Geography Class 17
Exogenic Movements:
- These are the earth's movements caused due to various forces acting from outside the earth's surface.
- The source of energy for these movements are sunlight and gravity.
- Different agents of exogenic movements are wind, river, groundwater, waves, and glaciers.
- Exogenic processes involve aggradation and degradation.
- Aggradation is the action of various processes that cause deposition on the surface to bring uniformity of grade i.e. slope.
- Degradation or denudation involves the combined action of various processes that cause the wearing away of the earth's surface and results in general lowering and levelling out of the earth's surface.
- So, degradation involves weathering, erosion, and mass movements.
Weathering
- It is the total effect of various processes that cooperate in bringing about the decay and disintegration of rocks involving no large-scale transportation.
- Factors affecting weathering:
- 1. Rock type and structure:
- It includes characteristics like origin, massiveness, porosity, permeability, presence of fractures, etc.
- For example, sedimentary rocks are weathered faster than igneous rocks.
- 2. Slope and aspects:
- Steep slopes will greatly add weathering as disintegrated material gets removed faster.
- The slopes which are exposed to wind, rainfall, and sunlight are more prone to weathering.
- E.g. south-facing slopes of the Himalayas.
- 3. Temperature:
- The range of temperature, particularly the diurnal range subjects the surface layer to expansion and contraction continuously causing a physical breakdown.
- Temperature also increases the rate of certain chemical reactions.
- 4. Water:
- When water is added or removed, it imposes mechanical stress on the rocks and causes them to split.
- Water also decides the rate of chemical reactions.
- 5. Biological agents:
- These include the action of plant roots, micro-organisms, and burrowing animals.
Types of weathering
- Difference between Mechanical and Chemical weathering:
Mechanical (Physical) Weathering Chemical Weathering The disintegration of rocks takes place without any change in the chemical constituents of the rocks The disintegration of rocks takes place with changes in the chemical constituents of the rocks Factors such as temperature, moisture, frost action, and wind cause the physical breakup of the rocks. Temperature, moisture, etc. cause minerals in the rocks to either dissolve in water or change their composition It is more rapid in desert climates It occurs in moist and cool climates Rocks are effect to great depth It mostly takes place near the surface of the earth Its agents are temperature and moisture Its agents are water, oxygen, carbon, and various organic acids - Physical weathering:
- Crystal growth
- Growth of water crystal: When water freezes it expands and finds its way into cracks or pores, it wedges apart rock fissures and joints. In desert regions, it results in frost shattering, in glacial regions it causes freeze-thaw.
- Salt crystal: Growth of salt crystal by crystallization as moisture evaporates creating pressure in pore spaces and cracks. It is also called Haloclasty (salt weathering).
- Pressure or thermal expansion:
- 1. Exfoliation: Rapid expansion and contraction of surface rocks weaken the outer shell creating cracks and causing the rock shell to peel off
- 2. Pressure release: Confining pressed from the weight of overlying rocks is released, when the upper layer of rocks is removed by degradation. This causes rocks to expand leading to the development of fractures.
- 3. Block disintegration: Here weathering causes the breakdown of rocks in blocks.
- 4. Granular disintegration: Here breakdown occurs in granules.
- Chemical Weathering:
- Hydrolysis:
- It is the chemical union of water and minerals.
- It produces solutions.
- Hydration:
- It is when minerals incorporate water into their molecular structure.
- It causes swelling.
- Oxidation and Reduction:
- It involves the addition or removal of oxygen.
- It causes discolouration. E.g. rusting of iron.
- They are the first visible sign of chemical weathering.
- Carbonation:
- Rainwater absorbs carbon dioxide and gets converted into carbonic acid.
- Limestone and dolomites are altered by the dissolving action of carbonic acid.
- Biological Weathering
- It is a type of weathering due to the action of biological agents.
