Volcanoes

Draw a stratovolcano.

Draw a shield volcano.

The amount of silica in magma will affect the viscosity of the magma. Select the following options which are true.

• This affects how easy gas escapes, and the amount of pressure which builds up.

• This affects the explosiveness of eruption.

• This affects the speed of lava after eruption and the distance lava can travel before cooling.

• This affects the shape of the volcano.

What criteria does the Volcanic Explosivity Index (VEI) use?

• Volume of ejected material

• Height of eruption cloud

• Duration of eruption

• Type of magma produced

Explain for the formation of a stratovolcano.

Answer explanation

High viscosity magma rises through weak areas in the crust to the Earth’s surface and erupts explosively as lava, ash and rocks

The ash and rocks settle on the sides of the volcano, and are later covered by lava

Over successive eruptions, a tall volcano consisting of alternating layers of ash and lava develops

As the highly viscous lava travels a shorter distance before cooling and solidifying, the volcano has steep sides and a narrow summit

Explain for the formation of a shield volcano.

Answer explanation

Low viscosity magma rises through weak areas in the crust to the Earth’s surface and erupts effusively

Over successive eruptions, a volcano consisting of layers of lava develops

As the less viscous lava travels a longer distance before cooling and solidifying, the volcano has gentle sloping sides with a broad summit