The diagram below shows some intrusive features formed by vulcanicity. Use it to answer question (a)

KCSE Geography Paper 1 2004 Section B Question 9.

​The diagram below shows some intrusive features formed by vulcanicity. Use it to answer question (a)

​a) i) Name features marked X,Y, and Z 

• X – Laccolith
• Y-Batholith
• Z –Dyke

​ii) Explain how a sill is formed 

• Rocks beneath the crust are in a semi –solid state due to high temperature and high pressure.
• When pressure decreases the rocks become semi- fluid and are known as magma.
• Earth movements cause vertical or horizontal cracks in the rocks
• The molten rock / magma forces itself through the cracks / fissures.
• When magma cools and solidifies in a horizontal crack or bedding plane it forms a feature called a sill.

​b) Describe the characteristics of a composite volcano 

• It has a vertical vent or pipe
•  It is composed of alternating layers of ash / and lave
•  It is conical in shape / steep sided
•  It has a side vents
•  It has conelets / parasitic cones on the sides
•  At the peak it may have a caldera / crater / plug

​c) Explain four ways in which volcanic mountains positively influence human activities. 

• Volcanic mountains are sources of rivers which provide water from domestic, industrial, transport and irrigation.
• They influence the formation of relief rainfall that encourages agricultural     activities.
• Volcanic soils are suitable for agriculture.
• Timber for construction / building industries
• The volcanic mountains form beautiful sceneries that attract tourists.
• Hot springs / geysers are used to generate geothermal
• The crater laters are fishing / breeding grounds for fish.
• Volcanic rocks provides materials for construction / buildings.

d) Students carried a field study on volcanic rocks
i) Give four reasons why it is necessary to collect rock samples during such a field study. ​

• There is no field laboratory where the rock samples can be analyzed.
• Students do not have adequate skills to analyze the samples so there is need for expert opinion.
• There is no adequate time in the field
• To enable them build a collection of rock samples / future studies
• It would expose more students to their findings through display of their findings.
• To create interest / motivation and to deepen the understanding of the subject.

​ii) State two problems they are likely to have experienced during the field study

• Some students may have been cut / injured by the rocks
• There may have been harsh weather / weather change.
• Inability to collect the right samples.
• Inaccessibility of some sample sites
• The heavy weight of the rock samples

​Related Geography Searches on Internal land forming processes, Volcanicity Form 2 Level

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