Erosion:
- Erosion refers to the wearing away of the land surface by the mechanical action of debris derived from weathering as they are transported to a different location by agents of wind, water, glacier, etc.
- Types of Erosion:
- Abrasion:
- Wearing away surfaces by mechanical processes such as rubbing, scratching, polishing, etc.
- Abrasion in water is called corrasion.
- Attrition:
- It involves the reduction in the size of fragments by friction and impact during transportation.
- It breaks down the load into finer sediments.
- Cavitation:
- The collapse of water bubbles in rivers leads to an explosion sending a shock wave that tends to disintegrate the adjacent rocks which are cavitation.
- Corrosion:
- It involves the breaking of rocks by the solvent and the chemical action of water.
- Deflation:
- The lifting and removal of dust and sand by wind are called deflation.
- Hydraulic action:
- Breaking of rocks by fast-moving water.
- Plucking:
- As the glacier moves, they drag the rocks and disintegrate them into smaller pieces.
Mass Movement:
- The weathered material moving downhill slopes under the influence of gravity with or without the assistance of running water is called a mass movement.
- It is a large-scale breakdown or disintegration.
- It is also called mass wasting.
Topics for the next class: Types of mass movements, and different types of landforms.
What are exogenic movements?
- Earth's movements caused by forces acting from outside the earth's surface.
What is the source of energy for exogenic movements?
- Sunlight and gravity.
Name the different agents of exogenic movements.
- Wind, river, groundwater, waves, and glaciers.
What does aggradation involve in exogenic processes?
- Deposition on the surface to bring uniformity of grade or slope.
What does degradation or denudation involve?
- The wearing away of the earth's surface, resulting in the general lowering and leveling out of the earth's surface.
What processes are included in degradation?
- Weathering, erosion, and mass movements.
What is weathering?
- The total effect of processes that cause the decay and disintegration of rocks without large-scale transportation.
How does rock type and structure affect weathering?
- Characteristics like origin, massiveness, porosity, permeability, and presence of fractures affect the rate of weathering.
Give an example of rock type affecting weathering.
- Sedimentary rocks weather faster than igneous rocks.
How does slope and aspect affect weathering?
- Steep slopes increase weathering as disintegrated material is removed faster; slopes exposed to wind, rainfall, and sunlight are more prone to weathering.
How does temperature affect weathering?
- Temperature variations cause physical breakdown and increase the rate of certain chemical reactions.
How does water contribute to weathering?
- Water causes mechanical stress and influences the rate of chemical reactions in rocks.
What are biological agents of weathering?
- Plant roots, microorganisms, and burrowing animals.
What is mechanical (physical) weathering?
- Disintegration of rocks without changing their chemical constituents.
What is chemical weathering?
- Disintegration of rocks with changes in their chemical constituents.
Which climates favor physical weathering?
- Desert climates.
Which climates favor chemical weathering?
- Moist and cool climates.
What causes physical weathering?
- Factors like temperature, moisture, frost action, and wind.
What are the agents of chemical weathering?
- Water, oxygen, carbon, and various organic acids.
What is crystal growth in physical weathering?
- Growth of water or salt crystals that cause rocks to break apart.
What is exfoliation in physical weathering?
- Rapid expansion and contraction of surface rocks causing them to peel off.
What is pressure release in physical weathering?
- Rocks expand and develop fractures as overlying rocks are removed by degradation.
What is block disintegration in physical weathering?
- Weathering causes the breakdown of rocks into blocks.
What is granular disintegration in physical weathering?
- Weathering causes the breakdown of rocks into granules.
What is hydrolysis in chemical weathering?
- Chemical union of water and minerals producing solutions.
What is hydration in chemical weathering?
- Incorporation of water into minerals causing them to swell.
What is oxidation and reduction in chemical weathering?
- Addition or removal of oxygen causing discoloration, such as rusting of iron.
What is carbonation in chemical weathering?
- Rainwater absorbs carbon dioxide and forms carbonic acid, which dissolves limestone and dolomites.
