tectonics L3 Volcanoes

Question 1

What causes volcanic eruptions?

Answer 1

• destructive boundaries — subducted plate heats up and loses its water (& sulphur) which enters the mantle, lowering the melting temperature of mantle rocks and produces magma — not all can be dissolved by magma so gas bubbles produced, increases magmastatic pressure.
• constructive boundaries - plates moving apart creates a crack & pressure is lowered, lowers melting temperature of mantle rocks, magma then erupts

Question 2

How do we measure the magnitude of volcanic eruptions?

Answer 2

classified on a logarithmic scale called the Volcanic Explosivity Index (VEI)
scaled from 0-8 — volume and height of ejected material, duration of eruption, qualitative descriptive terms

Question 3

EFFUSIVE eruptions

Answer 3

• occur when magma has low silica content & therefore low viscosity
• gas emissions from larger eruptions can affect climate
• form shield volcanoes - large, round, low lying structures
• do NOT produce ash
• constructive boundary or middle of plates.

Question 4

EXPLOSIVE eruptions

Answer 4

• high silica & gas content — high viscosity
• very hazardous, produce ash, pyroclastic flow & lahars.
• create composite volcanoes - repeated layers of ash and lava over multiple eruptions
• destructive boundaries

Question 5

Primary Hazards of Volcanic Eruptions

Answer 5

lava
ash
tephra
pyroclastic flow
gas
crustal fracturing

Question 6

Can we PREDICT eruptions?

Answer 6

all methods are designed to detect magma movement
- rising magma can cause ground deformation — parts of volcano bulge or recede.
— global positioning systems and tilt metres can both pick up changes in ground level (measure angle of slope on a volcanoes flank)

• movements underground can cause minor earthquakes as space is made to accommodate new material
  — seismometers measure earthquakes
• all magma contains gas — when it rises the pressure decreases allowing more gas to escape
  — measure changes in gas emissions at volcanic vents, volcanologists can tell from this when magma has risen.

Question 7

secondary impacts of volcanic eruptions/also earthquakes kind of

Answer 7

climate change
tsunami
landslide/rockfall
lahar
jokulhlaup
liquefaction