Earth Science: Weathering and Erosion

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Questions and Answers

What is the main energy source that powers external processes on Earth?

Energy from the sun (correct)

Wind patterns

Geothermal energy

Tidal forces

Which process involves the physical breaking of rocks into smaller pieces?

Mechanical weathering (correct)

Chemical weathering

Erosion

Mass wasting

What happens during the frost wedging process?

Rocks dissolve in acid rainwater

Rocks are pushed upwards by roots

Water evaporates from rocks causing cracks

Water expands as it freezes, breaking the rock (correct)

How does mass wasting occur?

Through the transfer of rock material downslope by gravity Signup and view all the answers

Why is weathering important for erosion and mass wasting?

It breaks down rocks, making them mobile Signup and view all the answers

What is the main outcome of mechanical weathering?

Increases the surface area of rocks for chemical weathering Signup and view all the answers

What is the process called when indigenous rock dries in layers and exfoliation occurs?

Exfoliation domes Signup and view all the answers

Which of the following materials can undergo weathering?

All types of materials Signup and view all the answers

What is the final result of the decay of plants and animals referred to as?

Humus Signup and view all the answers

How do microorganisms contribute to soil fertility?

By converting nitrogen gas into soil nitrogen compounds Signup and view all the answers

What feature of steep slopes inhibits the development of soil?

Inadequate water infiltration Signup and view all the answers

Which soil type is characterized by an accumulation of iron oxides and aluminum-rich clays?

Pedalfer Signup and view all the answers

What is the term used for the process where fine particles are carried away by water from a soil layer?

Eluviation Signup and view all the answers

Which type of soil typically forms in hot, wet tropical climates under intense chemical weathering?

Laterites Signup and view all the answers

What is a major consequence of removing natural vegetation in an area?

Decreased soil fertility Signup and view all the answers

What happens during sheet erosion?

Soil particles are dislodged by raindrops and flow away in thin layers Signup and view all the answers

Which layer is formed by the accumulation of clay under extreme conditions?

Hardpan Signup and view all the answers

What is the primary characteristic of pedocal soils?

Accumulation of calcium carbonate Signup and view all the answers

What is created when rills enlarge and become deeper?

Gullies Signup and view all the answers

What do dark-colored, thick soils typically indicate?

High levels of organic material and water accumulation Signup and view all the answers

What effect does the orientation of a slope have on soil development?

Orientation impacts sunlight exposure and moisture retention in the soil Signup and view all the answers

What typically accelerates soil erosion rates today compared to the past?

Human activities such as farming and construction Signup and view all the answers

What is the primary role of humus in soil?

To retain nutrients and water Signup and view all the answers

Which of the following best describes the term 'soil texture'?

The proportions of different particle sizes in soil Signup and view all the answers

What term describes the fractures in rock produced by contraction during crystallization and tectonic forces?

Joints Signup and view all the answers

What are 'peds' in soil science?

Clumps formed by soil particles Signup and view all the answers

Which of the following is the primary agent of chemical weathering?

Carbonic acid Signup and view all the answers

How do different sizes of soil particles affect water retention?

Large particles can drain water too quickly Signup and view all the answers

What type of weathering occurs when rocks take on more sphere-like shapes due to water infiltration?

Spheroidal weathering Signup and view all the answers

How do human activities influence weathering processes?

They can lead to acid rain, affecting chemical processes. Signup and view all the answers

Which factor has the strongest influence on soil formation?

Climate Signup and view all the answers

What are residual soils derived from?

Weathered bedrock Signup and view all the answers

Which mineral is noted for its high resistance to chemical weathering?

Quartz Signup and view all the answers

How does precipitation influence soil?

It affects soil fertility and weathering processes Signup and view all the answers

What is the primary composition of soil?

Mineral fragments, organic matter, water, and air Signup and view all the answers

Which statement about organic matter in soil is true?

It is crucial for nutrient supply despite being a small percentage. Signup and view all the answers

Which of the following factors primarily influences the rate of chemical weathering?