What is biological weathering?
- Weathering due to the action of biological agents.
What is erosion?
- Wearing away of the land surface by mechanical action of debris transported by wind, water, glacier, etc.
What is abrasion in erosion?
- Wearing away surfaces by rubbing, scratching, polishing, etc.
What is attrition in erosion?
- Reduction in the size of fragments by friction and impact during transportation.
What is cavitation in erosion?
- Collapse of water bubbles causing shock waves that disintegrate adjacent rocks.
What is corrosion in erosion?
- Breaking of rocks by the solvent and chemical action of water.
What is deflation in erosion?
- Lifting and removal of dust and sand by wind.
What is hydraulic action in erosion?
- Breaking of rocks by fast-moving water.
What is plucking in erosion?
- Glaciers drag rocks and disintegrate them into smaller pieces.
What is mass movement?
- Downhill movement of weathered material under the influence of gravity, also called mass wasting.
What are the key processes involved in mass movement?
- Large-scale breakdown or disintegration of weathered material.
What topics will be covered in the next class?
- Types of mass movements and different types of landforms.
1.
Explain the concept of exogenic movements and discuss the role of various
agents involved in these processes.
Answer:
Exogenic
movements are processes that occur due to forces acting from outside the
Earth's surface, primarily driven by sunlight and gravity. These movements
include various activities such as weathering, erosion, transportation, and
deposition, which collectively shape the Earth's landscape. The primary agents
of exogenic movements are wind, rivers, groundwater, waves, and glaciers.
Role of
Various Agents:
- Wind: Wind causes erosion,
transportation, and deposition of materials, especially in arid and
semi-arid regions. It can create landforms such as dunes and loess
deposits through its ability to transport fine particles over long
distances.
- Rivers: Rivers play a crucial role
in shaping landscapes through erosion, transportation, and deposition.
They carve valleys, create floodplains, and form deltas as they deposit
sediments at their mouths.
- Groundwater: Groundwater contributes to
weathering and erosion by dissolving soluble minerals, leading to the
formation of features like caves and sinkholes through a process known as
chemical weathering.
- Waves: Waves erode coastlines
through hydraulic action, abrasion, and corrosion. They transport and
deposit sediments, forming features such as beaches, spits, and barrier
islands.
- Glaciers: Glaciers erode the
landscape by plucking and abrasion as they move. They transport debris and
deposit it as till, creating landforms like moraines, drumlins, and
eskers.
Exogenic
processes are categorized into aggradation and degradation:
- Aggradation: This process involves the
deposition of materials, leading to the build-up and elevation of the
Earth's surface. It aims to bring uniformity to the slope of the land.
- Degradation (Denudation): This involves the wearing
away of the Earth's surface through weathering, erosion, and mass
movements, resulting in the lowering and leveling of the surface.
By
understanding these processes and agents, we can better appreciate the dynamic
nature of the Earth's surface and the continuous cycle of material being worn
down and built up.
2.
Discuss the factors affecting weathering and how different rock types respond
to weathering processes.
Answer:
Weathering
is the process by which rocks are broken down into smaller pieces through
physical, chemical, and biological mechanisms. Several factors influence the
rate and extent of weathering:
Factors
Affecting Weathering:
- Rock Type and Structure:
- The origin, massiveness,
porosity, permeability, and presence of fractures determine how rocks
weather. For instance, sedimentary rocks, being more porous and less
compact, weather faster than igneous rocks.
- Slope and Aspects:
- Steep slopes enhance
weathering because disintegrated materials are quickly removed, exposing
fresh surfaces. Slopes exposed to wind, rainfall, and sunlight experience
more intense weathering, as seen in the south-facing slopes of the
Himalayas.
- Temperature:
- Temperature fluctuations
cause expansion and contraction of the surface layer, leading to physical
breakdown. Higher temperatures also accelerate chemical reactions,
contributing to chemical weathering.
