Volcanic Hazards

Question 1

Types of magma?

Answer 1

Low Viscosity (low silica) Magma
e.g. at divergent plate boundaries
- very runny, so gases can escape easily

High Viscosity (high silica) Magama
e.g. at convergent plate boundaries
- thicker, so harder for gases to escape
Therefore, more/high explosivity

Question 2

Hot spots

Answer 2

Localised heating of the mantle at the core. This creates a mantle plume. The mantle is weakened and rises to the crust, due to partial melting. The magma melts the crust, breaking though, when it reaches the surface active volcanos are formed.

Question 3

Lahars

Answer 3

A lahar is a type of volcanic mudflow.
- A mixture of ash from recent erruption, combined with rainfall, which flows down river valleys.
- This forms a hot, dense, fast-flowing mudflow.

They usually can reach great speeds, travelling up to 45 - 50 mph.
Can be located at any volcano, that has rainfall or even melting snow or ice after.

EXAMPLE - Mount Pinatubo

June 15th 1991
900 killed
-> 100 by Lahars

Within hours if eruption, heavy rainfall began to wash the ash down into the low lands in a fast moving mudflow.

Question 4

Pyroclastic Flows

Answer 4

Very hot (over 800c), gas charged, high velocity flows, made up of a mixture of gas and tephra (volcanic deposit)

Located at compsite volcanoes

Usually flow down the sides of the volcano with record speads of up to 700kmph.

EXAMPLE: Mount Vesuvius

79AD
16,000 deaths
Southern Italy

The blackened clouds of 700*c gas, ash and rock, thundered diwn the slopes of speads of up to 725 kmp, this destroyed all life within Pompeii, buring building, streets and people in a thick layer of debris.

Question 5

Volcanic mitigation

Answer 5

• Having an evacuation plan
  This involves ensuring evacuation stratagies are in place a long with emergency shelter and food suplies.

In Mount Pinatubo, evacuation plans saved many lives with ove 20,000 locals evacuated and surrounding low level populations relocated.