Shaping of the Earth's Surface — NCERT Solutions

The sudden flood in Chamoli was likely caused by a combination of glacial melting, collapse of ice or loose material, and possibly a landslide or avalanche that blocked and then released water. The chapter explains that GLOFs and sudden floods can happen when glaciers melt rapidly, lakes or ice dams fail, or landslides/avalanches disturb stored water in mountainous regions.

The movement associated with internal forces is driven by heat from the Earth's core, which causes convection currents in the mantle. These currents move molten material and help drive plate movements.

The physiographic divisions studied earlier can be related to endogenic forces as follows:

• Mountains: formed by folding and faulting due to plate movement.
• Plateaus: often formed by uplift and volcanic activity.
• Plains: may form from the deposition of sediments brought by rivers, though their broad shape can also be influenced by crustal movements.
• Valleys and rift valleys: formed by faulting and tectonic movement.
• Volcanic landforms: created by volcanic eruptions.

Thus, endogenic forces create major relief features by pushing, folding, breaking, and uplifting the Earth's crust.

Earthquakes occur frequently because the Earth's crust is broken into tectonic plates that are constantly moving. They occur mainly along plate boundaries, where plates collide, move apart, or slide past each other. Earthquakes are common in these regions because stress builds up in the rocks and is suddenly released.

It is not possible to predict earthquakes exactly with certainty in advance. Scientists can identify earthquake-prone zones and estimate risk, but they cannot tell the exact time, place, and magnitude of an earthquake beforehand.

Plate movements are responsible for the distribution of earthquakes and volcanoes because these events happen mainly at plate boundaries.

• At a convergent boundary, plates collide. This can cause earthquakes and, where an oceanic plate sinks beneath another plate, volcanic activity.
• At a divergent boundary, plates move apart. Magma rises and forms new crust, often producing volcanoes and earthquakes.
• At a transform boundary, plates slide past each other, causing earthquakes.

Therefore, earthquakes and volcanoes are concentrated where plates meet, especially around the Pacific Ring of Fire.

Deforestation and erosion are closely related. When trees are cut down, the roots that hold the soil together are removed. Without plant cover, rain and wind can easily wash away or blow away the topsoil. So, deforestation increases soil erosion, and erosion becomes more severe in deforested areas.

A plan to protect land in a local area from erosion may include:

• Planting trees and grass to bind the soil.
• Building contour trenches, bunds, and terraces on slopes.
• Keeping drains clear so water does not flow forcefully over land.
• Avoiding deforestation, mining, and construction on unstable slopes.
• Using check dams and small barriers to slow water flow.
• Protecting riverbanks with vegetation.
• Educating people to use land carefully and prevent overgrazing.

These steps reduce the speed of water and wind and help keep soil in place.

The disasters a region may experience depend on its landforms and climate. For example:

• Mountain regions: landslides, avalanches, GLOFs.
• Coastal regions: coastal erosion, cyclones, floods.
• Dry regions: dust storms.
• Earthquake-prone regions: earthquakes and sometimes landslides.

A classroom mitigation plan should include:

• identifying local hazards,
• making an emergency contact list,
• preparing an evacuation route,
• keeping a first-aid kit,
• practising safety drills,
• listening to warnings and official instructions,
• and learning how to help injured people safely.

If I stay in an earthquake-prone region, I will:

• build or live in a quake-resistant house if possible,
• keep heavy objects secured,
• know safe places like under a sturdy table or beside an inner wall,
• stay away from windows and glass,
• keep an emergency kit ready,
• learn and practise Drop, Cover, and Hold,
• turn off gas and electricity if needed after shaking,
• follow official warnings and evacuation instructions.

These precautions can reduce injury and damage.

A past disaster in my region can be documented by describing:

• the event and when it happened,
• the causes,
• the damage to people, homes, roads, crops, and public services,
• the effect on human activities such as farming, transport, trade, education, and jobs,
• and the recovery or relief measures taken afterwards.

For example, if it was a flood, it may have destroyed crops, damaged houses and roads, disrupted transport, and affected schooling and livelihoods. If it was an earthquake, it may have damaged buildings, caused fear, and interrupted economic activities.