- Water:
- Water can cause mechanical
stress on rocks by adding or removing moisture, leading to splitting. It
also drives chemical reactions, influencing the rate of chemical
weathering.
- Biological Agents:
- Plant roots,
microorganisms, and burrowing animals contribute to biological weathering
by breaking down rocks through physical and chemical means.
Responses
of Different Rock Types to Weathering:
- Sedimentary Rocks: These rocks, being more
porous and often containing minerals that dissolve easily, are more
susceptible to both mechanical and chemical weathering. For example,
limestone is prone to chemical weathering through carbonation.
- Igneous Rocks: These rocks are generally
more resistant to weathering due to their dense and compact nature.
However, they can still be affected by mechanical weathering through
temperature fluctuations and physical forces.
- Metamorphic Rocks: These rocks are also
relatively resistant to weathering but can be weathered chemically if they
contain minerals that react with water or atmospheric gases.
Understanding
the factors affecting weathering helps in predicting the durability of
different rock types and their behavior in various environmental conditions.
3.
Compare and contrast mechanical and chemical weathering, providing examples of
each type.
Answer:
Mechanical
(Physical) Weathering and Chemical Weathering are two primary types of
weathering processes that break down rocks through different mechanisms:
Mechanical
Weathering:
- Definition: The disintegration of
rocks without any change in their chemical composition.
- Agents: Temperature, moisture,
frost action, and wind.
- Processes:
- Crystal Growth: Water freezing in cracks
expands, causing rocks to split. This is known as frost shattering in
deserts and freeze-thaw in glacial regions.
- Salt Crystal Growth: Salt crystals form as
moisture evaporates, exerting pressure in pore spaces and cracks, a
process called Haloclasty.
- Exfoliation: Rapid expansion and
contraction due to temperature changes cause the outer rock layer to peel
off.
- Pressure Release: Rocks expand and develop
fractures when the overlying material is removed.
- Block and Granular
Disintegration: Rocks
break down into blocks or granules due to mechanical stress.
Chemical
Weathering:
- Definition: The disintegration of
rocks involving changes in their chemical composition.
- Agents: Water, oxygen, carbon
dioxide, and organic acids.
- Processes:
- Hydrolysis: Chemical union of water
and minerals, producing solutions.
- Hydration: Minerals incorporate
water, causing swelling.
- Oxidation and Reduction: Addition or removal of
oxygen, causing discoloration (e.g., rusting of iron).
- Carbonation: Rainwater absorbs carbon
dioxide, forming carbonic acid that dissolves limestone and dolomites.
Comparison:
- Nature: Mechanical weathering
involves physical breakdown without altering chemical composition, while
chemical weathering changes the chemical constituents of rocks.
- Climate: Mechanical weathering is
rapid in desert climates due to temperature fluctuations, whereas chemical
weathering is prevalent in moist and cool climates.
- Depth: Mechanical weathering can
affect rocks to great depths, while chemical weathering primarily occurs
near the surface.
- Agents: Mechanical weathering is
driven by physical forces such as temperature and moisture, while chemical
weathering involves chemical reactions with water, oxygen, and carbon.
Examples:
- Mechanical Weathering: Frost shattering in
deserts and exfoliation in mountainous regions.
- Chemical Weathering: Rusting of iron
(oxidation) and dissolution of limestone by carbonic acid (carbonation).
Understanding
both types of weathering helps in comprehending how rocks break down and
transform over time, shaping the Earth's surface.
4.
Describe the different types of erosion and their impact on the landscape.
Answer:
Erosion
is the process by which the land surface is worn away by the mechanical action
of agents such as wind, water, glaciers, and gravity. This process involves the
transportation of weathered materials to different locations, reshaping the
landscape.
Types of
Erosion and Their Impact:
- Abrasion:
- Description: Mechanical wearing away
of surfaces by rubbing, scratching, and polishing. In water, this process
is known as corrasion.
