Questions Answers Class 11 Chapter 2 Geography Maharashtra Board

Weathering and Mass Wasting

Q. 1) Complete the chain :

Answer:

Q. 2) Identify the correct correlation :

A : Assertion; R : Reasoning

1) A : In areas of high rainfall, slides are very common.
R : Types of mass wasting movements are dependent on a region’s climate.

1) Only A is correct
2) Only R is correct
3) Both A and R are correct and R is the correct nexplanation of A.
4) Both A and R are correct but R is not the correct explanation of A.

Answer: 3) Both A and R are correct and R is the correct explanation of A.

• Explanation: The document states that humid climates tend to have slides, indicating that high rainfall increases the likelihood of mass wasting events like slides due to water saturation reducing friction and increasing material weight (p. 23). This supports the assertion (A) that slides are common in high-rainfall areas. The reasoning (R) is also correct, as the document explains that a region’s climate, including rainfall, determines the type and likelihood of mass wasting movements (p. 23). The reasoning directly explains why high rainfall leads to slides, making it the correct explanation of the assertion.

2) A : Gravity is a major factor in mass wasting.
R : Gravity pulls all things down to the earth’s surface.

1) Only A is correct
2) Only R is correct
3) Both A and R are correct and R is the correct explanation of A.
4) Both A and R are correct but R is not the correct explanation of A.

Answer: 3) Both A and R are correct and R is the correct explanation of A.

• Explanation: The document states that gravity is the main force responsible for mass movements, pulling everything down the Earth’s surface (p. 22). This directly supports the assertion that gravity is a major factor in mass wasting, and the reasoning explains why gravity causes this movement.

3) A : Freeze and thaw weathering is common in desert areas.
R : Water gets into cracks and breaks the rocks.
1) Only A is correct
2) Only R is correct
3) Both A and R are correct and R is the correct explanation of A.
4) Both A and R are correct but R is not the correct explanation of A.

Answer: 2) Only R is correct.

• Explanation: The document explains that freeze-and-thaw weathering occurs when water in cracks freezes and expands, breaking rocks (p. 16). However, it specifies that this process is effective in high altitudes, mid and low latitudes, high-latitudes, and mountainous regions, not desert areas where water availability is rare (p. 17). Thus, the assertion is incorrect, but the reasoning is correct.

4) A : Surface water helps solifluction
R : Water table is responsible for the same.
1) Only A is correct
2) Only R is correct
3) Both A and R are correct and R is the correct explanation of A.
4) Both A and R are correct but R is not the correct explanation of A.

Answer: 4) Both A and R are correct but R is not the correct explanation of A.

• Explanation: The document describes solifluction as the slow downhill creep of soil in periglacial or alpine regions, where soil overlying permafrost becomes oversaturated and slides due to gravity (p. 24). Surface water contributes to this saturation, supporting the assertion. The water table, related to permafrost impermeability, is also involved, but it is not the direct cause of solifluction, making the reasoning correct but not the primary explanation.

Q. 3) Identify the correct group :

A) 1) Oxidation 2) Carbonation 3) Freeze-thaw weathering 4) Shattering

Answer: Incorrect.

• Explanation: Oxidation and carbonation are chemical weathering processes (p. 16), but freeze-thaw weathering and shattering are physical weathering processes (p. 16-17). This group mixes types of weathering, so it is not correct.

B) 1) Solution 2) Salt Weathering 3) Oxidation 4) Carbonation

Answer: Incorrect.

• Explanation: Solution, oxidation, and carbonation are chemical weathering processes (p. 16), but salt weathering is a physical weathering process (p. 17). This group also mixes types, so it is not correct.

C) 1) Fall 2) Creep 3) Slide 4) Flow

Answer: Correct.

• Explanation: Fall, creep, slide, and flow are all types of mass wasting movements as classified in the document (p. 23-24). They are correctly grouped together as they all describe mass wasting processes based on speed and material movement.

D) 1) Pressure 2) Temperature 3) Slope 4) Rainfall

Answer: Incorrect.

