WAEC SSCE - Geography - 2021 (Practical and Physical Geography)
Question 1 Report
Explain how the following factors affect the temperature of a place:
(a) altitudes
(b) distance from the sea
(c) Slope and aspect
How the following factors affect the temperature of a place
(a) Altitude: temperature falls with increasing height above sea level, at an average rate of about 6.5 °C per 1000 m (the normal lapse rate). The air near the ground is warmed from below by the earth's surface, and it is also denser and holds more heat, dust and moisture. Higher up the air is thinner, drier and further from the heated surface, so it loses heat quickly. This is why highland areas such as Jos and mountain tops are cooler than surrounding lowlands on the same latitude.
(b) Distance from the sea (continentality): the sea heats and cools more slowly than the land. Coastal places have a small (moderate) temperature range because the sea warms them in winter and cools them in summer. Places far inland have a large temperature range, with very hot days/summers and cold nights/winters, because land heats and cools rapidly. Sea and land breezes also moderate coastal temperatures.
(c) Slope and aspect: the direction a slope faces (aspect) and its angle control how much insolation it receives. In the northern hemisphere, south-facing slopes face the sun and are warmer, while north-facing slopes are cooler and shaded (the reverse in the southern hemisphere). Slopes at right angles to the sun's rays receive concentrated heat over a small area and become warmer, while gentle or shaded slopes receive slanting rays spread over a wider area and stay cooler.
Answer Details
How the following factors affect the temperature of a place
(a) Altitude: temperature falls with increasing height above sea level, at an average rate of about 6.5 °C per 1000 m (the normal lapse rate). The air near the ground is warmed from below by the earth's surface, and it is also denser and holds more heat, dust and moisture. Higher up the air is thinner, drier and further from the heated surface, so it loses heat quickly. This is why highland areas such as Jos and mountain tops are cooler than surrounding lowlands on the same latitude.
(b) Distance from the sea (continentality): the sea heats and cools more slowly than the land. Coastal places have a small (moderate) temperature range because the sea warms them in winter and cools them in summer. Places far inland have a large temperature range, with very hot days/summers and cold nights/winters, because land heats and cools rapidly. Sea and land breezes also moderate coastal temperatures.
(c) Slope and aspect: the direction a slope faces (aspect) and its angle control how much insolation it receives. In the northern hemisphere, south-facing slopes face the sun and are warmer, while north-facing slopes are cooler and shaded (the reverse in the southern hemisphere). Slopes at right angles to the sun's rays receive concentrated heat over a small area and become warmer, while gentle or shaded slopes receive slanting rays spread over a wider area and stay cooler.
Question 2 Report
(a) List three landforms that are associated with extrusive volcanic action.
(b) With the aid of a diagram, describe the characteristics and mode of formation of laccoliths.
(a) Landforms associated with extrusive volcanic action
- Lava plains or lava plateaux.
- Shield volcanoes (basic lava cones).
- Composite cones (strato-volcanoes).
(b) Laccolith
A laccolith is a concordant intrusive igneous body formed when viscous magma is injected between sedimentary rock beds. It has a nearly flat base and a rounded or dome-shaped upper surface, giving it a mushroom-like form.
Diagram of a laccolith
Characteristics
- It is an intrusive igneous landform, formed below the Earth's surface.
- It lies concordantly, that is, generally parallel to the bedding planes of the surrounding sedimentary rocks.
- It has a broad, almost flat floor and a convex, dome-shaped roof.
- It arches and uplifts the overlying sedimentary strata.
- It is commonly fed from below by a narrow pipe-like conduit or dyke.
- It is composed of hard igneous rock and may stand out as a rounded hill or upland after denudation removes the cover rocks.
Mode of formation
- Viscous magma rises from the interior through a line of weakness or a pipe-like conduit.
- On reaching a resistant rock layer, the magma cannot easily continue vertically upward.
- It therefore spreads sideways along a bedding plane between sedimentary strata.
- Because the magma is thick and does not spread far, it accumulates locally and pushes the overlying beds upward into a dome.
- The magma cools and solidifies beneath the arched strata to form a laccolith.
- Subsequent erosion may remove the overlying sedimentary rocks and expose the resistant laccolith as an upland feature.
Answer Details
(a) Landforms associated with extrusive volcanic action
- Lava plains or lava plateaux.
- Shield volcanoes (basic lava cones).
- Composite cones (strato-volcanoes).
(b) Laccolith
A laccolith is a concordant intrusive igneous body formed when viscous magma is injected between sedimentary rock beds. It has a nearly flat base and a rounded or dome-shaped upper surface, giving it a mushroom-like form.
Diagram of a laccolith
Characteristics
- It is an intrusive igneous landform, formed below the Earth's surface.
- It lies concordantly, that is, generally parallel to the bedding planes of the surrounding sedimentary rocks.
- It has a broad, almost flat floor and a convex, dome-shaped roof.
- It arches and uplifts the overlying sedimentary strata.
- It is commonly fed from below by a narrow pipe-like conduit or dyke.
- It is composed of hard igneous rock and may stand out as a rounded hill or upland after denudation removes the cover rocks.
