1st ESO

3rd ESO

4th ESO

Biology 2nd Baccalaureate

Index by courses



Skip navigation

15.2.2. Volcanic risk

Volcanic risk

The volcanic risk is the expectation that the eruption of a volcano produces a negative impact on humans. Like all risks, it is a function of three factors:

  • Dangerousness: Probability that the volcanic eruption will occur in a place, in a given time.
  • Exposure: Value of assets that can be lost if the eruption occurs.
  • Vulnerability: Percentage of loss that the exposed assets will suffer in the event of the event, in this case, the volcanic eruption.

Volcanic activity can cause damage by the following direct risks:

  • Lava flows. They can destroy infrastructure and populations. The risk is greater the more viscous (less fluid) the lava is.
  • Burning clouds. In very viscous magmas, with a lot of silica, gases and ashes are expelled at great temperature and speed.
  • Pyroclastic fall. Bombs, lapilli and ash fall from the eruptive column. It occurs in explosive volcanoes, with acid magma .
  • Toxic gases. Many volcanic gases are toxic, such as carbon monoxide (CO) and hydrochloric acid (ClH).

 There may also be other indirect risks:

  • Lahars. They are mud flows that go down the slopes of the volcano produced by different causes, such as torrential rains, collapse of the slopes of the volcano, or by melting of the snow that covers the volcano when it erupts. This happened in 1985, when the eruption of the Nevado del Ruiz volcano caused a stream of mud that buried Armero ( Colombia ) and 25,000 people died.
  • Tsunamis. Giant waves produced as a result of a volcanic eruption (or a tsunami) .
  • Magma movements can produce earthquakes.
  • Other hazards, such as fire, hillside movements, etc.

To avoid these volcanic risks we can take a series of measures:

Prediction measures

Some of the predictive measures are:

  • Know the return period to know the frequency of the eruptions.
  • Detect small tremors, noises, changes in topography, anomalies in gravity, change in gases emitted, etc., which may indicate an upcoming eruption.
  • Preparation of hazard and risk maps to determine the possible activities in each area.

Prevention measures

Some preventive measures can be:

  • Divert lava flows to uninhabited places.
  • Avoid the formation of lahars by extracting the water from the crater lakes.
  • Evacuation of the population if there is risk.
  • Contracting of insurance that covers the loss of property.
  • Avoid construction in the areas of greatest risk .
  • Alarm systems that warn the population of a possible risk.
  • Construction of houses with very sloping or hemispherical roofs that prevent volcanic ash from being deposited on top and sinking them.
  • Construction of fireproof shelters to protect against fiery clouds.


Legal warning






Follow us if it has been useful to you

Biology and Geology teaching materials for Compulsory Secondary Education (ESO) and Baccalaureate students.