Geoscience processes shaping Earth's surface

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Constructive and Destructive Processes

**Constructive processes** (e.g., volcanism, deposition) build up Earth's surface by adding new rock or sediment.
**Destructive processes** (e.g., weathering, erosion) wear down or remove material from Earth's surface.
These processes operate over different time scales, from rapid landslides to slow mountain building.
Together, they shape landscapes such as mountains, valleys, and coastlines.

Weathering vs. Erosion

**Weathering** breaks down rock or soil in place, without movement.
**Erosion** removes and transports weathered material (sediment) from one location to another.
Physical (mechanical) erosion breaks rock into clastic sediment; chemical erosion dissolves material.
Erosion agents include water, wind, ice, gravity, and waves.

Agents of Erosion

**Water**: rainfall, surface runoff, rivers, and ocean waves erode and transport sediment.
**Wind**: abrasion and deflation remove loose particles, especially in dry regions.
**Ice**: glaciers pluck and scour rock as they move.
**Gravity**: mass movements like landslides and debris flows carry material downslope.
**Groundwater**: dissolves rock (e.g., limestone) to form caves and sinkholes.

Water Erosion Processes

**Splash erosion**: raindrop impact ejects soil particles up to 1.5 m horizontally.
**Sheet erosion**: thin overland flow transports loosened soil evenly across a slope.
**Rill erosion**: small, shallow channels (a few cm deep) form on hillslopes.
**Gully erosion**: concentrated runoff cuts deep channels (>1 ft² cross-section) that cannot be removed by tilling.
Extreme gully erosion can create **badlands** on easily eroded bedrock with sparse vegetation.

Deposition and Landforms

**Deposition** occurs when transported sediment is dropped in a new location due to loss of energy.
Rivers deposit sediment in **deltas** (at mouths) and **floodplains** (during floods).
Wind deposits fine sediment as **loess** or builds **sand dunes**.
Glaciers deposit unsorted material as **till** and sorted sediment as **outwash**.
Coastal deposition forms **beaches**, **spits**, and **barrier islands**.

Human Impact on Erosion

Human activities increase global soil erosion rates by **10–40 times** natural levels.
Intensive agriculture, deforestation, and construction accelerate erosion.
On-site effects: loss of fertile topsoil, reduced crop yields, and desertification.
Off-site effects: sedimentation of waterways, eutrophication, and damage to infrastructure.
Prevention practices include contour plowing, terracing, cover crops, and reforestation.

Factors Affecting Erosion Rates

**Slope steepness**: steeper slopes experience faster physical erosion.
**Climate**: rainfall amount, storminess, wind speed, and temperature influence erosion.
**Vegetation cover**: plants protect soil from raindrop impact and hold it with roots.
**Sediment load**: already transported sediment can reduce further erosion (feedback).

Four stages of water erosion: splash, sheet, rill, and gully.

Four main agents of erosion: water, wind, ice, and gravity.

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Practice questions

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1.What is the main difference between weathering and erosion?
Easy
- AWeathering involves the movement of rock, while erosion does not.
- BErosion involves the movement of rock or soil, while weathering does not.
- CWeathering is caused only by water, while erosion is caused by wind.
- DErosion only happens on steep slopes, while weathering happens everywhere.
2.Which of the following is NOT an agent of erosion?
Easy
- AWind
- BGlaciers
- CVolcanic eruption
- DRainfall
3.Which type of erosion is considered the first and least severe stage?
Medium
- AGully erosion
- BRill erosion
- CSheet erosion
- DSplash erosion
4.A farmer notices that after heavy rain, small channels that can be erased by normal tillage form in his field. What type of erosion is occurring?
Hard
- AGully erosion
- BRill erosion
- CSheet erosion
- DSplash erosion
5.What is the primary cause of accelerated soil erosion globally?
Medium
- ANatural climate change
- BHuman activities such as agriculture and deforestation
- CVolcanic eruptions
- DGlacial melting
6.Which of the following is an off-site effect of excessive erosion?
Medium
- ALoss of nutrient-rich topsoil
- BDecreased agricultural productivity
- CSedimentation of waterways
- DDesertification
7.In which type of erosion does runoff water accumulate and flow rapidly in narrow channels, removing soil to a considerable depth?
Hard
- ASheet erosion
- BRill erosion
- CGully erosion
- DSplash erosion
8.What percentage of global land degradation is caused by water and wind erosion combined?
Easy
- AAbout 50%
- BAbout 84%
- CAbout 70%
- DAbout 95%

