WAEC SSCE - Geography - 2016 (Practical and Physical Geography)

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(a) Three differences between plutonic and volcanic rocks

(b) Mode of formation of a crater lake

A crater lake is a body of water that collects in the crater or caldera of a volcano.

• During a volcanic eruption, lava, gases and pyroclastic materials are ejected through a central vent, leaving a funnel-shaped hollow called a crater at the top of the volcanic cone.
• When the volcano becomes dormant or extinct, eruption ceases and the vent is sealed by cooled, solidified lava which makes the crater floor fairly water-tight.
• Over time, rainfall and sometimes underground water collect in the enclosed crater because there is no easy outlet.
• The accumulated water fills the depression to form a roughly circular crater lake. Where a very large collapse depression (caldera) is filled, a larger caldera lake is formed.

A well-labelled diagram should show the volcanic cone, the crater/vent, the solidified plug of lava at the base, and the water accumulated in the crater.

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(a) Definition of climate

Climate is the average weather conditions of a place taken over a long period of time, usually not less than 35 years. It describes the general or expected atmospheric conditions (temperature, rainfall, pressure, humidity, wind, sunshine) of an area rather than the day-to-day changes.

(b) Instruments used to measure the climate elements

(c) Four ways the study of weather and climate is important to man

• Agriculture: It guides farmers on the right time to plant, apply fertiliser and harvest crops.
• Aviation and shipping: Weather forecasts help pilots and sailors to plan safe journeys and avoid storms.
• Disaster prediction: It gives early warning of floods, droughts and storms, allowing people to take precautions.
• Planning of daily activities and clothing: It helps people decide on appropriate clothing, building design and outdoor activities.
• Tourism and health: It helps in planning tourism and in understanding the spread of climate-related diseases.

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(a) Three characteristics of a limestone (karst) region

• The surface is dry, with few surface streams because water sinks quickly through the permeable, well-jointed rock.
• The land shows underground drainage, with caves, caverns and disappearing streams (swallow holes/sink holes).
• Surface features such as clints and grikes (limestone pavements), dolines and dry valleys are common.
• Soils are thin and rocky, so the region is generally poor for agriculture.

(b) Formation of a limestone pillar

A limestone pillar (column) forms inside a cave by the joining of a stalactite and a stalagmite.

• Rainwater absorbs carbon dioxide from the air and soil to form a weak carbonic acid.
• This acidified water seeps through joints and cracks in the limestone and dissolves the calcium carbonate, carrying it in solution into the cave.
• When a drop of this water hangs from the cave roof, some water evaporates and a little calcium carbonate is deposited. Repeated dripping builds a downward-growing icicle-like feature called a stalactite.
• Water dripping onto the cave floor also deposits calcium carbonate, building an upward-growing feature called a stalagmite.
• Over a very long time the stalactite and stalagmite grow towards each other and eventually join to form a continuous limestone pillar (column).

(c) Two ways limestone is important to man

• It is used as a major raw material for the manufacture of cement.
• It is used in building (as building stone) and in the iron and steel industry as a flux, and can be used to make lime for agriculture.

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(a) Three differences between deflation and abrasion

(b) Mode of formation of a deflation hollow

A deflation hollow is a shallow depression on the desert floor produced by wind deflation.

• In arid regions the surface is covered with loose, dry, unconsolidated sand and dust particles that are not held together by moisture or vegetation.
• Strong winds blowing over the surface pick up and carry away these fine, loose particles in a process called deflation.
• As the loose material is continually removed, the ground level is progressively lowered and a depression begins to form.
• Deflation continues until the wind reaches the water table (where the sand becomes damp and can no longer be lifted) or a layer of coarse pebbles too heavy to move, forming a desert pavement. At this point deepening stops.
• The resulting shallow, enclosed depression is the deflation hollow. A well-known example is the Qattara Depression in Egypt.

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(a)(i) Definition of the solar system

The solar system is the system made up of the Sun and all the heavenly bodies, such as the planets, their moons (satellites), asteroids, comets and meteors, that move round (revolve about) the Sun under the influence of the Sun's gravitational pull.

(ii) Five components of the solar system

• The Sun
• The planets (for example Earth, Mars, Jupiter)
• Satellites (moons)
• Asteroids (minor planets)
• Comets
• Meteors and meteoroids

(b) Four characteristics of the earth

• It is the third planet from the Sun and is almost spherical (an oblate spheroid, slightly flattened at the poles and bulging at the equator).
• It is the only planet known to support life, because it has the right temperature, water and an atmosphere containing oxygen.
• It rotates on its axis once in about 24 hours (causing day and night) and revolves round the Sun once in about 365 and a quarter days (causing the seasons).
• It has one natural satellite, the Moon, which revolves round it.
• About 71 per cent of its surface is covered by water and 29 per cent by land.

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(a)(i) Two ways in which water resources are classified

• According to source/location: surface water (rivers, lakes, seas) and underground water (springs, wells, aquifers).
• According to salt content: fresh water (rivers, lakes) and salt water (seas and oceans).

(ii) Three ways water resources can be used

• For domestic use (drinking, cooking, washing).
• For agriculture, especially irrigation and watering of livestock.
• For industrial use, for the generation of hydro-electric power, and for transportation and fishing.

(b) Three ways in which man's activities limit the use of water as a resource

• Pollution: The discharge of industrial waste, sewage and oil spillage into rivers and seas makes the water unfit for drinking and harmful to aquatic life.
• Deforestation and poor farming: Clearing of vegetation and bad farming practices increase runoff and silting, which reduce the volume and quality of water in rivers and reservoirs.
• Over-abstraction and damming: Excessive withdrawal of water and the building of dams upstream reduce the amount of water available to downstream users, sometimes drying up rivers and lowering the water table.