Geomorphology Questions and Answers

Answer: B

A blind valley is a Karst Valley.

In limestone (karst) country a surface stream may disappear underground through a swallow hole or sinkhole. The valley it has cut then ends abruptly in a closed, steep wall at that point, with no surface outlet downstream, which is why it is called blind.

Glacial valleys are U-shaped troughs carved by ice, rift valleys are formed by faulting as the crust is pulled apart, and intermontane valleys lie between mountain ranges. None of them ends where a river sinks into soluble rock.

Answer: B

The erosional landform is the Sea arch.

Waves attack a headland from both sides, enlarging joints into caves; when two caves meet through the headland they form a sea arch. Further erosion collapses the arch, leaving a stack.

A spit is a ridge of sand or shingle built out from the shore by longshore drift, and a tombolo is a similar deposit joining an island to the mainland, so both are depositional. An estuary is a river mouth drowned by a rise in sea level, a product of submergence rather than wave erosion.

Answer: B

The indicator is an elevated marine terrace.

A marine terrace is a wave-cut platform formed at sea level. Finding one raised above the present shore means the sea once stood higher relative to the land, so either sea level has fallen or the land has been uplifted. Stepped terraces record repeated episodes of uplift.

An estuary indicates the opposite, a drowned river valley produced by submergence. A tombolo and coastal dunes are depositional features that form at the present shoreline and say nothing about a change of level.

Answer: A

Jointed and faulted rocks develop a rectangular drainage pattern.

Joints and faults are zones of weakness that streams erode preferentially. Where two sets of fractures cross at roughly right angles, the main streams and their tributaries follow them and join at right angles, giving a rectangular pattern.

A parallel pattern forms on a uniform, steep slope, a centripetal pattern drains into a central basin or crater, and a dendritic, tree-like pattern forms on uniform rocks with no structural control.

Answer: A

The key is I is True, II is False: a dam flattens the profile upstream, by deposition, but the erosion below it does not flatten the profile.

Statement I is the standard result. A reservoir slows the river, so its sediment settles where the flow enters the still water, building a delta that raises the bed at the head of the reservoir and lowers its slope. Surveys of reservoirs report steady aggradation and a falling bed slope upstream of the dam, for example on the Niobrara River where it enters Lewis and Clark Lake.

Statement II fails because the water released below a dam is largely stripped of sediment, so it scours the bed and the banks until it regains its load. Repeat surveys below Livingston Dam on the Trinity River in Texas found up to seven metres of incision over forty years that turned an initially straight long profile into a convex-up one, with the deepest lowering nearest the dam. That is a steepening just below the dam rather than a flattening, so II is judged false.

We checked this against river-survey studies, not against a textbook that states the question's wording, so the reading rests on that evidence and on the key. Options B, C and D each need statement II true or statement I false, and statement I is well supported.

Answer: A

The answer is Both I and II are correct.

The thalweg (German for 'valley way') is the line joining the deepest points along a river channel, so statement I is correct. In most alluvial channels the bed alternates between deep pools and shallow riffles, and the thalweg runs through the succession of pools, crossing from side to side in meandering reaches, so statement II is also correct.

That rules out the options marking either statement, or both, as incorrect.

Answer: D

Diluvial theory attributed the shaping of the earth's surface to floods.

Diluvialism (from Latin diluvium, deluge) held that a great flood, usually identified with the biblical flood of Noah, laid down the gravels, erratic boulders and valley forms of the landscape. It was influential among geologists such as William Buckland in the early nineteenth century, before glacial theory explained many of the same deposits.

Glacial theory (Agassiz) and plate tectonics (twentieth century) are later explanations that replaced it, and the nature of the earth's orbit is the basis of Milankovitch's theory of ice-age climate cycles, not of diluvialism.

Answer: A

These ridges are called yardangs.

Yardangs are streamlined ridges of rock or compacted sediment carved by wind abrasion, with a blunt, steep upwind end and a tapering tail, like an upturned boat hull. They line up parallel to the prevailing wind in deserts such as the Lut of Iran and the Taklamakan.

Pediments are gently sloping erosion surfaces at the foot of mountains, inselbergs are isolated residual hills standing above a plain, and buttes (printed 'Buffes') are small flat-topped hills. None of them is a wind-carved streamlined ridge.

Answer: B

It is a wave-cut platform.

Waves undercut the base of a sea cliff, forming a notch. The overhang collapses and the cliff retreats inland, leaving behind a gently seaward-sloping rock surface, a wave-cut platform (shore platform), which is exposed at low tide.

A plateau and a table land are extensive elevated flat areas, not coastal erosion surfaces. Wave base is the depth below which waves no longer disturb the sea floor, about half the wavelength; it is a depth, not a landform.

Answer: A

Both statements are true and the Reason explains the Assertion, so the answer is Both (A) and (R) are true and (R) is the correct explanation of (A).

Long, lofty fold mountain chains such as the Himalaya, the Alps and the Andes rise where plates converge and crust is squeezed. Africa has no chain of that scale; apart from the Atlas in the far northwest, its highlands are old plateaus, block mountains and volcanoes such as Kilimanjaro.

That is because the African plate is bordered mostly by spreading ridges: the Mid-Atlantic Ridge to the west and the ridges of the Indian Ocean to the east and south, with the East African Rift opening inside the continent. Divergent boundaries pull crust apart rather than compress it, so the Reason is the cause of the Assertion, which rules out the options that call either statement false or deny the link.