Impacts of Volcanic Activity

Question 1

Impacts of Volcanic Activity

Answer 1

A volcanic event can produce a variety of effects, the impact of which can range from the area immediately around the volcano to the whole planet.
The impact presented by a volcanic eruption can be categorised into primary and secondary effects.

Question 2

Primary Effects

Answer 2

Primary effects are brought about by material ejected from the volcano, which include:
- Tephra,
- Pyroclastic flows (nuées ardentes),
- Lava flows,
- Volcanic gases.

Question 3

Tephra

Answer 3

Solid material of varying grain size ranging from volcanic bombs to ash, all ejected into the atmosphere.

Question 4

Pyroclastic Flows (also known as nuées ardentes)

Answer 4

Very hot (over 800°C), gas charged, high-velocity flows made up of a mixture of gas and tephra.
These usually hug the ground and flow down the sides of the volcano with speeds of up to 700 km per hour.
The Roman city of Pompeii (Italy) was destroyed in 79 AD by such flows from Mt Vesuvius.

Question 5

Lava Flows

Answer 5

Lava is a flow of magma that runs down the surface of a volcano.
Lava is a hazard that rarely takes the lives of people.
It flows slowly, giving residents enough time to flee the surrounding area.
However, lava is incredibly destructive, burying, crushing, and burning everything in its path.

Question 6

Volcanic Gases

Answer 6

These include carbon dioxide, carbon monoxide, hydrogen sulphide, sulphur dioxide and chlorine.
In 1986, carbon dioxide emissions from the lake in the crater of Nyos (Cameroon) killed 1,700 people.

Question 7

Secondary Effects

Answer 7

The secondary effects of a volcanic eruption are those that occur in the hours, days and weeks after an eruption. These include:
- Lahars (volcanic mud flows),
- Flooding,
- Volcanic landslides,
- Tsunamis,
- Acid rain,
- Climate change.

Question 8

Lahars (volcanic mud flows)

Answer 8

Melted snow and ice as a result of the eruption combined with volcanic ash forms mud flows that can move down the course of river valleys at high speeds.

In 1985, a lahar destroyed the Colombian town of Armero after an eruption of the volcano Nevado del Ruiz. Only a quarter of the 28,700 population survived.

Question 9

Flooding

Answer 9

When an eruption melts glaciers and ice caps, serious flooding can result.

This happened in Iceland in 1996 when the Grimsvotn volcano erupted.

Question 10

Volcanic Landslides

Answer 10

These are large masses of wet or dry rock and soil that fall, slide, or flow very rapidly under the force of gravity.

Question 11

Tsunamis

Answer 11

Sea waves generated by violent volcanic eruptions such as those formed after the eruption of Krakatoa (Indonesia) in 1883.
Tsunamis from this eruption are estimated to have killed 36,000 people.

Question 12

Acid Rain

Answer 12

Volcanoes emit gases which include sulphur.
When this combines with atmospheric moisture, acid rain results.

Question 13

Climate Change

Answer 13

The ejection of huge amounts of volcanic debris into the atmosphere can reduce global temperatures and is believed to have been an agent in past climate change.

Question 14

Hazardous Volcanic Events

Answer 14

Volcanic events become hazardous when they impact upon people and the built environment, killing and injuring people, burying and collapsing buildings, destroying infrastructure and bringing agricultural and other economic activities to a halt.