NCERT Solutions for Class 11 Geography India Physical Environment Chapter 6: Natural Hazards and Disasters

Chapter at a glance

Exercise Questions

Question 1 (i)

Which one of the following states of India experiences floods frequently?
(a) Bihar (b) West Bengal (c) Assam (d) Uttar Pradesh

Answer

Assam, in the Brahmaputra valley, experiences floods most frequently. (Bihar and West Bengal are also flood-prone.)

3. Assam

Question 1 (ii)

In which one of the following districts of Uttaranchal did Malpa Landslide disaster take place?
(a) Bageshwar (b) Champawat (c) Almora (d) Pithoragarh

Answer

4. Pithoragarh

Question 1 (iii)

Which one of the following states receives floods in the winter months?
(a) Assam (b) West Bengal (c) Kerala (d) Tamil Nadu

Answer

Tamil Nadu receives heavy rain from the north-east monsoon in October–December.

4. Tamil Nadu

Question 1 (iv)

In which of the following rivers is the Majuli River Island situated?
(a) Ganga (b) Brahmaputra (c) Godavari (d) Indus

Answer

2. Brahmaputra

Question 1 (v)

Under which type of natural hazards do blizzards come?
(a) Atmospheric (b) Aquatic (c) Terrestrial (d) Biological

Answer

1. Atmospheric

Question 2 (i)

When can a hazard become a disaster?

Answer

A hazard becomes a disaster when it strikes an area with vulnerable people and causes large-scale loss of life, property and livelihood, disrupting society beyond the capacity of the community to cope with its own resources.

When it hits vulnerable people and causes widespread loss of life and property that the community cannot cope with.

Question 2 (ii)

Why are there more earthquakes in the Himalayas and in the north-eastern region of India?

Answer

The Indian plate is moving north and north-east at about 1 cm a year and colliding with the Eurasian plate. This continuous pressure causes stress to build up in the rocks of the young, still-rising Himalayas and the north-east, which is released as frequent earthquakes along faults.

Because the Indian plate keeps pushing against the Eurasian plate, building stress in the young Himalayan and north-eastern rocks that is released as earthquakes.

Question 2 (iii)

What are the basic requirements for the formation of a cyclone?

Answer

1. A large, continuous supply of warm, moist air — sea surface temperature above 27°C.
2. Strong Coriolis force (not right at the equator).
3. Small variation in vertical wind speed (low vertical wind shear).
4. A pre-existing weak low-pressure area or circulation.
5. Upper-level divergence above the sea-level system.

Warm sea (above 27°C) supplying moist air, strong Coriolis force, low vertical wind shear, a pre-existing low, and upper-level divergence.

Question 2 (iv)

How are the floods in Eastern India different from the ones in Western India?

Answer

• Eastern India (Assam, West Bengal, Bihar, Odisha): floods are frequent and recurrent, caused by heavy monsoon rain, overflowing rivers like the Brahmaputra, Kosi and Gandak with heavy silt loads, flat low-lying deltas and cyclones.
• Western India (Rajasthan, Gujarat): floods are occasional and flash floods, caused by sudden heavy rainfall in usually dry areas with low infiltration and poor drainage.

Eastern floods are recurrent, from heavy monsoon rain and overflowing silt-laden rivers in low plains; western floods are occasional flash floods after sudden heavy rain in dry areas.

Question 2 (v)

Why are there more droughts in Central and Western India?

Answer

Central and western India (Rajasthan, Gujarat, Madhya Pradesh, Marathwada, interior Karnataka) receive low and highly variable monsoon rainfall, as they are far from the sea or in the rain shadow of the Western Ghats. High temperatures and evaporation, sandy soils and over-extraction of groundwater add to water scarcity.

Because these areas get low, erratic rainfall (rain shadow, distance from sea) with high evaporation and overused groundwater.

Question 3 (i)

Identify the Landslide-prone regions of India and suggest some measures to mitigate the disasters caused by these.

