Geophysical Phenomena — Practice Questions
UPSC Prelims-pattern practice questions on volcanoes, intrusive landforms, earthquakes, cyclones and the shrinking Aral Sea, with full explanations.
Questions
These are original UPSC-pattern practice questions. Attempt each one before revealing the answer.
Consider the following statements about shield volcanoes:
- They are built mainly by fluid basaltic lava.
- They have a steep, conical shape.
- The volcanoes of Hawaii are examples.
Which of the statements given above is/are correct?
Solution
- Statement 1 — correct. Low-viscosity basaltic lava flows easily over long distances.
- Statement 2 — wrong. Shield volcanoes are broad and gently sloping. Steep cones belong to composite volcanoes such as Fuji, built from viscous andesitic lava and ash.
- Statement 3 — correct. Mauna Loa and Kīlauea are classic shield volcanoes.
Answer: B
A vertical, wall-like sheet of solidified magma that cuts across the layers of the surrounding rock is called a:
Solution
A dyke cuts across rock layers vertically or steeply; dykes are common in the Deccan Traps and acted as feeders for lava flows.
- Sill — horizontal, parallel to the layers.
- Laccolith — dome-shaped with a flat base.
- Batholith — huge, deep granite body.
Answer: D
Which one of the following Indian earthquakes is the most widely cited example of reservoir-induced seismicity?
Solution
The Koyna earthquake (December 1967, Maharashtra) occurred near the Koyna dam after its reservoir was filled and is the classic Indian case of reservoir-induced seismicity.
Latur (1993) hit the stable peninsular shield; Bhuj (2001) is linked to faults in Kachchh; Uttarkashi (1991) to Himalayan tectonics.
Answer: A
Tropical cyclones are almost absent from which one of the following ocean regions?
Solution
The South Atlantic is unusually cool for its latitude (cold Benguela current, upwelling) and has strong vertical wind shear, so tropical cyclones are extremely rare there.
The Bay of Bengal (cyclones), western North Pacific (typhoons) and Caribbean (hurricanes) are among the most active basins.
Answer: C
The drastic shrinking of the Aral Sea since the 1960s is mainly attributed to:
Solution
Soviet-era irrigation projects diverted the Amu Darya and Syr Darya — the Aral Sea’s main feeder rivers — mostly to grow cotton. With inflow sharply reduced, the sea shrank and split into smaller water bodies; fisheries collapsed, and salt- and dust-laden winds from the exposed bed harmed health and farmland.
The Volga drains into the Caspian Sea, so option D is a distractor.
Answer: A
Mains
What are glacial lake outburst floods (GLOFs)? Discuss why the risk of GLOFs is rising in the Indian Himalaya and suggest measures to manage it.
Solution
Introduction: A glacial lake outburst flood is the sudden release of water from a lake dammed by glacial ice or moraine, when the dam fails. Such floods can travel tens of kilometres downstream in hours, as seen above Kedarnath (Chorabari lake, June 2013) and from South Lhonak Lake in Sikkim (October 2023), which flooded the Teesta valley.
Body:
- Why risk is rising: glacier retreat with warming creates and enlarges moraine-dammed lakes; extreme rainfall and cloudbursts; landslides or ice avalanches falling into lakes; earthquakes in a seismically active belt.
- Exposure: settlements, roads and hydropower projects built along narrow valleys downstream.
- Measures: inventory and satellite monitoring of glacial lakes; hazard mapping; lowering lake levels by siphoning or controlled outlets; early-warning sensors with community alarms; land-use zoning; climate-proof design of dams and bridges; NDMA guidelines on GLOF management.
Conclusion: GLOFs are a clear case of a “change in a critical geographical feature” turning into a disaster. Monitoring and early warning are cheap compared with downstream losses.