Temperature and moisture Signup and view all the answers

What is defined as a common boundary where different Earth systems interact?

Soil Signup and view all the answers

What role does time play in the process of soil formation?

It increases the thickness of soil layers over time. Signup and view all the answers

What is the significance of soil permeability?

It influences how easily air and water move through soil. Signup and view all the answers

Which types of ions are soluble when silicate minerals undergo chemical weathering?

Sodium, calcium, potassium, and magnesium Signup and view all the answers

Which process leads to the alteration of minerals by removing or adding elements?

Chemical weathering Signup and view all the answers

Which of the following best describes 'transported soils'?

Soils formed from unconsolidated deposits brought from elsewhere Signup and view all the answers

In which type of climate would you most likely find thick, chemically weathered soils?

Hot and humid climate Signup and view all the answers

What impact does differential weathering have on rock formations?

It leads to unique and varied geological structures. Signup and view all the answers

What happens to soil characteristics as it ages?

It may develop a thicker profile and change characteristics from its parent material. Signup and view all the answers

What is one consequence of weathering that contributes to soil formation?

Creation of organic matter Signup and view all the answers

Which factor is less significant in determining soil fertility?

The amount of time the soil has existed Signup and view all the answers

In which environment is chemical weathering most ineffective?

Polar regions Signup and view all the answers

What characterizes sheeting in weathering?

It involves unloading of rocks without chemical change Signup and view all the answers

What happens to potassium ions during the weathering of granite?

They are replaced by hydrogen ions. Signup and view all the answers

What is the primary factor that affects the rates of soil erosion in different regions?

The characteristics of the soil and environmental factors Signup and view all the answers

Why is wind erosion considered less significant compared to erosion by flowing water?

Wind erosion typically requires prolonged droughts to be impactful Signup and view all the answers

What consequence arises from the deposition of eroded soil into reservoirs?

Reduced usefulness for water supply and hydroelectric power Signup and view all the answers

What percentage of the world's croplands is estimated to have topsoil eroding faster than it forms?

33% Signup and view all the answers

In what climate does the formation of bauxite typically occur?

Rainy tropical climates Signup and view all the answers

What percentage of soil erosion can be attributed to human activity, according to global studies?

More than 2.5 times the natural rate before humans appeared Signup and view all the answers

Which of the following best describes secondary enrichment in weathering processes?

Desirable elements become concentrated through selective removal Signup and view all the answers

What is the main impact of soil erosion when it exceeds the rate of soil formation?

Reduction in crop quality and agricultural income Signup and view all the answers

What role does leaching play in the formation of bauxite?

It removes soluble impurities from aluminum-rich parent material Signup and view all the answers

What is true about soil conservation methods?

They can significantly reduce soil loss Signup and view all the answers

Study Notes

External Processes

External processes—weathering, mass wasting, and erosion—occur near Earth's surface.
Driven by solar energy.
Weathering: Disintegration and decomposition of rock at or near Earth's surface.
Mass wasting: Transfer of rock material downslope due to gravity.
Erosion: Incorporation and transportation of material by a mobile agent (water, wind, ice).

Weathering

Weathering is intertwined with erosion and mass wasting, as broken rock is moved.
All materials are susceptible to weathering (e.g., concrete).
Causes: Rocks respond to environmental changes. New surface rocks experience new conditions, altering them over time.
Types: Mechanical and chemical.

Mechanical Weathering

Physically breaks rock into smaller pieces.
Increases surface area available for chemical weathering.
Processes:
- Frost wedging: Water expands by 9% when freezing, widening cracks in rocks.
- Expansion from unloading (sheeting): Exfoliation domes form as outer rock layers expand more than the inner ones, separating and breaking off. (unloading= pressure-release)
- Biological activity: Plant roots, burrowing animals, and human activities can break apart rocks.