Answer

Landslide vulnerability zones

1. Very high: young, unstable mountains — the Himalayas (Uttarakhand, Himachal Pradesh, Jammu and Kashmir), Andaman and Nicobar, high-rainfall areas of the Western Ghats and Nilgiris, the north-east, areas with frequent earthquakes, and areas of heavy human activity (roads, dams, deforestation).
2. High: similar conditions but less intense — parts of the Himalayan states and the north-east except Assam plains.
3. Moderate to low: Trans-Himalayan Ladakh and Spiti, Aravalli hills, rain-shadow areas of the Western and Eastern Ghats and the Deccan plateau; mining areas (Jharkhand, Odisha, Chhattisgarh).
4. Other areas: the plains and deserts are largely free from landslides.

Mitigation measures

• Restrict construction of roads and dams in vulnerable areas; build retaining walls.
• Afforestation and checking deforestation; terrace farming instead of shifting cultivation in the north-east.
• Surface drainage control to prevent water seepage.
• Hazard zonation mapping and early warning; avoiding settlements on unstable slopes.

Most prone: Himalayas, north-east, Western Ghats/Nilgiris and Andaman. Mitigation: limit construction, retaining walls, afforestation, terrace farming, drainage control, hazard mapping and early warning.

Question 3 (ii)

What is vulnerability? Divide India into natural disaster vulnerability zones based on droughts and suggest some mitigation measures.

Answer

Vulnerability is the degree to which a population, area or system is susceptible to harm from a hazard, depending on physical exposure as well as social and economic conditions.

Drought zones

1. Extreme drought-affected areas: most of Rajasthan (west of the Aravallis), Marathwada, and Kachchh in Gujarat (rainfall under 40 cm).
2. Severe drought-prone areas: eastern Rajasthan, much of Madhya Pradesh, eastern Maharashtra, interior Andhra Pradesh and Karnataka, northern Tamil Nadu, southern Jharkhand and interior Odisha.
3. Moderate drought-affected areas: northern Rajasthan, Haryana, southern Uttar Pradesh, the remaining parts of Gujarat, Maharashtra (except Konkan), Jharkhand, Coimbatore plateau in Tamil Nadu and interior Karnataka.

Mitigation measures

• Rainwater harvesting, check dams, watershed development and recharge of groundwater.
• Drought-resistant crops and efficient irrigation (drip and sprinkler).
• Afforestation and soil conservation.
• Inter-basin water transfers; canals (e.g. Indira Gandhi Canal).
• Relief: food and fodder supply, employment schemes, crop insurance.

Vulnerability is susceptibility to harm. Drought zones: extreme (western Rajasthan, Kachchh, Marathwada), severe (eastern Rajasthan, MP, Deccan interiors), moderate (Haryana, south UP, rest of Gujarat and Maharashtra). Mitigation: water harvesting, watersheds, drought-resistant crops, efficient irrigation, afforestation and relief.

Question 3 (iii)

When can developmental activities become the cause of disasters?

Answer

Development becomes a cause of disasters when it ignores environmental limits:

1. Deforestation and road construction on hill slopes destabilise them and cause landslides and floods (e.g. in the Himalayas).
2. Large dams and reservoirs in seismic areas can trigger earthquakes (reservoir-induced seismicity, e.g. Koyna) and displace people.
3. Construction on floodplains and blocking drainage causes urban floods (e.g. Mumbai 2005, Chennai 2015).
4. Mining and quarrying cause land subsidence and landslides.
5. Over-extraction of groundwater leads to droughts and land subsidence.
6. Industrial accidents (Bhopal gas tragedy, 1984) and pollution.
7. Destruction of mangroves increases the impact of cyclones and tsunamis.

When it ignores environmental limits: deforestation and hill roads (landslides), dams in seismic zones, building on floodplains, mining, groundwater overuse, industrial hazards and mangrove destruction.

Topic checklist

• Hazards and disasters; classification
• Earthquakes and tsunami
• Tropical cyclones
• Floods and droughts
• Landslides; disaster management

Total questions answered: 13 of 13