WAEC SSCE - Geography - 2021 (Practical and Physical Geography)

(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

(c) Four differences between Sedimentary and Metamorphic rocks

(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.

(a) What is a Great Circle?

A Great Circle is any circle drawn on the surface of the earth whose plane passes through the centre of the earth, thereby dividing the globe into two equal halves (hemispheres). It has the same circumference as the earth. Examples are the Equator and every pair of opposite meridians of longitude.

(b) Three characteristics of a Great Circle

• Its plane passes through the centre of the earth and divides the earth into two equal halves.
• It has the largest circumference possible on the globe, equal to that of the earth.
• The arc of a Great Circle gives the shortest distance between any two points on the earth's surface (used in air and sea navigation).

(c) Time calculation

Given time at 100°E = 5 a.m. on Monday, 11th April 2011. Find values at 10°W.

Difference in longitude \( = 100^\circ + 10^\circ = 110^\circ \).

Since \( 1^\circ = 4 \) minutes of time:

\[ 110 \times 4 = 440 \text{ minutes} = 7 \text{ hours } 20 \text{ minutes} \]

Because 10°W lies west of 100°E, its time is behind, so we subtract:

\[ 5{:}00 \text{ a.m. Monday} - 7\text{h }20\text{m} = 9{:}40 \text{ p.m.} \]

(i) Time at 10°W: 9:40 p.m. (21:40 hours).

(ii) Day at 10°W: Sunday.

(iii) Date at 10°W: 10th April 2011.