Chemical Weathering

Alters internal mineral structures by adding or removing elements.
Agents:
- Water and carbonic acid: Essential for chemical weathering; pure water is non-reactive but can dissolve and activate materials. Dissolved oxygen oxidizes materials (rust), while CO2 dissolves to create carbonic acid.
Granite weathering: Hydrogen ions replace potassium ions in feldspar, creating clay minerals, silica, and potassium bicarbonate; quartz is highly resistant and remains largely unchanged.
Silicate mineral weathering: Weathering of common silicate minerals releases soluble ions (sodium, calcium, potassium, magnesium) into groundwater and leaves residual clay minerals resistant to transport.
- Spheroidal weathering: Water attacks corners of rocks more than flat surfaces, leading to more rounded shapes. Weathering from within creates internal forces that cause outer layers of rocks to break off.

Rates of Weathering

Factors Affecting Rates:
- Mineral makeup: Some minerals (e.g., quartz) resist weathering better than others (e.g., marble).
- Climate: Temperature and moisture strongly influence weathering; hot, wet climates favor chemical weathering; cold, dry climates favor mechanical weathering. Human activities (acid rain) also play a role.
Differential weathering: Uneven weathering rates create unique landforms due to differences in mineral composition or exposure.

Soil

Soil covers much of Earth's land surface and plays a vital role in the biosphere and supporting plant life.
Soil is more than weathered rock; it's a combination of mineral fragments, organic matter, air, and water.
Soil is an interface where Earth systems interact.
Soil Components:
- ½ volume = mineral matter and humus (decayed organic matter).
- Air and water fill pore spaces between soil particles. Water contains dissolved nutrients.
Soil Texture & Structure:
- Proportions of different particle sizes (sand, silt, clay) influence water and air retention.
- Clumps of soil particles (peds) create soil structure influencing farming.
Soil Formation Controls:
- Parent material: Bedrock or unconsolidated deposits.
- Time: Longer weathering leads to thicker soil and less resemblance to parent material.
- Climate: Temperature and precipitation control weathering type, depth, and rate.
- Plants and animals: Organic matter from plants and decay contribute nutrients; animals mix soil.
- Slope: Steeper slopes have less well-developed soil, while poorly drained slopes have thick, dark soil.

Soil Profile

Soil forms layers (horizons) as weathering progresses from top-down.
- Eluviation: Movement of finer soil particles downwards by water.
- Leaching: Dissolved inorganic materials carried downwards.
- Zone of accumulation: Materials accumulate, sometimes forming impermeable layers (hardpan).
Solum (true soil): Layers of soil above hardpan showing little resemblance to parent material.

Soil Types

Pedalfers: Iron oxides and aluminum clays accumulate in humid temperate climates.
Pedocals: Calcium carbonate accumulates in temperate dry climates.
Laterites: Intense chemical weathering in hot wet tropical climates; high iron and aluminum oxide concentrations.

Soil Erosion

Natural soil erosion happens, but human activities (farming, construction) accelerate it.
Causes: Raindrop impact, sheet erosion, rills, and gullies.
Measuring: Sediment load in streams and rivers; wind erosion harder to measure.
Rates: Erosion rates exceed formation rates over vast areas, especially in croplands. This issue leads to lower productivity, poor quality crops, lower incomes, and a more precarious agricultural future.

Sedimentation & Chemical Pollution

Excessive erosion leads to sediment deposition in water bodies.
Reduced reservoir capacity, navigation issues, and costly dredging.

Weathering and Ore Deposits

Weathering can concentrate metal ores, a phenomenon called secondary enrichment.
Methods: Some metals are enriched in the upper soil layers, and others are concentrated in lower soil horizons due to leaching.

Bauxite

An aluminum ore formed in rainy tropical climates, due to leaching of most other elements.

Other Deposits

Processes similar to bauxite formation occur to create deposits of other metals.

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Description

Explore the fundamental concepts of weathering, mass wasting, and erosion in this quiz. Learn how these external processes shape the Earth's surface through solar energy. Understand the differences between mechanical and chemical weathering and the mechanisms involved.