(a) What is volcanicity? (b) (i) Apart from a sill, name three other intrusive volcanic features. (ii) Describe how the following features are formed: I a sill; II hot springs; III a caldera. (c) Explain four negative effects of earthquakes.

What is volcanicity?

4/2/2021

KCSE Geography Paper 1 2013 Section B Question 8.

It is the process through which gaseous / liquid / molten rock / solid materials are forced into the earth’s crust and / ejected onto the surface.

I a sill;

Below the earth’s crust the rocks are at very high temperature and high pressure. If the pressure becomes less, the hot, solid rock material may become semi-fluid / Magma under high pressure enters crustal rocks.
The semi-fluid rock / magma forces itself into horizontal cracks/fissures.
The magma cools and solidities in horizontal cracks or bedding plane.
This horizontal sheet/layer of igneous rock is called a sill.

II hot springs;

Rainwater enters the crustal rocks through cracks / fissures.
The water reaches a zone of hot igneous rocks.
The water is (super) heated.
The super heated water changes into water vapour.
The vapour is under high pressure and so forces its way up heating the ground water.
The heated water under pressure flows out continuously/to form hot springs.

III A caldera.

Lava pouring out of a central vent forms a volcanic cone.
The vent may be sealed when lava solidifies in it.
The solidified plug block the gases and steam beneath from escaping.
There is pilling up of pressure below the plug.
The pressure leads to a violent eruption that blows off the top of the cone forming a depression.
The resulting large circular depression on the top of the (now lower) volcano is called caldera.

OR
A subsidence caldera

Lava pouring out of a central vent forms a volcanic cone.
The magma resevoir below the crust is left empty/has a void/cavity.
With time the weight of rocks of the volcano exerts pressure on the crustal rocks below.
The pressure/earth movements cause cracks to develop making the volcano unstable.
Over time the middle portion of the volcano subsides/collapses into the void forming a depression.
The resulting large circular depression on the top of the (now lower) volcano is called caldera.

OR
Outward collapsing

Volcanic eruption of ash and cinder/pyroclasts through a central vent forms a volcanic cone.
Several eruptions results to a high, steep and unstable volcano.
The weight of the upper materials exerts pressure on the ones beneath causing instability on the lower part.
The material at the base begin spreading outwards.
The top of the volcano collapses inwards forming a depression.
The resulting large circular depression on the top of the volcano is called caldera.

Violent motions resulting from earthquakes damage structures from their foundations leading to loss of life and property.
When earthquakes occur faults may develop which damages infrastructure.
During an earthquake on the sea floor vertical displacement occur leading to development of tsunami leading to floods of coastal areas/disrupts human activities loss of life/property.
Earthquakes may lead to landslides which destroy agricultural land/loss of life/damage of infrastructure..
Strong vibrations from earthquakes may cause damage to nuclear plants which pollute the environment and affect human health.
Earthquakes may cause panic/emotional shock/fear.