What causes a phreatic eruption?

A phreatic eruption happens when extreme heat from magma vaporizes ground water or surface water almost instantly. This sudden steam-blast sends out explosions of water, ash, rock, and gas, usually without including liquid lava. These steam explosions can precede larger volcanic events or create broad, low-relief craters known as maars.

What we know

• Phreatic eruptions occur when magma heats ground water or surface water, causing near-instantaneous evaporation. [2]
• The extreme temperature of magma causing these explosions ranges from 500 to 1,170 degrees Celsius, and volcanologists also categorize related steam-blast events under terms like ultravulcanian eruptions. [1, 2]
• Volcanologists classify an event as phreatomagmatic if molten magma is included in the ejected fragments. [2]
• Phreatic explosions can release toxic emissions such as carbon dioxide and hydrogen sulfide gases. [2]

Where to go next

• compared withWhat happens during a phreatomagmatic eruption?
• what followedHow do maars form from steam explosions?
• what caused itWhat triggers a Plinian volcanic eruption?
• whereHow is Mount Mayon's volcanic activity monitored?
• a case in pointWhat was the Oruanui supereruption?
• an unexpected connectionHow can a steam explosion release deadly poisons?While steam and rock are the expected output of water hitting magma, these explosions can also emit lethal concentrations of carbon dioxide and hydrogen sulfide.

Sources

• [1]phreatic eruption (Wikidata Q1067217) · CC0 1.0
• [2]Phreatic eruption · CC BY-SA 4.0
• [3]Mayon · CC BY-SA 4.0
• [4]Oruanui eruption · CC BY-SA 4.0
• [5]Plinian eruption · CC BY-SA 4.0