Mode of formation
- Viscous magma rises from the interior through a line of weakness or a pipe-like conduit.
- On reaching a resistant rock layer, the magma cannot easily continue vertically upward.
- It therefore spreads sideways along a bedding plane between sedimentary strata.
- Because the magma is thick and does not spread far, it accumulates locally and pushes the overlying beds upward into a dome.
- The magma cools and solidifies beneath the arched strata to form a laccolith.
- Subsequent erosion may remove the overlying sedimentary rocks and expose the resistant laccolith as an upland feature.
Question 3 Report
(a) List three landforms associated with coastal erosion.
(b) Explain the following processes of wave erosion:
(i) hydraulic action:
(ii) COrrasion
(a) Three landforms associated with coastal erosion
- Cliffs (and the wave-cut platform at their base).
- Caves, arches and stacks (and stumps).
- Headlands and bays (also blow holes and geos).
(b) Processes of wave erosion
(i) Hydraulic action: this is the erosion caused by the sheer force of moving water. As waves break against a cliff, water is forced into cracks and joints in the rock. The air trapped in these cracks is suddenly compressed and then released as the wave retreats. This repeated compression and expansion weakens and shatters the rock, breaking pieces away. No rock fragments are needed; it is the power of the water and trapped air alone.
(ii) Corrasion (abrasion): this is the wearing away of the coast by the load carried by the waves. Waves pick up sand, pebbles and boulders and hurl them against the cliff face and drag them over the shore platform. This grinding and scraping action, like sandpaper, chips and smooths the rock, deepening notches and enlarging caves.
Answer Details
(a) Three landforms associated with coastal erosion
- Cliffs (and the wave-cut platform at their base).
- Caves, arches and stacks (and stumps).
- Headlands and bays (also blow holes and geos).
(b) Processes of wave erosion
(i) Hydraulic action: this is the erosion caused by the sheer force of moving water. As waves break against a cliff, water is forced into cracks and joints in the rock. The air trapped in these cracks is suddenly compressed and then released as the wave retreats. This repeated compression and expansion weakens and shatters the rock, breaking pieces away. No rock fragments are needed; it is the power of the water and trapped air alone.
(ii) Corrasion (abrasion): this is the wearing away of the coast by the load carried by the waves. Waves pick up sand, pebbles and boulders and hurl them against the cliff face and drag them over the shore platform. This grinding and scraping action, like sandpaper, chips and smooths the rock, deepening notches and enlarging caves.
Question 4 Report
(a) List three types of sedimentary rocks classified according to their mode of formation.
(b) Name the rocks that are formed when the following undergo metamorphism:
(i) granite;
(ii) clay;
(iii) shale;
(iv) limestone
(c) Outline four differences between Sedimentary and metamorphic rocks.
(a) Three types of sedimentary rocks classified by mode of formation
- Mechanically formed (clastic) rocks - from compacted rock fragments, e.g. sandstone, conglomerate, shale.
- Chemically formed rocks - from precipitation of dissolved minerals, e.g. rock salt, gypsum, some limestone.
- Organically formed rocks - from remains of plants and animals, e.g. coal, coral limestone, chalk.
(b) Rocks formed when the following undergo metamorphism
| Original rock | Metamorphic product |
|---|---|
| (i) Granite | Gneiss |
| (ii) Clay | Slate |
| (iii) Shale | Slate (then schist) |
| (iv) Limestone | Marble |
(c) Four differences between Sedimentary and Metamorphic rocks
| Sedimentary rocks | Metamorphic rocks |
|---|---|
| Formed by deposition and compaction of sediments. | Formed by alteration of existing rocks under heat and pressure. |
| Occur in layers or strata (bedded). | Often show banding or foliation, not true bedding. |
| Usually soft and may contain fossils. | Usually hard, crystalline and fossils are destroyed. |
| Formed at or near the earth's surface. | Formed deep within the crust under great heat and pressure. |
Answer Details
(a) Three types of sedimentary rocks classified by mode of formation
- Mechanically formed (clastic) rocks - from compacted rock fragments, e.g. sandstone, conglomerate, shale.
- Chemically formed rocks - from precipitation of dissolved minerals, e.g. rock salt, gypsum, some limestone.
- Organically formed rocks - from remains of plants and animals, e.g. coal, coral limestone, chalk.
(b) Rocks formed when the following undergo metamorphism
| Original rock | Metamorphic product |
|---|---|
| (i) Granite | Gneiss |
| (ii) Clay | Slate |
| (iii) Shale | Slate (then schist) |
| (iv) Limestone | Marble |
(c) Four differences between Sedimentary and Metamorphic rocks
| Sedimentary rocks | Metamorphic rocks |
|---|---|
| Formed by deposition and compaction of sediments. | Formed by alteration of existing rocks under heat and pressure. |
| Occur in layers or strata (bedded). | Often show banding or foliation, not true bedding. |
| Usually soft and may contain fossils. | Usually hard, crystalline and fossils are destroyed. |
| Formed at or near the earth's surface. | Formed deep within the crust under great heat and pressure. |
