Geomorphology Questions and Answers

Answer: B

Attrition is the reduction of size of a particle in transit.

As a river, the sea or the wind carries pebbles and sand grains, the particles knock against one another. Each collision chips off fragments, so the load becomes progressively smaller, smoother and rounder downstream. The tool and the target are both moving load, which is what defines attrition.

The other options describe different processes. Wearing down a platform or a channel bed by moving sediment is abrasion (corrasion), where the load acts on the fixed surface. Disintegration of a rock in place is weathering, not erosion during transport. A core stone is the rounded unweathered block left inside a mass of rock rotted by spheroidal chemical weathering, which has nothing to do with transport.

Answer: D

A bergschrund belongs to glacial processes.

It is the deep crevasse that opens at the head of a valley glacier or cirque glacier, where the moving ice pulls away from the ice and rock still frozen to the back wall. Meltwater entering the gap freezes and thaws against the rock, loosening blocks that the glacier then plucks away, so the bergschrund helps steepen the headwall and deepen the cirque.

Coastal processes work through waves, tides and currents; aeolian processes through wind, producing dunes and yardangs; fluvial processes through running water, producing valleys, meanders and deltas. None of them produces a crevasse in ice, so the other three options are wrong.

Answer: C

The scientist is Dutton.

The American geologist Clarence E. Dutton coined the word isostasy in 1889 for the state of balance in which blocks of the crust float on the denser material beneath, standing higher where they are thicker or lighter. The underlying ideas had been put forward earlier by J. H. Pratt and G. B. Airy in the 1850s, which is why the question says Dutton is also credited.

The other names were Dutton's colleagues in the western surveys of the United States, but are known for other work: John Wesley Powell for exploring the Colorado River and introducing the base level of erosion, G. K. Gilbert for the laws of land sculpture and his study of Lake Bonneville, and W J McGee for his work on pediments and sheetfloods. None of them gave the concept its name.

Answer: C

The key's answer is P waves are refracted and S waves are absorbed by the mantle.

Seismographs between about 104° and 140° of arc from an epicentre record no direct P or S waves. P waves striking the core-mantle boundary are bent (refracted) sharply as their speed drops in the liquid outer core, so they emerge beyond 140° and leave a gap. S waves are shear waves, which cannot travel through a liquid, so they do not cross the outer core at all and are missing everywhere beyond about 104°.

Strictly, the S waves are stopped by the liquid outer core rather than by the mantle, which is solid and carries S waves freely; the option set omits that wording, and the key takes the refraction of P and loss of S as the point. The other options are wrong: the waves are not absorbed in the shadow zone itself, not all waves are lost, and it is the P waves, not the S waves, that are refracted.

Answer: A

Petroleum reserves are found in sedimentary rock areas.

Petroleum forms from the remains of marine plankton and other organisms buried in fine sediments and slowly altered by heat and pressure. It then migrates into porous sedimentary reservoir rocks such as sandstone and limestone, where it is trapped under impermeable shale or salt. Sedimentary basins, like Bombay High and the Assam shelf, are therefore where oil is sought.

Igneous and volcanic rocks form from molten magma, which would destroy any organic matter, and metamorphic rocks have been heated and deformed too much for oil to survive. They are not petroleum-bearing.

Answer: D

The process described is erosion.

Erosion is the removal of rock and soil by moving agents: running water, wind, glaciers and waves. The kinetic energy of the moving medium, and of the material it carries, acts on the surface it moves over, abrading and plucking away particles. That interaction between moving material and the surface beneath it is what the definition describes.

Weathering is the breakdown of rock in place, without movement. Mass movement is the downslope movement of material under gravity, and transport is the carrying away of material once it has been eroded, not the attack on the surface itself.

Answer: D

Steep gradients accelerate stream erosion.

A stream's ability to erode depends on its velocity and energy, and velocity rises with the slope of the channel. On a steep gradient, typically in the upper course, water flows fast and erodes vertically, cutting V-shaped valleys, gorges and waterfalls.

Flat flood plains and natural levees belong to the lower course, where the gradient is gentle, velocity falls, and the river deposits rather than erodes; levees are themselves depositional features. Stream flow is simply the presence of moving water; it is the steepness that speeds the erosion.

Answer: B

Karst topography develops through groundwater erosion.

In limestone and dolomite areas, rainwater charged with carbon dioxide forms weak carbonic acid that dissolves calcium carbonate as it seeps underground. This solution by groundwater produces sinkholes, swallow holes, dolines, uvalas, caves and underground drainage, and deposition from the same water forms stalactites and stalagmites. The name comes from the Karst region of the Dinaric Alps.

Glaciers, surface streams and waves produce their own landform families (cirques and moraines, valleys and meanders, cliffs and stacks), but not karst.

Answer: B

The correct matching is a-2, b-3, c-4, d-1.

• W. M. Davis developed the cycle of erosion from his study of the landscapes of New England.
• G. K. Gilbert made his classic study of laccoliths and stream erosion in the Henry Mountains of Utah (1877).
• L. C. King based his theory of pediplanation on the landscapes of South Africa.
• Walther Penck worked on the Alps and the Andes, developing his model of slope development.

Every other code gives at least one of these scientists the wrong region.

Answer: D

The answer is more than three.

Pangea, assembled about 300 million years ago, was only the latest of several supercontinents. Geologists reconstruct earlier ones, among them Rodinia (about 1.1 billion to 750 million years ago), Columbia or Nuna (about 1.8 billion years ago) and Kenorland (about 2.7 billion years ago), with further proposed assemblies such as Vaalbara, Ur and Pannotia. Continents have gathered and split repeatedly in what is called the supercontinent cycle.

The exact list is debated, but even the conservative reconstructions count more than three, so zero, one and three are all too few.