Vulcanicity
16 Grade 10 Geography questions on Vulcanicity, with worked marking schemes. 16 questions are available on this topic in full.
Question 1
4 marksAccount for the concentration of Kenya's geothermal power stations in the Rift Valley.
(4 marks)
Marking scheme
Any 4 x 1 mark: - The Rift Valley is a zone of crustal weakness where molten rock lies close to the surface, so rocks at shallow depth are extremely hot. - Deep faults and fractures allow surface water to percolate down to these hot rocks. - The water is heated into steam and superheated water, giving a ready supply of the energy required. - Because the hot rocks are shallow, boreholes are comparatively short and drilling is cheaper than it would be elsewhere. - Surface evidence such as hot springs, fumaroles and steam jets at places like Olkaria and Eburru showed engineers exactly where to prospect. - Much of the land there is sparsely settled and of low farming value, so large power fields can be acquired without displacing many people.
Question 2
1 markWhich rock is formed when lava cools very quickly on the earth's surface, giving it extremely fine crystals?
A. Basalt
B. Granite
C. Gneiss
D. Limestone
(1 mark)
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Create a free account to see itQuestion 3
1 markBatian and Nelion, the jagged rocky peaks at the summit of Mount Kenya, are made of hardened lava that once filled the vent of the volcano and was later left standing after the softer materials around it were worn away. This landform is called a
A. volcanic plug
B. cinder cone
C. crater
D. caldera
(1 mark)
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Create a free account to see itQuestion 4
6 marksExplain three ways in which vulcanicity has favoured crop farming in the Kenyan highlands.
(6 marks)
Marking scheme
Any 3 ways, each stated (1 mark) and explained (1 mark) = 6 marks: - Volcanic rocks weather into deep soils rich in plant nutrients, so heavy feeders such as tea and coffee give high yields in areas like Kericho and Kiambu. - Volcanic activity has raised the land to high altitude, giving the cool temperatures needed by tea, pyrethrum and dairy pastures. - The high volcanic mountains force moist air to rise and cool, bringing reliable relief rainfall so crops are grown without irrigation. - Volcanic soils are friable and well drained yet hold enough moisture, making ploughing easier and reducing waterlogging of roots. - The mountains act as water towers feeding permanent rivers whose water is used for irrigating horticultural crops downstream.
Question 5
3 marksDescribe how a sill is formed.
(3 marks)
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Create a free account to see itQuestion 6
1 markWhich intrusive feature is formed when magma solidifies in a vertical crack, cutting across the bedding planes of the surrounding rocks?
A. Laccolith
B. Lopolith
C. Dyke
D. Sill
(1 mark)
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Create a free account to see itQuestion 7
6 marksExplain three factors that determine the shape of a volcanic cone.
(6 marks)
Marking scheme
Any 3 factors, each named (1 mark) and explained (1 mark) = 6 marks: - Nature of the lava: thick, viscous acidic lava hardens close to the vent and piles up into a steep-sided dome, while runny basic lava flows far before solidifying and builds a gently sloping shield cone. - Type of eruption: quiet, steady outpourings spread lava widely to give a low broad cone, whereas explosive eruptions hurl out fragments that pile up steeply around the vent. - Type of material ejected: alternating layers of ash and lava build a tall, well-layered composite cone, while loose cinders alone rest at their steep angle of repose to give a small steep cinder cone. - Number and duration of eruptions: many eruptions over a long period build a large, high cone, while a single short eruption produces only a small one. - Number of vents: eruption through several vents on the flanks produces parasitic cones on the main cone, altering its outline.
Question 8
1 markBoth hot springs and geysers occur along the shores of Lake Bogoria. A geyser differs from a hot spring in that a geyser
A. throws out a jet of hot water and steam at intervals
B. has its water heated by the sun rather than by hot rocks below
C. lets hot water flow out quietly and steadily all the time
D. gives off only steam and volcanic gases and never any water
(1 mark)
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Create a free account to see itQuestion 9
3 marksSuggest three measures a county government could take to reduce the danger to people living near an active volcanic area.
(3 marks)
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Create a free account to see itQuestion 10
1 markIn part of the Rift Valley, a flow of lava has crossed a river valley and hardened right across it. The most likely result of this is
A. the ponding of water behind the lava barrier to form a lake
B. the river flowing faster because its channel has been narrowed
C. the permanent drying up of the river at its source
D. the river sinking underground and never coming to the surface again
(1 mark)
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Create a free account to see itQuestion 11
1 markVulcanicity is best described as the process by which
A. molten rock and gases are forced from the interior of the earth into the crust or onto the earth's surface
B. large blocks of the crust sink downwards along faults to form a rift valley
C. layers of rock in the crust are squeezed by compressional forces into folds
D. rocks lying on the earth's surface are broken down by changes in temperature, water and living things
(1 mark)
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Create a free account to see itQuestion 12
2 marksDistinguish between magma and lava.
(2 marks)
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Create a free account to see itQuestion 13
4 marksDescribe how a caldera is formed.
(4 marks)
Marking scheme
Any 4 x 1 mark: - Magma collects in a chamber beneath a volcanic cone and pressure builds up. - A violent eruption occurs, and a very large volume of magma/lava and pyroclasts is thrown out in a short time. - The magma chamber below the cone is emptied or largely emptied. - The upper part of the cone is left unsupported. - Fractures develop in a roughly circular pattern and the summit collapses (subsides) into the empty chamber. - A very wide, shallow, steep-walled depression, much larger than a crater, is left; this is the caldera, e.g. Menengai in Nakuru. (Accept the alternative route: the top of the cone is blown off by an exceptionally explosive eruption, leaving a wide depression.)
Question 14
3 marksState three ways in which volcanic landforms support the tourism industry in Kenya.
(3 marks)
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Create a free account to see itQuestion 15
1 markWhich one of the following is a way in which vulcanicity has hindered human activities in the areas affected?
A. The high volcanic mountains attract tourists and climbers
B. Volcanic rocks weather into soils that are rich in plant nutrients
C. The rugged volcanic mountains make the building of roads difficult and costly
D. Steam jets are tapped to generate electricity
(1 mark)
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Create a free account to see itQuestion 16
1 markWhich intrusive igneous feature is the largest, being a huge mass of magma that cools slowly deep within the crust and is exposed at the surface only after very long periods of erosion?
A. Batholith
B. Laccolith
C. Phacolith
D. Sill
(1 mark)
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