5.1 Physical and chemical weathering processes
2 min read•july 24, 2024
Rocks break down over time through physical and . splits rocks into smaller pieces, while chemical weathering changes their makeup. These processes work together, with physical weathering exposing more rock to chemical reactions.
Water plays a huge role in both types of weathering. It freezes in cracks to split rocks, carries particles that wear down surfaces, and reacts chemically with minerals. Temperature, acidity, and dissolved gases all affect how water weathers rocks.
Physical Weathering Processes
Physical vs chemical weathering
Top images from around the web for Physical vs chemical weathering
Putting It Together: Rocks and the Rock Cycle | Geology View original
Is this image relevant?
Rock Weathering CO2 Cycle (with annotations) View original
Is this image relevant?
Introduction | Physical Geology View original
Is this image relevant?
Putting It Together: Rocks and the Rock Cycle | Geology View original
Is this image relevant?
Rock Weathering CO2 Cycle (with annotations) View original
Is this image relevant?
1 of 3
Top images from around the web for Physical vs chemical weathering
Putting It Together: Rocks and the Rock Cycle | Geology View original
Is this image relevant?
Rock Weathering CO2 Cycle (with annotations) View original
Is this image relevant?
Introduction | Physical Geology View original
Is this image relevant?
Putting It Together: Rocks and the Rock Cycle | Geology View original
Is this image relevant?
Rock Weathering CO2 Cycle (with annotations) View original
Is this image relevant?
1 of 3
- Physical weathering mechanically breaks down rocks without altering chemical composition creates smaller fragments with identical mineral makeup
- Chemical weathering alters rock minerals through chemical reactions changes composition often produces new minerals or dissolves existing ones
- Physical weathering increases surface area exposed to chemical processes while chemical weathering weakens rock structures making them more susceptible to physical breakdown
Types of physical weathering
- Frost wedging water freezes and expands in rock cracks repeated freeze-thaw cycles fragment rock (mountain slopes)
- curved rock sheets peel away from main body caused by pressure release as overlying rock erodes (Half Dome, Yosemite)
- mechanical wearing of rock surfaces by other particles common in riverbeds, glaciers, and windblown environments (Grand Canyon)
- daily temperature fluctuations cause rock to expand and contract leads to fracturing over time (desert landscapes)
- plant roots grow into rock cracks widening them eventually splitting rocks apart (cliff faces)
Chemical Weathering Processes
Chemical weathering processes
- reaction between water and rock-forming minerals breaks down silicates () produces clay minerals and dissolved ions
- reaction between oxygen and iron-bearing minerals forms iron oxides (rust) common in exposed environments (red rocks)
- reaction between carbonic acid and minerals carbonic acid forms when CO2 dissolves in water effectively dissolves limestone (karst )
- direct dissolving of minerals in water affects highly soluble minerals (halite)
- addition of water molecules to mineral structures causes expansion and rock weakening (gypsum formation)
Water's role in weathering
- Physical weathering:
- Freezes in cracks causing frost wedging
- Transports abrasive particles in rivers and glaciers
- Facilitates plant growth for root wedging
- Chemical weathering:
- Primary reactant in hydrolysis
- Solvent for dissolved CO2 in carbonation
- Medium for ion exchange in various reactions
- Factors affecting water's potential: Temperature influences reaction rates and freeze-thaw cycles pH affects rate and type of chemical weathering Dissolved gases (CO2) enhance chemical processes
- Water cycle impact: Precipitation delivers fresh water to rock surfaces Groundwater movement facilitates subsurface weathering Evaporation concentrates minerals leading to salt weathering (coastal cliffs)
Key Terms to Review (22)
Abrasion: Abrasion is the process of wearing away material from a surface through friction and impact, often caused by the movement of particles. It plays a crucial role in shaping landscapes by removing soil and rock, and contributes to the formation of various geological features over time.
Calcite: Calcite is a carbonate mineral with the chemical formula CaCO₃, known for its prominent role in geological processes and the formation of sedimentary rocks. This mineral forms from both biological processes, such as the accumulation of marine organisms, and chemical precipitation, often resulting from evaporation. Calcite is also significant in understanding weathering processes as it can dissolve in slightly acidic conditions, impacting soil and rock formation.
Carbonation: Carbonation is a chemical weathering process that involves the reaction between carbon dioxide (CO₂) in the atmosphere or soil and water to form carbonic acid (H₂CO₃), which then reacts with minerals in rocks. This process plays a significant role in breaking down limestone and other carbonate rocks, contributing to soil formation and affecting the landscape over time.
Chemical weathering: Chemical weathering is the process by which rocks and minerals undergo chemical alterations due to interactions with water, air, and biological organisms. This type of weathering breaks down the original minerals and forms new minerals, often leading to soil formation and altering landscapes. Understanding chemical weathering is crucial as it contributes to soil development, influences the characteristics of different soil profiles, and plays a significant role in the formation of unique landforms such as karst landscapes.
Climate: Climate refers to the long-term average of weather conditions, including temperature, precipitation, humidity, and wind patterns in a particular region over extended periods, usually 30 years or more. It plays a crucial role in shaping various Earth processes, influencing the rock cycle, soil formation, weathering, erosion, and the hydrologic cycle.