• Explanation: While pressure, temperature, slope, and rainfall are factors affecting weathering and mass wasting (p. 17-18, 22), they are not a uniform group of processes or types like the options in A, B, or C. They are contributing factors, not a cohesive category.

Correct Group: C) 1) Fall 2) Creep 3) Slide 4) Flow

Q. 4) Give geographical reasons :

1) Temperature is the main factor behind granular weathering.

Answer: In areas with high diurnal temperature ranges, such as hot deserts, rocks are subjected to differential thermal expansion and contraction. Minerals in the rock expand and contract at different rates due to temperature changes, creating stresses that cause individual mineral grains to break free, leading to granular weathering (p. 17, Fig. 2.5).

2) Human is an agent of weathering.

Answer: Human activities like mining, blasting for construction, quarrying, and deforestation accelerate rock disintegration. These actions, termed anthropogenic weathering, disrupt rock structures and expose them to weathering processes, achieving in a short time what natural weathering might take thousands to millions of years (p. 19).

3) Slope is a major factor in mass wasting.

Answer: Steeper slopes increase the likelihood and speed of mass wasting because gravity pulls materials downward more effectively. The document notes that hilly, mountainous, and plateau areas with considerable elevation are more vulnerable, with steeper slopes leading to rapid movements compared to gentle slopes (p. 22).

4) Oxidation changes the size and colour of the rocks.

Answer: Oxidation occurs when oxygen reacts with minerals like iron and aluminum in rocks, forming oxides. These oxides are less hard, larger in volume, and have distinct colors (e.g., red for iron oxides, yellow for aluminum oxides), altering both the size and color of the rock (p. 16, Fig. 2.3).

5) Effect of mass movement will be greater along the western slope of the Sahyadris than the eastern slope.

Answer: The western slopes of the Sahyadris receive heavier rainfall due to the orographic effect of the monsoon, leading to increased water saturation of soils and reduced friction. This, combined with steeper slopes and potential vegetation loss, makes mass movements like landslides more frequent and severe compared to the drier, gentler eastern slopes (inferred from p. 21-23, discussing water and slope impacts).

Q. 5) Write short notes on :

1) Gravity and Solifluction

Answer: Gravity is the primary force driving solifluction, a slow downhill creep of soil in periglacial or alpine regions, measured in millimeters or centimeters per year. Soil overlying impermeable permafrost becomes oversaturated with water, reducing friction and allowing gravity to pull the material downslope (p. 24).

2) Role of Water in Mass Wasting

Answer: Water increases the weight of slope materials through rainfall, snowfall, or snowmelt, making them heavier and more prone to movement. It also reduces friction along sliding surfaces by seeping into soil and rock, lubricating them. These factors enhance the likelihood of mass wasting events like slides and flows (p. 22).

3) Exfoliation

Answer: Exfoliation is a type of weathering where outer layers of rock separate due to pressure release. When overlying rocks are removed, the underlying rock expands outward under reduced pressure, causing the outer layers to peel off, often forming dome-shaped structures, especially in coarse-grained igneous rocks like granite (p. 18, Fig. 2.8).

4) Weathering and Homogeneity in Rocks

Answer: Homogeneous rocks, like granite, are more resistant to weathering because they lack joints or layers, making them harder to break. In contrast, rocks with joints or layers, such as sedimentary rocks, break more easily as water, temperature, and pressure exploit these weaknesses, accelerating weathering (p. 15).

5) Carbonation

Answer: Carbonation is a chemical weathering process where carbon dioxide in air or soil reacts with minerals like feldspar and carbonates in rocks, especially limestone. In humid climates, water enhances this reaction, causing decomposition as calcium and carbonate ions detach, often simultaneously with solution processes (p. 16).

Q. 6) Draw neat and labelled diagrams for :

1) Freeze and thaw weathering

2) Block disintegration

3) Biological weathering

Q. 7) Answer in detail:

1) Explain with examples the process of weathering happening in Konkan.

