Geomorphology Questions and Answers

Answer: B

Unsorted material accumulated along the margins of a valley glacier forms a lateral moraine.

Rock debris falls from the valley walls onto the edges of the glacier and is also scraped from the sides. It is carried along the margins and left as ridges of till along the valley sides when the ice melts.

Ground moraine is till spread as a sheet beneath the glacier. Terminal and end moraines are ridges formed at the snout of the glacier, marking the farthest advance (terminal) or a halt during retreat, not along its sides.

Answer: C

Aggradation leads to raising of the stream channel elevation.

Aggradation is the building up of a channel bed and floodplain by deposition of sediment, which happens when a river receives more load than it can carry, for example below a glacier or where its slope decreases. The bed level rises over time.

Lowering of channel elevation and deepening of the channel are the effects of degradation, the opposite process. Aggradation tends to steepen, not reduce, the slope of a channel, until it can carry its load again.

Answer: B

The peeling away of layers or sheets of rock is exfoliation.

Exfoliation (onion-skin weathering, or sheeting on a larger scale) occurs when outer layers of rock expand and split off in curved sheets, owing to unloading as overlying rock is removed, daily heating and cooling, or chemical weathering along the surface. Granite domes such as Half Dome are classic examples.

Exhumation is the uncovering of buried rock by erosion, insolation is the heating of the surface by the sun (one possible cause of exfoliation), and chelation is a chemical weathering process involving organic compounds.

Answer: C

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

• Pools alternate with riffles along a stream channel: deep, slow stretches with shallow, fast ones (a-3).
• Sapping is erosion by groundwater seeping out at the base of a slope, which undermines it and lengthens the valley headward (b-4).
• A barrier spit encloses a lagoon behind it (c-1).
• A stack is left standing off a headland when an arch collapses (d-2).

The other codes pair pools with lagoons or headlands and sapping with riffles, which do not belong together.

Answer: D

Solifluction is a slow flow type of mass movement.

In solifluction, waterlogged soil and regolith flow slowly downslope, typically a few centimetres to a metre a year. It is most common in periglacial regions, where a thawed surface layer saturated with meltwater moves over frozen ground that stops the water draining away. It produces lobes and terraces on the slopes.

It is not a slide, because the material deforms internally rather than moving as a block along a slip surface. It is not a rapid flow such as a mudflow or debris avalanche, and it is not subsidence, which is the vertical sinking of the ground.

Answer: B

Uniformitarianism was popularised by C. Lyell.

Charles Lyell's Principles of Geology (three volumes, 1830-33) argued that the earth's features were shaped by the same slow processes that operate today, acting over immense time. The idea, summed up as 'the present is the key to the past', had been proposed earlier by James Hutton, but it was Lyell's book that made it the foundation of modern geology and geomorphology.

Hutton is the near miss: he originated the principle in the 1780s but did not write Principles of Geology. Walther Penck is known for his model of slope development, and Alfred Wegener (printed 'Wegner') for continental drift.

Answer: D

A scroll lake is a riverine feature.

On the floodplain of a meandering river, the inner bank of each bend builds out as a series of curved ridges called meander scrolls or scroll bars. The low swales between those ridges hold water as narrow, curved scroll lakes, so they belong to the depositional landforms of rivers, alongside ox-bow lakes and levees.

A playa is a shallow lake in a desert basin, karstic lakes form in solution hollows in limestone, and glacial meltwater lakes such as kettle lakes and tarns form in glaciated terrain. None of these is built by a meandering river.

Answer: D

Paternoster lakes are a glacial feature.

A glacier eroding its valley deepens it unevenly, scouring out a series of rock basins where the rock is weaker or the ice was more erosive, separated by rock steps. When the ice melts these basins fill with water, giving a chain of small lakes down the U-shaped valley, likened to the beads of a rosary (the paternoster).

Riverine lakes include ox-bow and scroll lakes, aeolian processes make deflation hollows, and karstic lakes form in limestone solution features such as poljes and dolines. None gives a chain of rock basins along a valley.

Answer: A

Ventifacts are shaped by the abrasive action of wind.

A ventifact is a stone cut, faceted and often polished by wind-blown sand. The sand grains act like a sandblaster: wind abrasion wears away the exposed face of the rock, and a change in wind direction or a shift in the stone's position produces several flat facets meeting at sharp edges.

Deflation is the removal of loose particles by the wind, which lowers the surface but does not cut stones. Attrition is the wearing down of the moving grains themselves as they collide. Corrosion means chemical solution, a process of water, not of wind.

Answer: C

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

• Geosynclinal theory (Hall, Dana, Kober): mountain building from sediments in long troughs.
• Tetrahedral hypothesis (Lowthian Green): the origin of continents and ocean basins on a shrinking, tetrahedron-shaped earth.
• Stationary wave theory (R.A. Harris): the origin of tides, as standing oscillations in ocean basins.
• Subsidence theory (Darwin): the origin of coral reefs and atolls on slowly sinking islands.

The option with c-2 and d-1 swaps tides and coral reefs, and the options with a-4 give continents to the geosynclinal theory instead of mountain building.