Erosion and Weathering (IB Geography)

What is weathering?

The breakdown of rocks and minerals at or near Earth’s surface through physical, chemical, or biological processes without movement of the material.

What is erosion?

The process by which weathered rock and soil are moved from one place to another by agents like water, wind, ice, or gravity.

How does weathering differ from erosion?

Weathering breaks rocks down in place, while erosion moves the broken material elsewhere.

Mechanical (physical) weathering

The breakdown of rock into smaller pieces without changing its chemical composition.

Chemical weathering

The breakdown or decomposition of rocks due to chemical reactions that change their composition.

Biological weathering

The breakdown of rocks caused by living organisms such as plants, animals, and microbes.

Frost wedging (freeze-thaw action)

water enters cracks, freezes, expands, and causes the rock to break apart.

Thermal expansion

Repeated heating and cooling that causes rock to expand and contract, eventually fracturing it.

Abrasion

The mechanical scraping of a rock surface by friction or impact from particles carried by wind, water, or ice.

Exfoliation (spheroidal weathering)

temperature variations cause rock minerals to expand and contract at different rates gradually splitting apart the rock. In humid climates, running water tends to round off the surface features causing the "skin" of the rock to peel off.

Hydrolysis

Chemical weathering where minerals react with water to form new minerals and dissolve ions.

Oxidation

Chemical weathering involving the reaction of minerals with oxygen, forming oxides (e.g., rusting of iron).

Carbonation

Process where carbon dioxide dissolves in water to form carbonic acid, which reacts with rocks like limestone.

Acid rain

Rainwater containing acids from pollutants that accelerate chemical weathering.

Root wedging

Type of biological weathering where plant roots grow into cracks in rocks, forcing them apart.

Can moss and lichen weather?

Yes, they can weather physically by growing and chemically by excreting acid

Factors affecting rate of weathering

Rock type, climate, surface area, and presence of soil or vegetation.

How does climate affect weathering?

Warm, wet climates promote chemical weathering; cold climates favor mechanical (freeze-thaw) weathering.

What role does surface area play in weathering?

Increased surface area (more exposed rock) leads to faster weathering.

What are the main agents of erosion?

Water, wind, ice (glaciers), and gravity.

What is mass wasting?

The downhill movement of weathered material due to gravity (e.g., landslides, slumps, creeps).

Describe a landslide.

A rapid downslope movement of rock and soil triggered by factors like rain, earthquakes, or human activity.

What is soil creep?

The very slow movement of soil down a slope due to gravity.

What is a slump?

A rotational mass movement where a section of land slips down along a curved surface.

Describe fluvian transport (and erosion)

Streams and rivers carry sediments that abrade rock and transport material downstream.

What is a floodplain?

The flat area adjacent to a river that is periodically flooded, where sediments are deposited.

How do rivers create valleys?

Through vertical erosion that deepens the channel and lateral erosion that widens it over time.

What are meanders?

Curving bends in a river formed by erosion on the outer bank and deposition on the inner bank.

What is a delta?

A depositional landform formed at a river’s mouth when sediment is deposited faster than it can be removed.

Glacial erosion

Occurs when glaciers move downhill, scraping and grinding the underlying rock.

Plucking and abrasion (glacial processes)

Plucking: glacier freezes onto rock and pulls pieces away; Abrasion: embedded rocks grind surfaces smooth.

Aeolian Transport

Movement of particles by wind through processes like deflation and abrasion.

Deflation

Removal of loose particles by wind, leaving behind coarser materials (desert pavement).

Loess

Fine, wind-blown sediment that can form fertile soils.

Coastal erosion

Wearing away of land along coastlines by wave action, currents, and tides.

Hydraulic action (waves)

The force of waves compressing air into cracks in coastal rocks, causing them to break apart.

Abrasion (coastal)

Waves carrying sand and pebbles grind away the rock surface.

Attrition

Rocks and pebbles collide, breaking into smaller, smoother pieces.

Coastal solution

Chemical action where sea water dissolves certain rock types like limestone.

Deposition

The laying down of eroded material when the energy of the transporting medium decreases.

Alluvial fan

A fan-shaped deposit formed where a river slows down at the base of mountains.

How are caves formed?

By chemical weathering (carbonation) dissolving limestone underground.

Karst topography

A landscape shaped by chemical weathering of limestone, featuring caves, sinkholes, and disappearing streams.

Sinkhole

A depression formed when the roof of an underground cavity collapses.

How do human activities accelerate erosion?

Deforestation, overgrazing, construction, and poor farming expose soil to erosion agents.

Soil erosion prevention methods

Planting vegetation, terracing, contour plowing, and windbreaks.

What is differential weathering?

When softer rock erodes faster than harder rock, creating features like cliffs and arches.

What is sediment?

Small particles of rock, minerals, and organic material transported by erosion.

What is sedimentation?

The process of settling or depositing sediments in a new location.

Describe the process of the rock cycle involving weathering and erosion.

Weathering breaks down rock; erosion transports particles; deposition creates sedimentary rocks over time.