Answer:

1) Physical Weathering:

• Freeze-and-Thaw: Though less dominant in Konkan’s tropical climate, higher altitudes in the Western Ghats may experience minor freeze-thaw weathering during cooler seasons, where water in rock cracks freezes, expands, and breaks rocks (p. 16).
• Salt Weathering: In coastal Konkan (e.g., Hareshwar, Raigad), salt crystallization occurs due to alternating wet and dry conditions. Salts like sodium and calcium in rocks expand, splitting grains and forming honeycomb structures (p. 17, Fig. 2.4).
• Block Disintegration: In areas with jointed rocks like basalt, high diurnal temperature ranges cause expansion and contraction along joints, breaking rocks into blocks (p. 17, Fig. 2.7).

2) Chemical Weathering:

• Hydrolysis: Konkan’s high rainfall facilitates hydrolysis, where water reacts with silicate minerals in igneous rocks (e.g., basalt), forming compounds that break the rock (p. 16).
• Solution: Limestone in Konkan reacts with water and air to form carbonic acid, dissolving minerals like calcium and leading to rock decomposition (p. 16).
• Carbonation: In humid Konkan, carbon dioxide reacts with carbonates in rocks, decomposing limestone, enhanced by abundant water (p. 16).
• Oxidation: Iron in rocks oxidizes, forming red iron oxides, altering rock size and color, especially in iron-rich basalts (p. 16).

3) Biological Weathering:

• Tree roots in Konkan’s forested areas penetrate rock cracks, widening them and breaking rocks. Microorganisms like lichens secrete chemicals that erode rock surfaces (p. 19, Fig. 2.9).

4) Anthropogenic Weathering:

• Quarrying and deforestation in Konkan accelerate weathering by exposing rocks to climatic factors and disrupting natural stability (p. 19).
• Example: In Raigad, honeycomb structures at Hareshwar demonstrate combined physical (salt) and chemical (solution) weathering due to coastal conditions.

2) Explain the correlation between Himalayas and mass movements. Give examples wherever necessary.

1) Correlation Factors:

• Relief and Slope: The Himalayas’ steep slopes and high elevation increase the likelihood of mass movements. Steeper slopes lead to rapid movements like landslides and rock falls, unlike gentle slopes with slower creep (p. 22).
• Gravity: As the primary force, gravity pulls loose material downslope, especially on steep Himalayan slopes, driving falls, slides, and flows (p. 22).
• Water: Heavy monsoon rainfall and snowmelt in the Himalayas saturate soils, increasing weight and reducing friction, triggering slides and flows. Melting snow adds water to soils, enhancing instability (p. 22-23).
• Weak Material and Structures: Himalayan rocks, often jointed or containing weak minerals like clay, are prone to breaking. Clay layers prevent water percolation, saturating surface layers and causing slides (p. 22-23).
• Vegetation Loss: Deforestation in the Himalayan foothills, often for agriculture or infrastructure, weakens soil stability by removing root systems, increasing mass wasting risks (p. 23).
• Tectonic Activity: The Himalayas, formed by tectonic forces, experience earthquakes that destabilize slopes, triggering mass movements (p. 25, implied by tectonic forces question).

2) Types of Mass Movements:

• Rock Fall: Common in rocky Himalayan cliffs, where rock material rapidly falls to the base (p. 24). Example: Rock falls in Uttarakhand during road construction.
• Slides: Occur on moderately steep slopes, with soil or rock moving as a single mass. Example: Landslides in Himachal Pradesh during monsoons, burying roads (p. 24).
• Flows: Water-saturated earth flows occur in humid Himalayan regions, burying villages. Example: Kedarnath floods (2013) involved debris flows (p. 24).
• Creep: Slow soil movement along Himalayan hilltops, often unnoticed but continuous (p. 24).
  Solifluction: In periglacial Himalayan regions, oversaturated soil creeps slowly due to permafrost (p. 24).

3) Examples:

• Malin Village Landslide (2014): Though not in the Himalayas, the document’s example of a mudslide near Pune after heavy rainfall (p. 21, Fig. 2.11) parallels Himalayan landslides, where heavy monsoon rains trigger slides.
• Uttarakhand Landslides: Frequent in the Himalayan foothills, especially during monsoons, due to steep slopes, heavy rainfall, and weak rock structures.