Volcanic hazards 2

What are lava flows?

Lava can flow from a volcanic vent down the side of a volcano.

What is the speed and distance of a lava flow like?

Depends on the temperature and viscosity of the lava, as well as the steelhead of the slope.

Low viscosity can flow up to 10km/h on a steep slope, and may travel tens of kilometres.

How quickly do most lava flows move?

Most are relatively slow, so people have time to evacuate areas that will be affected.

How dangerous are lava flows?

They destroy everything in their path, including buildings and vegetation, by burning, burying or knocking it down.

What are volcanic gases?

Lava contains gases such as carbon dioxide and sulfur dioxide, which are released into the atmosphere when a volcano erupts.

What can be said about some of the gases released by eruptions?

Some can be harmful to humans and animals if they're breathed in.

E.g. Sulfur dioxide can create breathing difficulties.

What is pyroclastic fallout?

Material that has been ejected from a volcano during an eruption and calls back down to the ground.

When fallout consists mainly of ash, it’s called ash fallout.

What does fallout consist of?

Materials of a range of sizes - from large pieces of rock weighing several tonnes to microscopic and particles.

How far can ash and pyroclastic fallout travel?

Can travel thousands of metres from the volcano.

Heavier particles are deposited earlier than light ones.

What does heavier material being deposited earlier in fallout mean?

Material ends up well sorted, with larger, heavier particles are deposited near the volcano and smaller, lighter particles (e.g. ash) further away.

What can large pieces of falling tephra do?

Damage buildings and kill or injure people.

What impact can finer material have?

Can form a layer up to several metres in thickness, which can kill vegetation, hinder road and rail transport and cause buildings to collapse.

How can ash be harmful to people?

If it is breathed in.

What are the 2 secondary hazards volcanic eruptions can cause?

• Mudflows (lahars)

• Acid Rain

When do mudflows occur?

When volcanic material mixes with large amounts of water (e.g. from rainfall or from ice melted by the eruption)

How far and how quick can mudflows travel?

Move very quickly (over 80km/h) and can travel for tens of kilometres.

What can mudflows do?

Bury or destroy natural habitats, settlements and infrastructure (e.g. roads and bridges)

What causes acid rain?

Volcanic gases can react with water vapour in the atmosphere, which then falls as acid rain.

e.g. Silver dioxide reacts with water to form sulfuric acid.

What impact can acid rain have?

Can damage ecosystems, and also cause stone and metal to deteriorate, damaging buildings, bridges, statues etc.