sides

what is the size of flows

relatively small, often taking up an area only a few square meters. or they cover tens or hundreds of hectares. relatively shallow.

what is earthflow

a portion of a water saturated slope moves a limited distance downhill, normally during or immediately after a heavy rain

what is mudflow

originates in drainage basins when a heavy rain, often following a long dry spell, produces a cascading runoff too great to be absorbed into the soil