Volcanic Activity

Question 1

basic explanation to volcanoes formation

Answer 1

• high pressure inside earth keeps parts of mantle semi-molten
• when pressure is released, rocks become molten, hot molten rock is magma
• magma is less dense than rock around it, so rises up to earth’s surface

Question 2

what is intrusive volcanic activity?

Answer 2

• takes place beneath the earth’s surface

- includes formation of large magma chambers and magma being forced into the crust through cracks in the rock

Question 3

what is extrusive volcanic activity?

Answer 3

• takes place on the earth’s surface
• major form of this activity is volcanic eruptions of lava
• minor types of extrusive volcanic activity include hot springs, geysers, and boiling mud pools

Question 4

what three things does intrusive volcanic activity form?

Answer 4

dykes, sills and batholiths

Question 5

how does a batholith occur?

Answer 5

when large chambers of magma cools underground they form domes of igneous rock called batholiths

Question 6

how do dykes occur?

Answer 6

where the magma has flowed into gaps in the surrounding rock and cooled it forms vertical dykes going across the layers of rock

Question 7

how do sills occur?

Answer 7

where magma has flowed into gaps in the surrounding rock and cooled it forms horizontal sills going between the layers of rock

Question 8

what are cooling cracks?

Answer 8

cracks that form when magma cools

they’re vertical in sills and horizontal in dykes

Question 9

what are the 3 main types of lava? and what plate margins do they occur at?

Answer 9

• basaltic lava - constructive PM
• andesitic lava - destructive PM
• rhyolitic lava - destructive PM

Question 10

what are the characteristics of basaltic lava?

Answer 10

• low silica content
• low viscosity (runny) - flows easily, gas can escape
• over 950oC
• eruptions aren’t violent, erupt frequently for long periods of time

Question 11

what are the characteristics of andesitic lava?

Answer 11

• medium silica content
• medium viscosity, can forms blockages in vents
• 750-950oC
• pressure builds in blocked vents until released and creates violent volcano

Question 12

what are the characteristics of rhyolitic lava?

Answer 12

• high silica content
• high viscosity (thick and sticky), flows less easily, forms blockages in vents
• less than 750oC
• pressure builds in blocked vents until released and creates violent volcano

Question 13

what are the 4 type of volcano?

Answer 13

• dome
• caldera
• shield
• fissure

Question 14

what are the characteristics of a dome volcano?

Answer 14

• layers of lava
• steep sides - caused by high viscosity lava flowing for short distances
• central vent
• rhyolitic or andesitic lava

Question 15

where do dome volcanoes occur? example?

Answer 15

destructive plate margins e.g. Puy de Dome in France

Question 16

what are the characteristics of a caldera?

Answer 16

• very wide circular crater, can be several km across
• central part of volcano has collapsed
• layers of lava or layers of lava, ash and cinders
• andesitic and rhyolitic lava

Question 17

where do calderas occur? example?

Answer 17

destructive plate margins e.g. Aira Caldera in Japan

Question 18

what are the characteristics of a shield volcano?

Answer 18

• layers of lava
• gently sloping sides - caused by low viscosity lava flowing for long distances
• central vent
• basaltic lava

Question 19

where do shield volcanoes occur? example?

Answer 19

constructive margins e.g. Mauna Loa in Hawaii

Question 20

what are the characteristics of a fissure volcano?

Answer 20

• layer of lava
• long, linear vent - few metres wide but several km long
• fairly flat surface caused by low viscosity lava flowing for long distances
• basaltic lava

Question 21

where to fissure volcanoes occur? example?

Answer 21

constructive margins e.g. Laki Fissure System in Iceland

Question 22

how does a hot spring occur?

Answer 22

if groundwater source of a spring flows close to an area of recent intrusive volcanic activity, the water is heated and so the spring becomes hot

Question 23

what are the temperatures of a hot spring?

Answer 23

between 20oC and 90oC

Question 24

example of hot spring

Answer 24

North Island, New Zealand

Question 25

what are geysers?

Answer 25

a type of hot spring where hot water and steam are ejected from the surface in a fountain, form in areas of intense volcanic activity

Question 26

what does a geyser occur?

Answer 26

• groundwater is heated to above boiling point by magma deep in the crust
• hot water becomes pressurised and forces its way to the surface along cracks in rocks
• hot water and steam spray out from a vent

Question 27

how often do geysers erupt

Answer 27

erupt periodically because they only erupt when the pressure has built up enough to force the water out of the ground

Question 28

example of a geyser?

Answer 28

Old Faithful in Yellowstone National Park

Question 29

what is a boiling mud pool?

Answer 29

a pool of boiling mud, another type of hot spring

Question 30

where do boiling mud pools occur?

Answer 30

form in areas with very fine-grained soil (e.g. soil rich in clay or volcanic ash)

Question 31

what is a hot spot?

Answer 31

a volcano that occurs away from a plate margin

Question 32

what causes a hot spot?

Answer 32

caused by a magma plume - a vertical column of magma that rises up from the mantle

Question 33

how is a hot spot formed?

Answer 33

• volcanoes form above magma plumes
• magma plume remains stationary over time, but the crust moves above it
• volcanic activity in the part of the crust that was above the hotspot decreases as it moves away
• new volcanoes form in the part of the crust that is now above the hot spot
• as the crust continues to move, a chain of volcanoes is formed
  e. g. Hawaii