Geomorphology Questions and Answers

Answer: B

The kettle hole is not a karst feature.

A kettle hole is a glacial landform: a depression in outwash or till left when a buried block of stagnant ice melted and the sediment above it collapsed. It has nothing to do with the dissolution of rock.

The other three are karst forms produced by the solution of limestone. A sink hole is a closed depression where surface water drains underground; doline is the formal term for such a depression; and an uvala is a larger compound depression formed where several dolines merge.

Answer: C

The movement that is essentially vertical is subsidence.

Subsidence is the sinking of the ground surface with little or no horizontal displacement. It happens when support is removed from below, as over solution cavities in limestone, collapsed mine workings, or sediments compacting after groundwater or oil is withdrawn.

The other movements all travel downslope and so have a large horizontal component. A landslide moves a mass along a failure surface, creep is the slow downhill drift of soil, and a mudflow is a fluid mass of water-saturated fine debris flowing down a slope or channel.

Answer: C

The correct order of increasing speed is Creep-rotational landslide-debris flow-rock fall.

Creep moves soil at millimetres to centimetres a year and is the slowest mass movement. A rotational landslide (slump) moves a coherent block over minutes to days. A debris flow is a fast-moving slurry that can travel metres per second, and a rock fall, free fall through the air, is the fastest of all.

Option A puts creep after solifluction and debris flow after rock fall; option B ends with earth flow, which is slower than a rock fall; and option D ends with solifluction, which is almost as slow as creep. Each breaks the order somewhere.

Answer: A

A braided pattern develops with a significant increase in the amount of coarse sediment load.

When a river is supplied with more bedload sand and gravel than it can carry, it drops the excess as bars in mid-channel. Flow splits around the bars into many shallow, interlacing channels, and the bars shift with every flood. Steep gradients and highly variable discharge, as below glaciers, encourage the same result.

A decrease in coarse load would let the river concentrate into a single channel. Increasing sinuosity is the meandering tendency, the opposite style. Wash load is the fine clay and silt carried in suspension, which plays little part in building braid bars.

Answer: C

Ice crystal growth is not a chemical weathering process.

The growth of ice in cracks and pores (frost wedging) and of ice lenses in soil pries rock apart by pressure. It breaks rock into smaller pieces without changing its minerals, so it is mechanical (physical) weathering.

The other three alter mineral chemistry. Hydrolysis breaks down silicates such as feldspar into clay by reaction with water. Oxidation turns ferrous iron in minerals into ferric oxides and hydroxides. The carbonic acid reaction (carbonation) dissolves limestone and attacks silicates through carbon dioxide dissolved in rainwater.

Answer: A

The thickest known loess is in China.

The Loess Plateau of the middle Huang He (Yellow River) basin carries wind-blown silt that is commonly 100 to 200 m thick and locally more than 300 m, the greatest loess thickness recorded anywhere. The dust was blown out of the Gobi and the inner Asian deserts during the Pleistocene and settled downwind, and its easy erosion is what gives the Yellow River its silt and its colour.

The U.S.A. has loess along the Mississippi and Missouri valleys and in the Palouse, but it is far thinner. Mongolia is largely a source area of the dust rather than its sink, and Afghanistan has only local loess patches.

Answer: D

Laterite is produced by leaching and oxidation.

Under the heavy seasonal rain and high temperature of the humid tropics, percolating water leaches silica, lime and other bases out of the weathered rock. What remains is enriched in hydrated oxides of iron and aluminium, and the oxidation of the iron gives laterite its red colour and lets it harden into a brick-like crust on exposure to air.

Carbonation and calcification are processes of limestone and dry-climate soils, where lime stays in the profile rather than being removed, so options with them describe the opposite of laterization. Hydrolysis does help break down the silicate minerals, but the pair the standard account names for laterite is leaching followed by oxidation.

Answer: D

Eskers (the paper's 'Eskens') are formed by fluvio-glacial deposition.

An esker is a long, narrow, winding ridge of stratified sand and gravel. It is laid down by meltwater streams flowing in tunnels within or beneath a glacier; when the ice melts away, the stream-bed deposits are left standing as a ridge.

Because the material is sorted and bedded by running water, it is fluvio-glacial, not glacial: purely glacial deposition gives unsorted till in moraines and drumlins. Erosion of either kind removes material and cannot build a ridge, so both erosion options are wrong.

Answer: B

Both statements are true but the Reason does not explain the Assertion, so the answer is that (R) is not the correct explanation of (A).

Granite is an intrusive (plutonic) rock: its magma cooled slowly deep in the crust, giving the minerals time to grow large crystals. Basalt is an extrusive rock: lava cooled quickly at the surface, so its crystals are fine. Crystal size is therefore explained by the rate of cooling.

The Reason is also true, since basalt is a mafic rock rich in iron and magnesium minerals while granite is felsic and rich in quartz and feldspar. But mineral composition does not decide crystal size, so the Reason is a true statement that does not explain the Assertion. That rules out the first option, and both one-false options.

Answer: A

The correct matching is (2) (1) (4) (3): hydraulic action - geo, plucking - cirques, deflation - desert pavements, solution - terra rossa.

• Hydraulic action of waves forcing water and air into joints in a sea cliff opens a narrow inlet called a geo.
• Plucking by glacier ice tears blocks from the back wall of a hollow, deepening it into a cirque.
• Deflation by wind removes the fine particles from a desert surface and leaves a lag of stones, the desert pavement.
• Solution of limestone leaves its insoluble clay and iron residue as the red soil terra rossa.

Option D swaps deflation and solution, and options B and C pair plucking or hydraulic action with the wrong feature.