Geomorphology Questions and Answers

Answer: A

The answer is a deferred tributary, also called a yazoo stream.

Natural levees on the banks of a large river stand higher than the floodplain behind them. A tributary crossing the floodplain cannot break through the levee, so it runs parallel to the main river, often for long distances, before it finally joins it downstream. The Yazoo River, which runs beside the Mississippi before joining it at Vicksburg, gives the type its other name.

An anabranch is a channel that leaves a river and rejoins it downstream; anastomosing describes a pattern of several interconnected channels. Solitary is not a recognised class of tributary.

Answer: D

The signs of rejuvenation are (1), (3) and (4): incised meanders, nick points and paired terraces.

Rejuvenation gives a river new erosive power, usually through uplift of the land or a fall in base level. The river cuts down into its old floor. Meanders that had formed on a floodplain become entrenched as incised meanders, a knick point (a break in the long profile, often a waterfall) migrates upstream from the point where downcutting began, and the remains of the old floodplain are left on both sides of the valley at the same height as paired terraces.

Unpaired terraces, at different heights on the two sides, form when a river shifts sideways while cutting down slowly and continuously, so they are not a sign of rejuvenation. That rules out options containing (2).

Answer: B

The area is the water divide.

A water divide (watershed line) is the ridge or high ground separating two drainage basins. It is the highest line in the drainage network, and streams on its two sides flow away from it in opposite directions.

A valley is the low ground where the streams themselves run, and a confluence is the point where two streams meet, so both are lower parts of the network where flows converge rather than diverge. A mid slope lies between the divide and the valley floor and is neither the highest point nor a place where directions reverse.

Answer: A

The key gives Dust storms.

A turbidity current is a density current: a flow made heavier than its surroundings by the sediment it carries in suspension, which then moves along the ground under gravity. In arid regions the atmospheric counterpart is the dust storm, such as the haboob of the Sudan, where a mass of cold, dust-laden air advances along the ground as a dense wall, so dust storms are the arid form of such currents.

A thunderstorm is a convective cloud system, a tornado a narrow rotating vortex and a cyclone a large low-pressure system. None of them is defined by a load of suspended sediment moving as a density current.

Answer: C

Statements (i), (ii) and (iii) are correct, so the answer is (i), (ii) and (iii) only.

A stream carries its load in three ways: dissolved load as ions in solution (i), bed load of sand, gravel and larger particles rolling, sliding and saltating along the bottom (ii), and suspended load of fine clay and silt held up by turbulence (iii).

Statement (iv) is wrong: in most rivers the suspended load is the largest part of the total, and the bed load is usually the smallest. That rules out the option with (iv) and the options leaving out (i) or (iii).

Answer: A

The answer is Both (A) and (R) are true and (R) is the correct explanation of (A).

Raised shorelines, old beaches and wave-cut platforms now standing above sea level, are common around the Pacific, for example in Japan, New Zealand, Chile and California.

The reason is the active tectonics of the Pacific margins. Along the mountain belts and island arcs of the 'Ring of Fire', subduction and faulting repeatedly uplift the coast, often by metres in a single great earthquake, lifting former shorelines out of reach of the sea. So R explains A, and the options denying either statement or the link are wrong.

Answer: B

Littoral drift along a straight shore builds a Sandspit.

Where waves approach a coast at an angle, longshore (littoral) drift moves sand along the beach. Where the coastline turns, for example at a bay mouth or headland, the drift continues in its original direction and deposits a ridge of sand that grows out into open water, attached to land at one end: a spit.

A pocket beach is a small beach trapped between headlands, where littoral drift is limited. An abrasion platform and a stack are erosional features carved by waves, not deposits of drifting sand.

Answer: A

These are insequent streams.

Insequent streams develop without any clear control by the dip or strike of the rocks, usually on uniform material, and branch haphazardly in a dendritic pattern.

Consequent streams flow down the original slope of the land, in the direction of dip. Obsequent streams flow opposite to the dip, and resequent streams flow in the same direction as the original consequents but develop at a lower level later. All three are structurally controlled.

Answer: A

The answer is (1) and (3): the jigsaw fit of the continents and the fossils found in different areas.

In The Origin of Continents and Oceans (1915) Alfred Wegener argued that the coasts of South America and Africa fit together like pieces of a puzzle, and that identical fossils, such as the reptile Mesosaurus and the plant Glossopteris, occur on continents now separated by oceans. He also used matching rock formations and evidence of past glaciation.

Convection in the mantle was proposed as the driving force by Arthur Holmes in 1928-29; Wegener himself relied on a pole-fleeing force and tidal forces, which was the theory's weak point. Transcurrent (transform) faults belong to plate tectonics in the 1960s, through J. Tuzo Wilson. So every option adding (2) or (4) is wrong.

Answer: A

Both (A) and (R) are true and (R) is the correct explanation of (A).

Laterite soils form in hot regions with heavy rainfall and alternating wet and dry seasons. The heavy rain leaches out silica and soluble bases such as calcium, magnesium and potassium, and much of the humus, leaving a residue rich in iron and aluminium oxides. That is why laterites are poor in nutrients and need heavy manuring before they can be cropped.

So leaching under high rainfall is the very reason laterites are infertile, which makes (R) the explanation of (A) and rules out the options that call either statement false or deny the link.