- Impact: Creates smooth and
polished surfaces on rocks and bedrock, forming features like riverbeds
and coastal cliffs.
- Attrition:
- Description: Reduction in the size of
rock fragments due to friction and impact during transportation.
- Impact: Breaks down larger rocks
into finer sediments, contributing to the formation of sand and silt in
riverbeds and coastal areas.
- Cavitation:
- Description: Collapse of water bubbles
in rivers, leading to explosive shock waves that disintegrate adjacent
rocks.
- Impact: Creates potholes and
deepens river channels, contributing to the sculpting of river
landscapes.
- Corrosion:
- Description: Chemical breakdown of
rocks by the solvent action of water.
- Impact: Dissolves minerals,
leading to the formation of features like limestone caves and karst
topography.
- Deflation:
- Description: Lifting and removal of
dust and sand by wind.
- Impact: Creates desert pavements,
deflation hollows, and dunes, significantly altering arid landscapes.
- Hydraulic Action:
- Description: Breaking of rocks by the
force of fast-moving water.
- Impact: Erodes riverbanks and
coastal cliffs, forming features such as waterfalls and wave-cut
platforms.
- Plucking:
- Description: Glacier movement dragging
rocks and disintegrating them into smaller pieces.
- Impact: Creates jagged landscapes
with features like glacial valleys, cirques, and fjords.
Impact on
the Landscape: Erosion
plays a crucial role in shaping the Earth's surface by wearing down mountains,
creating valleys, and forming sedimentary basins. It redistributes materials,
leading to the creation of various landforms such as river deltas, coastal
beaches, and desert dunes. Erosion also influences soil formation and fertility
by transporting nutrients. However, excessive erosion can lead to land
degradation, loss of fertile soil, and increased sedimentation in water bodies,
affecting ecosystems and human activities.
Understanding
the different types of erosion and their impacts helps in managing land use and
mitigating the adverse effects of soil erosion on the environment and
agriculture.
5.
Explain the concept of mass movement and describe the various types of mass
wasting processes.
Answer:
Mass
movement, also known as mass wasting, refers to the downhill movement of weathered
material under the influence of gravity, with or without the assistance of
running water. This process involves the large-scale breakdown or
disintegration of materials from slopes.
Concept
of Mass Movement:
- Gravity-Driven: Mass movement is primarily
driven by gravitational forces acting on weathered materials, causing them
to move downhill.
- Types of Material: The material involved in
mass movement can range from loose soil and rock debris to large boulders
and entire sections of the hillside.
- Water's Role: Water can act as a
lubricant, reducing friction and making it easier for materials to slide
or flow downhill.
Types of
Mass Wasting Processes:
- Creep:
- Description: Slow, gradual downhill
movement of soil and rock debris.
- Impact: Causes bent trees, tilted
fences, and distorted roads over long periods.
- Slump:
- Description: Downward and outward
movement of a mass of rock or soil along a curved surface.
- Impact: Forms steep scarps and
terraces, commonly occurring on slopes with clay-rich soils.
- Rockfall:
- Description: Rapid free-fall of rock
from a steep slope or cliff.
- Impact: Accumulates talus or
scree at the base of the slope, posing hazards to roads and
infrastructure.
- Landslide:
- Description: Sudden and rapid movement
of a large mass of earth material down a slope.
- Impact: Causes significant damage
to structures, roads, and vegetation in its path.
- Mudflow:
- Description: Rapid flow of
water-saturated earth material, often occurring in arid regions after
heavy rainfall.
- Impact: Transports large amounts
of debris, depositing it over extensive areas, and can cause severe
damage to settlements.
- Earthflow:
- Description: Slow to rapid flow of
saturated earth material down a slope.
- Impact: Forms tongue-shaped lobes
of debris, often occurring in clay-rich soils.
