Volcanoes and mt nyiragongo

Question 1

What is the spatial distribution of volcanoes?

Answer 1

• clustered around destructive and constructive plate margins, particularly around the ring of fire
• none at conservative margins
• can occur in the centre of plates eg. Hawaiian hotspots and along rift valleys

Question 2

What is a volcano?

Answer 2

• vents in the earth’s crust through which lava, tephra and gases erupt
• when the vents become blocked pressure builds up
• fissures create lower pressure areas that cause rocks to become molten and rise

Question 3

How do different volcano shapes change the characteristics of the materials erupted?

Answer 3

• shield volcanoes are less steep and less viscous lava is more common, they often explode releasing ash
• composite volcanoes are composed of tephra, pyroclastic flows and viscous lava

Question 4

What are the 2 types of lava?

Answer 4

basaltic:
- hot and runny, produces gently sloping landforms and gentle eruptions
- found at constructive margins

andesitic:
- viscous and cooler, violent eruptions due to gas build up
- found at destructive margins

Question 5

How is the magnitude of volcanic eruptions measured?

Answer 5

• using the VEI (volcanic explosivity index), which is a measurement of the volume of erupted materials
• each individual eruption is given a mark on the scale rather than each volcano
• logarithmic scale from 0-8, 8 is very bad

Question 6

What are the advantages and disadvantages of using the VEI?

Question 7

What are the characteristics of composite volcanoes?

Answer 7

• found at destructive margins - very violent eruptions which force bombs out of vents
• very steep-sided, thick and viscous lava

Question 8

What are the characteristics of shield volcanoes?

Answer 8

• basaltic magma
• gentle sided as lava flows long distances before cooling and solidifying
• less violent eruptions

Question 9

What are the secondary impacts of volcanic hazards?

Answer 9

• lahars - melted snow and ice combine with volcanic ash to form mud flows that flow down river valleys at high speeds
• flooding - eruption melts glaciers and ice caps
• landslides - common on volcanic cones because they are tall, steep and weakened by the rise and eruption of molten rock, magma releases gases which dissolve into groundwater and weaken rock, and the thousands of layers of lava leave to faults that can be easily exploited

Question 10

How do volcanoes form at constructive boundaries?

Question 11

How do volcanoes form at destructive boundaries?

Question 12

How do volcanoes form at hotspots?

Question 13

What are the factors affecting the intensity of the effects of volcanic eruptions?

Answer 13

• viscosity of magma - higher viscosity = greater explosivity
• plate margins - more violent eruptions at destructive margins
• materials ejected
• proximity to population centres
• frequency of eruptions and risk perceptions pf population
• prediction

Question 14

How can volcanoes be predicted?

Answer 14

• monitoring seismic activity by looking at shockwaves that result from magma moving towards the surface using seismometers
• monitoring land swelling (using tiltometers), changes in groundwater levels and gas emissions
• overall can be predicted, but difficult to predict when an eruption will actually take place as it can occur very suddenly

Question 15

Where is mount nyiragongo located?

Answer 15

• lies on the eastern border of the democratic republic of the Congo in the Virunga mountains and is associated with the African Rift Valley
• lies 7 miles south of the city of Goma

Question 16

Why did nyiragongo erupt and why were the effects so damaging?

Answer 16

• eruption was caused by tension being released along a series of faults along the East African Rift Valley
• erupted from 3