volcanoes

Question 1

characteristics of shield volcano

Answer 1

>low-silica  lava
>non-explosive eruptions
>gentle and long slopes
>large area,flat
>broad summits
>1400°C
>formed at divergent plate boundaries

Question 2

characteristics of stratovolcanoe

Answer 2

>high-silica lava
>explosive eruptions
>tall with steep sides
>slightly concave
>gentle base
>900°C
>formed at convergent plate boundaries

Question 3

formation of volcanoes

Answer 3

a volcano is a landform formed by magma ejected from mantle onto earth’s surface

Question 4

vents

Answer 4

opening in earth’s surface with pipe leading to magma chambers

Question 5

secondary vents

Answer 5

during formation of volcanoes,vents may become blocked,preventing the rising of magma and the escape of gases.this causes magma to find a new exit route to surface,forming a secondary lane

Question 6

stratovolcanoe eruption

Answer 6

1. as more magma seeps into the magma chamber,the amount of pressure in chamber builds up,giving rise to a volcanic eruption
2. when a stratovolcano errupts,pyroclasts are released.the force of the volcanic eruption depends on the amount of pressure built up within volcano
3. a new eruption of lava covers the pyroclast and builds up volcano
4. lava builds up around vent,solidifying to form a small volcanic cone known as a crater.
5. during formation of the volcano,the vent may become blocked.this forces magma to find a new exit route to the surface.a secondary cone of newer volcanic material will then develop
6. the sides of a volcano may be blown off during an explosive eruption.the sides of the crater collapse inwards due to lack of structural support.as a result,a large depression known as a caldera is formed

Question 7

lava flows (risks)

Answer 7

lava is erupted during volcanic eruptions.erupted at temperatures between 500°C-1400°C,lava burns the area it flows through and destroys everything in its area.low-silica lava moves rapidly over long distances,causing large areas of damage

Question 8

pyroclastic flows (risks)

Answer 8

pyroclasts are high-density mixtures of hot,dry rock fragments and hot gasses that erupt from vents at high speeds.rock fragments often cause severe damage to properties in areas where they fall. pyroclastic flows can also jam up rivers and cause flooding or mix with water to form lahars

Question 9

mudflow lahars (risks)

Answer 9

formed when pyroclasts mix with water.lahars carrying boulders and logs can crush anything in its path,and buildings may be buried under cement-like layers of rock debris from lahar.

Question 10

ashfalls (risks)

Answer 10

ashfall can travel airborne downwind from a volcano and disrupt human activities.the ashfall may also block sunlight and cause cooling over large areas.when settled on ground,it may suffocate crops and cause respiratory problems for people and animals.

Question 11

fertile soil (benefits)

Answer 11

volcanic soil covers 1% of earth’s surface but supports 10% of world’s population.volcanic soil has fertilising elements that make it richer in nutrients,thus making it favourable for agriculture

Question 12

tourism (benefits)

Answer 12

volcanic areas offer a variety of activities for tourism.many people visit volcanoes to hike or enjoy scenery.this makes volcanic areas a source of income for locals

Question 13

geothermal energy

Answer 13

geothermal energy is derived from heat in earth’s crust.when groundwater comes in contact with hot rocks beneath the surface,it heats up and erupts as hit water or steam.this can be harnessed to drive turbines and produce electricity

Question 14

precious stones and minerals (benefits)

Answer 14

volcanic rocks are rich in precious stones and minerals such as diamond and sulphur.diamonds are useful in industrial tools and in scientific research when refined.they can also be used for jewellery.