5.3.1

Question 1

Where 3/4 of volcanoes occur?

Answer 1

Many (about 75%) occur around the ‘Ring of Fire’ surrounding the Pacific Ocean

Question 2

Outline characteristics of volcanic activity at constructive plate margins

Answer 2

At constructive margins, eruptions tend to be small and effusive
The eruptions are usually of basaltic lava:
Low gas content
Low viscosity
Higher temperature

Question 3

Outline characteristics of volcanic activity at destructive margins

Answer 3

At destructive margins, eruptions tend to be explosive as the magma is forcing its way to the surface
These eruptions are often andesitic or rhyolitic lava:
High gas content
High viscosity
Lower temperature

Question 4

Outline how the Volcanic Explosivity Index is measured?

Answer 4

The Volcanic Explosivity Index (VEI) is used to measure the magnitude of an eruption
This is a logarithmic scale from 0-8
It cannot be measured on a scientific instrument so is calculated based on a series of measurements and observations
These include:
Height of material ejected into the atmosphere
Volume of material
Duration of the eruption