Chapter 3: Dryland landscapes - OCR A-Level
Geography Questions and Answers
Surface wash ✔️✔️The process which occurs when infiltration capacity is exceeded or saturation
is reached. Gullies are sometimes formed. Also occurs when ground is frozen.
Infiltration capacity ✔️✔️The maximum rate at which rain can be absorbed by a soil in a given
condition.
Erosional desert landforms ✔️✔️-Wadis
-Canyons
-Pedestal rocks
-Ventifacts
-Desert pavements
Erosional desert landforms definition ✔️✔️The erosional processes operating in mid- and low-
latitude deserts give rise to distinctive landforms. Among these desert landforms are wadis,
canyons, pedestal rocks, ventifacts and desert pavements.
Wadis (Erosional desert landforms) ✔️✔️Wadis are stream and river channels which are dry for
most of the time. Although run-off in deserts is short lived, temporary streams and rivers have
abundant surplus energy for erosion. This is partly due to the nature of the rainfall, which is
often convective and intense; and to rapid run-off and high peak flows.
Rapid run-off is due to limited water storage because of minimal soil and vegetation cover, and
ground surfaces baked hard by the Sun. The result is powerful flash floods.
Wadis (Erosional desert landforms) (Diagram) ✔️✔️
Convective ✔️✔️Surface air that is heated and, thus, is rising
, Canyons (Erosional desert landforms) ✔️✔️Canyons are narrow river valleys with near vertical
sides, cut into solid rock. They are a common feature of desert mountains and plateaux and
evidence of the power of fluvial erosion are formed by the scouring action of coarse sediment
transported by rivers.
The shape of canyons in cross profile is mainly determined by rock type. Where rocks are highly
resistant and homogeneous, narrow slot canyons with vertical rock walls develop. Antelope
Canyon, near Page in Arizona, is a classic example. Other canyons (including the Grand Canyon)
where rocks of variable resistance crop out have stair-like sides.
Canyons (Erosional desert landforms) (Processes) ✔️✔️Erosion is vertical rather than lateral
because
1. Solid rock walls allow little sideways movement of river channels
2. Mass movements processes which would lower valley slopes in more humid environments
(e.g. soil creep, mudlows, landslides), are absent in deserts. deserts. Canyons
Canyons (Erosional desert landforms) (Diagram) ✔️✔️
Pedestal rocks (Erosional desert landforms) ✔️✔️Pedestal rocks are isolated, mushroom-shaped
rocks which belong to a larger group of wind-eroded rocks known as zeugens. Their curious
shape is explained by the undercutting erosive effects of saltating sand grains confined to
within 1.5 m of the ground.
This process may be aided by weathering concentrated at the base of rocks where moisture is
more freely available.
Sometimes called hoodoo rocks.
Pedestal rocks (Erosional desert landforms) (Diagram) ✔️✔️
Geography Questions and Answers
Surface wash ✔️✔️The process which occurs when infiltration capacity is exceeded or saturation
is reached. Gullies are sometimes formed. Also occurs when ground is frozen.
Infiltration capacity ✔️✔️The maximum rate at which rain can be absorbed by a soil in a given
condition.
Erosional desert landforms ✔️✔️-Wadis
-Canyons
-Pedestal rocks
-Ventifacts
-Desert pavements
Erosional desert landforms definition ✔️✔️The erosional processes operating in mid- and low-
latitude deserts give rise to distinctive landforms. Among these desert landforms are wadis,
canyons, pedestal rocks, ventifacts and desert pavements.
Wadis (Erosional desert landforms) ✔️✔️Wadis are stream and river channels which are dry for
most of the time. Although run-off in deserts is short lived, temporary streams and rivers have
abundant surplus energy for erosion. This is partly due to the nature of the rainfall, which is
often convective and intense; and to rapid run-off and high peak flows.
Rapid run-off is due to limited water storage because of minimal soil and vegetation cover, and
ground surfaces baked hard by the Sun. The result is powerful flash floods.
Wadis (Erosional desert landforms) (Diagram) ✔️✔️
Convective ✔️✔️Surface air that is heated and, thus, is rising
, Canyons (Erosional desert landforms) ✔️✔️Canyons are narrow river valleys with near vertical
sides, cut into solid rock. They are a common feature of desert mountains and plateaux and
evidence of the power of fluvial erosion are formed by the scouring action of coarse sediment
transported by rivers.
The shape of canyons in cross profile is mainly determined by rock type. Where rocks are highly
resistant and homogeneous, narrow slot canyons with vertical rock walls develop. Antelope
Canyon, near Page in Arizona, is a classic example. Other canyons (including the Grand Canyon)
where rocks of variable resistance crop out have stair-like sides.
Canyons (Erosional desert landforms) (Processes) ✔️✔️Erosion is vertical rather than lateral
because
1. Solid rock walls allow little sideways movement of river channels
2. Mass movements processes which would lower valley slopes in more humid environments
(e.g. soil creep, mudlows, landslides), are absent in deserts. deserts. Canyons
Canyons (Erosional desert landforms) (Diagram) ✔️✔️
Pedestal rocks (Erosional desert landforms) ✔️✔️Pedestal rocks are isolated, mushroom-shaped
rocks which belong to a larger group of wind-eroded rocks known as zeugens. Their curious
shape is explained by the undercutting erosive effects of saltating sand grains confined to
within 1.5 m of the ground.
This process may be aided by weathering concentrated at the base of rocks where moisture is
more freely available.
Sometimes called hoodoo rocks.
Pedestal rocks (Erosional desert landforms) (Diagram) ✔️✔️
