2. What types of volcanic eruptions exist ?

Volcanic eruptions occur in areas where volcanoes are still active and where there are human settlements and activities. Simply speaking a volcano is described as active if it erupted:

  • in historical times: if its activity is described by historical documents;
  • in Holocene time: if its activity is not described by documents but scientific analysis indicates activity in the last 10,000 years.

Active volcanoes can be broadly divided into two main types:

Effusive Volcanoes

They bring about hazards as slowly moving lava flows, little explosions, ground deformations, lava fountains, gas and steam emissions.

Etna (Italy)
Etna (Italy)
Manua Loa (Hawaii)

Explosive volcanoes

They bring about large explosions which can partially destroy the volcano, high columns of rock materials (rock debris, rock blocks, ash, steam, etc.) projected in the atmosphere and subsequently falling down along the sides of the volcano, as well as lava flows, mud and debris flows along the sides of the volcano, earthquakes and noxious gas emission. The explosivity of an eruption usually results from gases expanding within a viscous lava or from water entering a magma chamber or channel. These eruptions are possible when a volcano is located in areas with large underground water reservoirs, in the sea or in lakes.

Source: "The Eruption of Vesuvius as seen from Naples, October 1822" from V. Day & Son. In G. Julius Poulett Scrope, Masson, 1864. Historical Draw from George Julius Poulett Scrope (1797-1876)
St. Helens (USA). Credits: photo by United States Air Force

Credit: U.S. Geological Survey. Department of the Interior, USA