Revision notes

## Geoscience Processes Shaping Earth's Surface ### Key Concepts - **Constructive processes** (e.g., volcanic eruptions, deposition) build up Earth's surface. - **Destructive processes** (e.g., weathering, erosion) wear it down. ### Erosion vs. Weathering - **Weathering**: breaking down of rock *in place* (no movement). - **Erosion**: removal and transport of material by agents like water, wind, ice, or gravity. ### Agents of Erosion - **Rainfall & runoff**: splash, sheet, rill, and gully erosion. - **Rivers & streams**: carry sediment downstream. - **Coastal waves**: wear away shorelines. - **Glaciers**: pluck and scour rock. - **Wind**: abrades surfaces in dry areas. - **Mass movement**: landslides, debris flows on steep slopes. ### Types of Water Erosion (in order of severity) 1. **Splash erosion**: raindrop impact ejects soil particles (up to 0.6 m vertically, 1.5 m horizontally). 2. **Sheet erosion**: thin layer of soil removed by overland flow. 3. **Rill erosion**: small, temporary channels (a few cm deep) form. 4. **Gully erosion**: deep channels (>1 ft² cross-section) that cannot be removed by tilling; can lead to badlands. ### Factors Affecting Erosion Rate - Slope steepness (faster on steeper slopes) - Climate (rainfall amount, storminess, wind speed, temperature) - Vegetation cover (plants protect soil) - Human activities (farming, deforestation, construction) ### Human Impact - Human activities increase erosion rates by **10–40 times** globally. - In the Appalachian Mountains, intensive farming causes erosion up to **100 times** the natural rate. - **On-site effects**: loss of fertile topsoil, reduced crop yields, desertification. - **Off-site effects**: sedimentation of rivers, eutrophication (nutrient pollution), damage to infrastructure. ### Prevention & Remediation - Practices like contour plowing, terracing, cover crops, and reforestation help limit erosion. ### Key Terms - **Deposition**: the process of eroded material being dropped in a new location. - **Sediment**: particles of rock or soil carried by erosion. - **Badlands**: severely eroded landscapes with steep slopes and little vegetation.

Erosion: The removal and transport of soil, rock, or dissolved material from one location to another by surface processes such as water flow, wind, or ice.
Weathering: The breakdown of rocks and minerals at the Earth's surface through physical or chemical means, without movement.
Deposition: The process by which eroded material is dropped and accumulates in a new location.
Splash erosion: The first stage of soil erosion caused by the impact of raindrops, ejecting soil particles up to 0.6 m vertically and 1.5 m horizontally.
Sheet erosion: The removal of a thin, uniform layer of soil by overland flow of water.
Rill erosion: Erosion that forms small, temporary channels (a few cm deep) on hillslopes, acting as sediment sources and delivery paths.
Gully erosion: Severe erosion where runoff creates deep channels (cross-section ≥1 ft²) that cannot be erased by normal tillage, potentially leading to badlands.
Sediment: Solid fragments of rock, soil, or organic material that are transported and deposited by erosion.
Eutrophication: Excessive nutrient enrichment of water bodies, often caused by sediment runoff from erosion, leading to algal blooms and oxygen depletion.
Badlands: Highly eroded landscapes with steep slopes, sparse vegetation, and easily eroded bedrock, formed by extreme gully erosion.

Flashcards

What is the difference between weathering and erosion?

Weathering involves breaking down rocks without movement, while erosion involves moving the broken material from one place to another.

Name four agents of erosion.

Water (rainfall, rivers, waves), wind, glaciers, and gravity (mass movements like landslides).

What are the four main types of soil erosion caused by rainfall?

Splash erosion, sheet erosion, rill erosion, and gully erosion (in order of increasing severity).

Describe splash erosion.

Splash erosion occurs when raindrops hit the soil, creating small craters and ejecting soil particles up to 0.6 m vertically and 1.5 m horizontally.

What is sheet erosion?

Sheet erosion is the transport of loosened soil particles by overland flow (surface runoff) in a thin, uniform layer.

What is rill erosion?

Rill erosion is the development of small, concentrated flow paths (rills) on hillslopes that carry sediment; flow depths are typically a few centimeters.

What distinguishes a gully from a rill?

A gully has a cross-sectional area of at least one square foot and cannot be erased by normal tillage, while a rill is smaller and can be smoothed by tillage.

How do human activities affect erosion rates?

Human activities have increased global soil erosion rates by 10–40 times; in some areas like the Appalachian Mountains, farming has caused erosion up to 100 times the natural rate.

What are two on-site impacts of excessive erosion?

Decreased agricultural productivity and ecological collapse due to loss of nutrient-rich topsoil.

What are two off-site impacts of excessive erosion?

Sedimentation of waterways and eutrophication of water bodies, plus damage to roads and houses.

What percentage of global land degradation is caused by water and wind erosion combined?

About 84%.

What is deposition?

Deposition is the arrival and emplacement of eroded material at a new location after transport.

List three human activities that stimulate erosion.

Intensive agriculture, deforestation, and construction of roads.

What is the difference between physical (mechanical) erosion and chemical erosion?

Physical erosion removes rock or soil as clastic sediment; chemical erosion removes material by dissolution.

How does slope steepness affect erosion rates?

Physical erosion typically proceeds fastest on steeply sloping surfaces.

What climatic factors influence erosion rates?

Amount of water (rain), storminess, wind speed, wave fetch, and atmospheric temperature (especially for ice-related processes).

What is the most severe stage of soil erosion by water?

Gully erosion.

What conditions lead to badland formation?

High relief, easily eroded bedrock, favorable climate for erosion, and limited protective vegetation (rhexistasy).

What is the difference between splash erosion and sheet erosion?

Splash erosion is caused by raindrop impact ejecting soil particles; sheet erosion is the transport of loosened particles by overland flow.

What is the primary cause of land degradation worldwide?

Water and wind erosion, responsible for about 84% of degraded land.

How far can soil particles travel during splash erosion?

Up to 0.6 m vertically and 1.5 m horizontally on level ground.

What is rhexistasy?

Conditions or disturbances that limit the growth of protective vegetation, contributing to badland formation.

What is the difference between a rill and a gully in terms of tillage?

A rill can be erased by normal tillage; a gully cannot.

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