- Debris Flow:
- Description: Rapid flow of a mixture
of water, soil, rock, and organic matter.
- Impact: Highly destructive,
capable of carrying large boulders and uprooting trees, often triggered
by heavy rainfall or volcanic activity.
Impact of
Mass Movement: Mass
movements significantly alter landscapes by reshaping slopes, creating new
landforms, and transporting materials to lower elevations. While they play a
natural role in landscape evolution, they can also pose hazards to human
activities and infrastructure. Understanding mass movement processes is crucial
for risk assessment, land-use planning, and implementing mitigation measures to
reduce the impact of landslides and other mass wasting events.
By
studying the types and causes of mass movements, we can develop strategies to
prevent or minimize the damage caused by these natural processes, ensuring
safer and more sustainable land management practices.
1)
With reference to Weathering, consider the following statements:
- Rocks of different compositions weather at different rates.
- Increasing organic activity increases the rate of weathering.
- Weathering is an in-situ process and does not involve the transportation of degraded rock materials.
Which of the statements given above is/are correct?
(a)1 only
(b)2 and 3 only
(c)1 and 2 only
(d)1, 2 and 3
2)
Consider the following statements:
1. Erosion is the breakdown of rocks in movement.
2. Mass movement is the in-situ breakdown of rocks.
3. Weathering happens under the influence of gravity.
How many of the above statements is/are correct?
(a)One only
(b)Two only
(c)All of the above
(d)None of the above
3)
Consider the following statements:
- The actions of exogenic forces result in the wearing down (degradation) of relief/elevations and filling up (aggradation) of basins/depressions, on the earth’s surface.
- The exogenic geomorphic processes vary from region to region.
Which of the above statement(s) is/are incorrect:
(a)1 only
(b)2 only
(c)Both 1 and 2
(d)Neither 1 nor 2
4)
Consider the following statements concerning biological weathering:
- Burrowing and digging of animals such as rabbits and rodents result in weathering.
- Plant or tree root system breaks the rocks resulting in weathering.
- Humans mostly increase the rate of weathering through anthropogenic actions such as construction, agriculture, mining, changing land use patterns, deforestation, etc.
Which of the given statement is/are not correct?
(a)1 and 2 only.
(b)2 and 3 only.
(c)1 and 3 only.
(d)None of the above.
5)
Consider the following statements:
- All the endogenic forces are constructive forces.
- All the exogenic forces are levelling forces.
- Both the endogenic and exogenic processes happen simultaneously.
Which of the statements given above is/are correct?
(a)1 and 2 only
(b)2 and 3 only
(c)1 and 3 only
(d)1, 2 and 3
6)
Consider the following pairs:
Types of erosion: Agent:
Cavitation Corrosive water action
Deflation Collapsing water bubbles
Hydraulic action Fast moving water
Plucking Wind
How many pairs given above are correctly matched?
(a)Only one pair
(b)Only two pairs
(c)Only three pairs
(d)All four pairs
7)
Which of the following statements regarding hydration is/are not correct?
- It is the process of incorporating water molecules into the molecular structure of minerals.
- It is a type of physical weathering.
- It leads to the growth of water crystals, which wedges apart rock fissures and joints.
(a)1 and 2
(b)2 and 3
(c)1
(d)1, 2 and 3
8)
Consider the following statements:
- Haloclasty is weathering due to salt crystals.
- Abrasion in water is called corassion.
- Hydrolysis is the absorption of water molecules by minerals.
- Carbonation is the action of carbonic acid upon rocks.
(a)Only one statement is correct.
(b)Only two statements are correct
(c)Only three statements are correct.
(d)All statements are correct.
9)
How is physical weathering different from chemical weathering? Explain with examples. (10 marks/ 150 words)
10)
What are exogenic movements? Discuss the factors affecting weathering process. (10 marks / 150 marks)
Answers
1) d
2) a
3) d
4) d
5) d
6) a
7) b
8) c
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