Degradation: Degradation refers to the process by which rocks and minerals break down into smaller particles, leading to the alteration of the landscape and contributing to soil formation. This term is closely tied to both physical and chemical weathering processes, as these mechanisms facilitate the breakdown of materials, allowing for the transport and eventual deposition of sediments. The importance of degradation lies in its role in shaping Earth's surface and influencing ecosystem dynamics.
Dissolution: Dissolution is the process by which solid materials dissolve in a solvent, usually water, resulting in the formation of a solution. This process plays a significant role in both physical and chemical weathering, as well as in the development of unique landforms associated with karst environments. The dissolution of minerals, particularly carbonates like limestone, contributes to shaping the landscape and affects various geological processes.
Exfoliation: Exfoliation is a geological process where rock layers peel or flake off in sheets or slabs due to physical weathering, typically caused by temperature changes and pressure release. This process is significant in shaping landscapes, especially in granite formations, where large masses can break apart and create distinctive landforms. Exfoliation is closely linked to physical weathering processes and can be influenced by various environmental factors that affect the rates of weathering and erosion.
Feldspar: Feldspar is a group of rock-forming minerals that are essential components of many igneous, metamorphic, and sedimentary rocks. This mineral group is characterized by its aluminosilicate structure, consisting primarily of aluminum, silicon, and oxygen, often combined with potassium, sodium, or calcium. Feldspar plays a significant role in the physical and chemical weathering processes of rocks, contributing to soil formation and influencing mineral classification based on their unique properties.
Freeze-thaw weathering: Freeze-thaw weathering is a physical weathering process where water seeps into cracks in rocks, freezes when temperatures drop, and expands, causing the rock to fracture. This cycle repeats as temperatures fluctuate, leading to gradual breakdown of the rock material over time. The process is significant in shaping landscapes and contributes to soil formation by breaking down larger rocks into smaller particles.
Hydration: Hydration is a chemical process in which water molecules are incorporated into the structure of a mineral or compound, causing a change in its physical and chemical properties. This process plays a significant role in weathering, as it can weaken the bonds within minerals, leading to their breakdown and contributing to soil formation and landscape alteration.
Hydrolysis: Hydrolysis is a chemical weathering process that involves the reaction of water with minerals, leading to the breakdown of the mineral structure and the formation of new minerals. This process is crucial in transforming feldspar into clay minerals, significantly altering soil composition and influencing erosion rates. By breaking down silicate minerals, hydrolysis not only contributes to soil formation but also plays a vital role in shaping landscapes and determining the availability of nutrients in the environment.
Landform development: Landform development refers to the processes and mechanisms that shape and alter the Earth's surface features over time. This includes the formation of various landforms such as mountains, valleys, and plateaus due to the combined effects of erosion, deposition, and tectonic activity. Understanding these processes is crucial for comprehending how landscapes evolve and change, and how weathering plays a significant role in this transformation.
Oxidation: Oxidation is a chemical process where a substance loses electrons, often resulting in an increase in oxidation state. This process is crucial in the breakdown of minerals and organic materials, contributing significantly to chemical weathering. Oxidation can change the composition and properties of rocks and soils, leading to their disintegration over time.
Physical Weathering: Physical weathering refers to the mechanical breakdown of rocks and minerals into smaller fragments without altering their chemical composition. This process plays a critical role in soil formation and influences soil profiles by contributing to the mineral content and structure of soils, which are essential for plant growth and ecosystem health.
Regolith: Regolith is a layer of loose, fragmented material that covers solid bedrock, consisting of soil, rock fragments, and other materials. It plays a crucial role in the physical and chemical weathering processes as it forms from the breakdown of rocks and minerals, providing a medium for soil formation and influencing landscape development.
Root wedging: Root wedging is a physical weathering process where plant roots grow into cracks and crevices in rocks, exerting pressure as they expand. This mechanical action can cause the rock to break apart, contributing to soil formation and landscape changes. It's a natural phenomenon that illustrates how living organisms interact with geological materials, highlighting the connection between biological and geological processes.
Soil Horizons: Soil horizons are distinct layers of soil that develop as a result of soil formation processes and are characterized by different physical, chemical, and biological properties. These layers, which include the O, A, E, B, and C horizons, reflect the influence of weathering processes on the parent material and contribute to soil classification and fertility. Understanding soil horizons is crucial for determining land use, agriculture, and environmental management.
Thermal expansion and contraction: Thermal expansion and contraction refer to the tendency of materials to change their dimensions in response to temperature changes, where most materials expand when heated and contract when cooled. This physical property is crucial in understanding various geological processes, as temperature fluctuations can lead to physical weathering, causing rocks and minerals to break down over time due to the stress from these changes.
Topography: Topography refers to the arrangement of the natural and artificial physical features of an area, including its terrain, elevation, and landforms. Understanding topography is essential as it influences geological processes, the formation of soil, weathering, erosion rates, and the movement of water through drainage systems.
Weathering rate: Weathering rate refers to the speed at which rocks and minerals break down due to physical and chemical processes. This breakdown is crucial for soil formation and nutrient cycling, influencing landscape changes over time. Various factors like climate, rock type, and surface area significantly affect how quickly weathering occurs.
Weathering resistance: Weathering resistance refers to the ability of a material, particularly rocks and minerals, to withstand the processes of weathering without significant degradation. This concept is crucial in understanding how different materials respond to physical and chemical weathering processes, which can lead to the breakdown of rocks and minerals over time due to environmental factors such as temperature changes, water, and biological activity.