With the aid of diagrams, describe the appearance... | WAEC SSCE - Geography - 2008

Question 1 Report

With the aid of diagrams, describe the appearance and mode of formation of any two of the following landforms: \

(a) Delta; (b) block mountain; (c) rock pedestal.

Answer

Appearance and mode of formation of two landforms (any two required):

(a) Delta

Appearance: a low, flat, triangular or fan-shaped plain of alluvium built out at the mouth of a river, split by numerous branching channels called distributaries, with swamps and mud-flats between them. The name comes from the Greek letter delta (\(\Delta\)).
Mode of formation: as a river reaches its mouth its velocity is checked by the standing water of a sea or lake, so it can no longer carry its load. The river deposits its sediment (coarse first, then fine). Where the sea is shallow, tides and currents are weak and the sediment load is large, deposition builds up faster than it can be removed. The deposits accumulate, force the river to divide into distributaries, and gradually extend the land seaward as a delta, for example the Nile and Niger deltas.

(b) Block mountain (horst)

Appearance: an upstanding block of land with steep, often straight fault-scarp sides and a comparatively flat top, standing above the surrounding lowland; adjacent sunken blocks form rift valleys or basins.
Mode of formation: tensional (or compressional) forces in the crust produce parallel faults (lines of fracture). When the land between two faults stands up while the blocks on either side sink, or the central block is pushed up, an upstanding block called a horst or block mountain results. Examples include the Ruwenzori and the Vosges.

(c) Rock pedestal (mushroom rock)

Appearance: an isolated desert rock shaped like a mushroom or table, with a narrow, undercut base (stem) and a broader top.
Mode of formation: in deserts, wind armed with sand grains blasts rock surfaces (abrasion). Because most sand is carried within about a metre of the ground, cutting is strongest near the base. The lower part is worn away faster than the top, and where softer rock lies below harder rock the base is undercut, leaving a narrow stem supporting a wider cap.

Answer Details

Appearance and mode of formation of two landforms (any two required):

(a) Delta

Appearance: a low, flat, triangular or fan-shaped plain of alluvium built out at the mouth of a river, split by numerous branching channels called distributaries, with swamps and mud-flats between them. The name comes from the Greek letter delta (\(\Delta\)).
Mode of formation: as a river reaches its mouth its velocity is checked by the standing water of a sea or lake, so it can no longer carry its load. The river deposits its sediment (coarse first, then fine). Where the sea is shallow, tides and currents are weak and the sediment load is large, deposition builds up faster than it can be removed. The deposits accumulate, force the river to divide into distributaries, and gradually extend the land seaward as a delta, for example the Nile and Niger deltas.

(b) Block mountain (horst)

Appearance: an upstanding block of land with steep, often straight fault-scarp sides and a comparatively flat top, standing above the surrounding lowland; adjacent sunken blocks form rift valleys or basins.
Mode of formation: tensional (or compressional) forces in the crust produce parallel faults (lines of fracture). When the land between two faults stands up while the blocks on either side sink, or the central block is pushed up, an upstanding block called a horst or block mountain results. Examples include the Ruwenzori and the Vosges.

(c) Rock pedestal (mushroom rock)

Appearance: an isolated desert rock shaped like a mushroom or table, with a narrow, undercut base (stem) and a broader top.
Mode of formation: in deserts, wind armed with sand grains blasts rock surfaces (abrasion). Because most sand is carried within about a metre of the ground, cutting is strongest near the base. The lower part is worn away faster than the top, and where softer rock lies below harder rock the base is undercut, leaving a narrow stem supporting a wider cap.

With the aid of diagrams, describe the appearance and mode of formation of any two of the following landforms: \ (a) Delta; (b) block mountain; (c) rock ped...