MEV 012 Solved Guess Paper 2026 for Earth Processes, IGNOU Master of Science (Environmental Science) MSCENV

Weathering and its various types

Question: What is meant by weathering? Describe its various types with suitable examples.

Meaning: "Weathering is breaking of surface rocks into sediments by any natural process." Sediments come from a pre-existing rock broken down physically or chemically, a process that can take millions of years depending on climate and rock type. The book recognises three types.

Physical (mechanical) weathering

1. Temperature: rocks expand when heated and contract when cooled, and the unequal stress opens cracks, especially in deserts and high mountains.
2. Pressure release: unloading creates joints, and exfoliation peels off curved sheets like an onion, which is common in granite.
3. Abrasion: particles carried by wind, water or ice grind the surfaces of larger rocks.
4. Freeze-thaw: water in cracks freezes at night, expands by about one-tenth and wedges the rock apart.
5. Hydraulic action and gravity: waves force water into cliff cracks, and loosened material falls downslope as rockslides and creep, piling up as talus.

Chemical weathering

1. Dissolution: carbonic acid dissolves calcite in limestone.
2. Carbonation: feldspar in granite reacts with CO₂ and changes to kaolin (kaolinisation).
3. Oxidation: pyrite combines with oxygen to form limonite, releasing sulphur.
4. Hydration: anhydrite takes up water and becomes gypsum.

Biological weathering

1. Burrowing organisms mix material (pedoturbation) and expose fresh surfaces.
2. Growing roots wedge rocks apart.
3. CO₂ from respiration and decay makes water more acidic, and lichens, fungi and bacteria release organic acids that attack minerals.

Conclusion: All three types usually act together. Their pace depends on parent rock, climate, soil cover, slope and how long the surface stays exposed.

Tropical and temperate cyclones compared

Question: Differentiate between tropical and temperate cyclones with suitable examples.

Meaning: "The atmospheric disturbances which involve a closed circulation about a low pressure centre, anticlockwise in the northern hemisphere and clockwise in the southern hemisphere, are called cyclones." They are of two types.

Temperate (extra-tropical) cyclones

1. They form between 35° and 60° latitude where two contrasting air masses meet and fronts develop, so their origin is dynamic.
2. Under the polar front theory they pass through six stages, ending in occlusion and dissipation.
3. Four fronts are involved: cold, warm, occluded and stationary.

Tropical cyclones

1. They form over warm oceans in the low latitudes, not right at the equator, because the Coriolis force there is too weak.
2. The calm, low-pressure centre is the eye, circled by violent winds of 120 to 200 km/hr.
3. They are called typhoons near China and Japan, hurricanes near North America and willy-willies near Australia.

Conclusion: Tropical cyclones are intense, heat-driven storms with a calm eye, while temperate cyclones are broad frontal systems. Both bring heavy rain but differ sharply in origin and structure.

The hydrological cycle and distribution of water

Question: Describe the hydrological cycle. Explain the distribution of water in the Earth's crust.

Meaning: "The exchange of water among different reservoirs of the globe is known as the hydrological cycle." Energy from the Sun drives it, and its reservoirs are the oceans, the atmosphere, ground water and runoff from land.

Distribution of water

1. Oceans hold about 96.5% of the Earth's water; only about 2.5% of all water is fresh.
2. Glaciers and ice caps are the largest store of fresh water, about 68.7%, and they regulate the flow of major rivers.
3. Ground water holds about 1.7% of all water and roughly 30.1% of fresh water.
4. The atmosphere is the only reservoir that holds water as liquid, ice and vapour at once.

Working of the cycle

1. Solar heat evaporates water; the vapour rises, cools by adiabatic expansion and condenses on aerosols to form clouds.
2. Winds carry it until it falls as rain or snow and is stored in glaciers, lakes, rivers and ground water.
3. Runoff returns stored water to the oceans, completing the ocean to atmosphere to land to ocean loop.

Conclusion: Driven by the Sun, the cycle keeps moving a fixed stock of water among oceans, air, ice, surface water and ground water, with the ocean as the dominant reservoir.

Types of natural hazards, and hazard vs disaster

Question: Explain the various types of natural hazards. Differentiate between hazards and disasters with examples.

Meaning: Burton et al. (1978) define hazards as "those elements of the physical environment, harmful to man and caused by forces extraneous to him." A disaster happens when an extreme event goes beyond a community's ability to cope. A volcanic eruption in an empty region is only a natural phenomenon; it becomes a hazard when it threatens life and property.

Classification of hazards

1. Natural hazards come from purely natural processes, such as earthquakes and floods.
2. Quasi-natural hazards come from nature and human activity together, such as smog and desertification.
3. Technological hazards come directly from human activity, such as an accidental chemical or radiation release.

Other categories

1. Catastrophic hazards have worldwide effects, like very large eruptions and epidemics.
2. Secondary hazards follow a primary event, such as a fire, landslide or tsunami after an earthquake.
3. Chronic hazards build up slowly, such as famine and resource degradation.
4. Hazards also differ in speed of onset, spread over space and spacing over time.

Dimensions of hazard

Impact depends mainly on magnitude, the energy released, and frequency, how often the event recurs. As a rule, the bigger the event, the rarer it is.

Conclusion: A hazard is the potential threat; a disaster is the harm that follows when that threat overwhelms a community.

Impacts of earthquakes on society

Question: Describe the various impacts caused by earthquakes on society.

Meaning: "The earthquakes were alone responsible for deaths of around 2 million people in the last century" (Grotzinger and Jordan, 2014). Major recent examples include Bhuj 2001, Sumatra 2004, Tohoku 2011 and Nepal 2015.

Impacts on life and property

1. Buildings, dams and power plants collapse, causing heavy loss of life and property.
2. Densely populated quake zones suffer most, as people are trapped under rubble.
3. Losses multiply wherever building codes are ignored.
4. National economies take a hit, as Japan's did after the 2011 earthquake.

Secondary impacts

1. Earthquakes trigger tsunamis, landslides and avalanches.
2. Liquefaction makes water-saturated ground flow like liquid, bringing down buildings and bridges.
3. Broken gas lines and power lines start fires; fire drove much of the roughly 0.14 million death toll of the 1923 Kanto earthquake in Tokyo and Yokohama.
4. Damage to nuclear plants can release radioactive material, as seen at Fukushima after the 2011 Tohoku earthquake.

Conclusion: Earthquakes kill and destroy both directly, through collapse, and indirectly, through tsunamis, landslides, liquefaction and fire. The toll is heaviest where crowded cities lack earthquake-resistant construction.