Phreatomagmatic Eruption



A new island has emerged near Japan’s Ogasawara island chain following an underwater volcano eruption in late October 2023.


Phreatomagmatic Eruption

A phreatomagmatic eruption, also known as a hydrovolcanic eruption or a steam-blast eruption, is a type of volcanic eruption that occurs when magma comes into contact with water. The water can be groundwater, surface water, or even snow or ice. When the water is heated by the magma, it vaporizes rapidly, creating a large amount of steam. This steam pressure can then build up and eventually explode, creating a powerful eruption.


Potential Hazards

  • Ballistic projectiles: These are large pieces of rock that are ejected from the volcano at high velocity.
  • Pyroclastic flows: These are fast-moving mixtures of hot gas and rock that can travel at speeds of up to 700 kilometers per hour.
  • Lahars: These are mudflows that can contain large amounts of debris, including boulders and trees.
  • Ashfall: This can coat the ground and make it difficult to breathe.
  • Toxic gases: These can include sulfur dioxide, carbon monoxide, and hydrogen sulfide.


Some examples of phreatomagmatic eruptions include:

  • The eruption of Mount Ontake in Japan in 2014.
  • The eruption of Mount Taupo in New Zealand in 185 AD.
  • The eruption of Mount St. Helens in the United States in 1980.

Phreatomagmatic eruptions can be very difficult to predict, as they can occur with little or no warning. However, there are some signs that may indicate that an eruption is imminent, such as increased seismic activity, changes in groundwater levels, and the release of gases from the volcano. If you live near a volcano, it is important to be aware of the risks and to have a plan in place in case of an eruption.