UPSC Static Quiz – Geography : 13 June 2025

Solution: b)

The Peru (Humboldt) Current is a cold, low-salinity ocean current that flows north-westward along the west coast of South America.

• Impact on Atacama Desert: The coldness of the Peru Current cools the air above it, leading to atmospheric stability and inhibiting large-scale precipitation. The presence of the Andes Mountains to the east also creates a rain shadow effect. This combination of factors contributes significantly to the extreme aridity of the Atacama Desert, one of the driest places on Earth.
• Brazil Current: This is a warm current flowing south along the Brazilian coast, associated with warm, moist conditions.
• Falkland Current: This is a cold current originating in the Antarctic region, flowing north along the coast of Argentina, but its primary influence is not on the Atacama.
• Benguela Current: This is a cold current along the western coast of Southern Africa, responsible for the aridity of the Namib Desert, similar to how the Peru Current affects the Atacama.

Solution: b)

Temperature inversion is a condition where a layer of warmer air sits atop a layer of cooler air near the ground, which is a reversal of the normal decrease of temperature with height.

• Favorable conditions for radiation inversion (most common type near the surface):
  • Long winter nights: Allows for extended periods of radiational cooling of the Earth’s surface.
  • Clear skies: Facilitates rapid loss of longwave radiation from the surface to space, leading to significant cooling. Clouds would trap outgoing radiation and keep the surface warmer.
  • Calm winds: Prevents the mixing of the cold air layer near the surface with warmer air above it. Strong winds would cause turbulence and disrupt the inversion.
  • Low humidity/Dry air: Dry air cools and warms more rapidly than moist air. Less water vapour means less absorption of outgoing terrestrial radiation.

Solution: d)

A caldera is a large, cauldron-like hollow that forms shortly after the emptying of a magma chamber in a volcanic eruption.

• Formation: When a large volume of magma is erupted over a short time, the structural support for the rock above the magma chamber is lost. The ground surface then collapses downward into the emptied or partially emptied magma chamber, creating a large depression.
• Size: Calderas are typically much larger and wider than volcanic craters. Craters are generally smaller, circular depressions created by volcanic activity directly around the vent.

Solution: a)

Foehn winds are a type of warm, dry, downslope wind.

• Statement 1 is correct: Foehn winds occur on the leeward (downwind) side of a mountain range. Air is forced to ascend the windward side, cools adiabatically, and loses moisture through precipitation. As it descends on the leeward side, it becomes a Foehn wind.
• Statement 2 is correct: The primary reason for the warmth of Foehn winds is adiabatic compression. As the air descends the leeward slope, it is compressed by increasing atmospheric pressure, causing its temperature to rise at the dry adiabatic lapse rate (which is higher than the saturated adiabatic lapse rate at which it cooled during ascent if it lost moisture). The prior release of latent heat during condensation on the windward side also contributes to the air being warmer than it would otherwise be at the same elevation on the windward side.
• Statement 3 is incorrect: Foehn winds are characteristically dry, not humid. They lead to a significant drop in relative humidity because the air has lost moisture on the windward side and its temperature increases upon descent (warm air can hold more moisture, so relative humidity drops). They are associated with clear skies and rapid snowmelt, not increased precipitation.

Solution: c)

• Statement 1 is correct: At divergent plate boundaries (e.g., mid-ocean ridges), tectonic plates are moving apart, and magma rises to form new oceanic crust. This process is associated with frequent, but typically shallow-focus earthquakes and tensional stresses.
• Statement 2 is incorrect: When two continental plates converge, neither is dense enough to subduct significantly beneath the other. Instead, the crust buckles and is pushed upwards or sideways, forming extensive fold mountain ranges (e.g., the Himalayas, formed by the collision of the Indian and Eurasian plates). While some metamorphism and granitic intrusions can occur, extensive volcanic arcs (lines of volcanoes) are characteristic of ocean-continent or ocean-ocean convergence where subduction of an oceanic plate leads to magma generation.
• Statement 3 is correct: At transform plate boundaries, plates slide horizontally past one another along transform faults (e.g., the San Andreas Fault). This movement is not smooth and often results in the build-up and release of stress, causing powerful earthquakes. Volcanic activity is generally absent at transform boundaries.