Volcanic eruptions


Eruption of Mt. Etna, Italy, January 2011 (left, © Flickr/Ivan Iraci) and damage to trees in the area (right, © Flickr/Luca Mondini)

There are approximately 1 500 potentially active volcanoes worldwide, plus hundreds more on the ocean floor. About 500 of these have erupted in historical time. Many of these are located along the Pacific Rim in what is known as the "Ring of Fire".

The intense force of the blast, and the large amount of earth that is either moved or covered with various kinds of debris, makes volcanic eruptions more severe than the hottest fire or the most intense windstorm. Impacts diminish as distance from the volcano increases.

Volcano hazards that may impact forests include:

  • gases, such as sulphur dioxide, carbon dioxide and hydrogen fluoride
  • lahars – volcanic flows composed of hot or cold water and rock fragments
  • landslides
  • lava flows
  • pyroclastic flows – fast-moving currents of hot rock and gas that travel downhill along slope depressions
  • tephra – fragments of volcanic rock and lava that become airborne through explosions or the rise of hot gases. The smallest fragments are volcanic ash.

Young forests are most at risk from ashfall; stands of trees less than two years old are likely to be destroyed by ash deposits thicker than 100 millimetres. Mature trees are unlikely to succumb from ashfall deposition alone, but the accumulated weight of ash can break large branches in cases of heavy ashfall (>500 mm). Defoliation of trees may also occur.

last updated:  Friday, June 28, 2013