Geomorphology Questions and Answers

Answer: C

Under Strahler's ordering (printed 'Strahlen'), the higher order stream will remain same.

In Strahler's scheme the smallest fingertip streams are first order. A stream's order rises by one only where two streams of the same order meet: two first-order streams make a second-order stream, two second-order streams make a third-order stream. When a lower-order stream joins a higher-order one, the main stream keeps its order.

So a second-order stream joining a third-order stream leaves it third order. It does not increase (that needs another third-order stream), it can never decrease, and orders are not added together, which is how Shreve's magnitude, not Strahler's order, is calculated.

Answer: D

The stream left with little water after river capture is a misfit river.

In river capture, a more actively eroding stream (the captor or pirate) cuts back into the basin of a neighbour and diverts its headwaters. The neighbour below the point of capture is beheaded: it keeps its old valley but loses most of its water, so it becomes too small for the valley it flows in, a misfit stream.

The captor river is the one that gains the water, and the captured portion is the headwater diverted into it, so neither is left short of water. A rejuvenated river is one whose erosive power has been renewed, which happens to the captor at the elbow of capture, not to the beheaded stream.

Answer: B

The key's factors are climate, vegetation cover, rock structure and topography, so the answer is (2), (3), (4) and (5).

The standard controls on weathering are climate (temperature and moisture decide whether mechanical or chemical weathering dominates and how fast it runs), the rock itself (its structure, joints and minerals), vegetation (roots that split rock and organic acids that attack it) and topography (slope and aspect, which control drainage and how fast debris is removed), together with time.

Soil is mainly a product of weathering rather than one of its governing factors, which is why the key leaves it out. Every other option includes soil and drops one of the four controls.

Answer: D

The group made entirely by erosion is Cirques, V-shaped valleys, Demoiselles.

A cirque is an armchair-shaped hollow carved by a glacier at its head, a V-shaped valley is cut by river downcutting, and demoiselles (earth pillars) are columns left standing where a capping stone protects softer material from erosion by rain and wind. All three are erosional landforms.

Each other group contains depositional features. Drumlins and moraines are glacial deposits; a natural levee is built by river floods; eskers and outwash plains are laid down by meltwater. Aretes, U-shaped valleys, ventifacts and fjords are erosional, but their groups are spoiled by those depositional members.

Answer: A

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

Assertion (A) is correct: deflation basins (blowouts) are erosional hollows in deserts, and they range from small dips to depressions many kilometres across. The Qattara Depression in Egypt, which reaches more than 130 m below sea level, is often cited as a large example in whose formation deflation played a part.

Reason (R) is the cause: deflation is the lifting and removal of loose sand and dust by the wind, which lowers the surface until the water table or a resistant layer is reached. Since (R) gives the process that makes the basins, it explains (A), so the other options are wrong.

Answer: C

Oceanic crust is mainly composed of basalt.

Oceanic crust forms at mid-ocean ridges, where magma from the mantle rises and solidifies. Its upper layers are basalt lavas and dykes, with its coarse-grained equivalent, gabbro, below. That basaltic (sima) composition makes it denser and thinner than continental crust.

Granite is the characteristic rock of the continental crust (sial). Andesite is typical of volcanic arcs above subduction zones, such as the Andes, rather than of the ocean floor. Mud is a sediment that may lie on top of the crust, not the crust itself.

Answer: B

A natural levee is built during periods of overbank flooding.

When a river overflows its banks, the water spreading onto the floodplain slows down sharply at the channel edge and drops its coarser sediment there. Repeated floods build low ridges along both banks, highest next to the channel and sloping away from it.

Levees are depositional, not erosional, features. They are typical of lowland floodplains rather than mountainous terrain, and they are well developed along meandering rivers such as the lower Mississippi, so the other three statements are wrong.

Answer: D

Accelerated erosion is not associated with an increase in the thickness of the soil profile.

Accelerated (human-induced) erosion removes soil faster than it forms, so the profile becomes thinner, the topsoil is stripped and subsoil is exposed. It is the opposite of soil thickening.

The other three are its typical signs. Sheet wash concentrates into rills, rills deepen and widen into gullies, and the eroded soil is carried into streams, increasing their sediment load.

Answer: C

The Chambal has not developed a megafan.

Megafans are huge fan-shaped bodies of sediment built where rivers leave a mountain front and spread over a subsiding plain. In the Ganga plain the Himalayan rivers Kosi and Gandak have built large megafans, and the Son, flowing north from the peninsular plateau, has built one on the southern side of the plain.

The Chambal flows north-east across the plateau of Malwa and the Vindhyan region in a deeply incised valley (with its famous ravines) and joins the Yamuna. It does not debouch onto a subsiding plain to build a megafan.

Answer: C

The most common and widespread dune type in the Thar is the parabolic dune.

Parabolic dunes are U- or V-shaped, with their arms pointing upwind and anchored by vegetation. The Thar is a relatively humid, partly vegetated desert under strong south-westerly monsoon winds, conditions that favour parabolic dunes, which studies of the Thar describe as its dominant dune type.

Barchans, crescent dunes with horns pointing downwind, form where sand is limited and vegetation absent, and occur only locally in the drier west. Star dunes need multidirectional winds and are rare, and seif (linear) dunes are present but less widespread.