Phreatomagmatic (Hydrovolcanic) Eruptions

Explosive eruption column
Explosive eruption column above Halema‘uma‘u Crater, Hawai’i on May 18, 1924.

Photo by K. Maehara, Public domain.


Violently-explosive eruptions driven by steam explosions produced by the interaction of hot magma with surface water or shallow groundwater. Hydrovolcanic eruptions include tephra derived from juvenile magma.

These eruptions produce tephra and steam.

Tuff Rings and Maars

Hydrovolcanic eruptions build tuff rings and maars such as Ubehebe Craters, a group of maars in Death Valley National Park, and the Espenberg maars in Bering Land Bridge National Preserve.

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low-relief, broad crater lake
Devil Mountain Maar Lakes, Bering Land Bridge National Preserve, 2015.

NPS photo.

Crater Explosions

They have also occurred in the summit of Kilauea in Hawai’i Volcanoes National Park, most recently in the May 1924 explosive eruption when the lava level in Halema’uma’u (the summit crater) dropped allowing interaction between magma and groundwater.

diagram of how explosive eruptions occurring when 1) magma column drops below water table, 2) groundwater interacts with hot rock, and 3) steam pressure builds then explodes
At Kīlauea, when the lava column drops below the water table, groundwater may come into contact with with magma or hot rocks, causing violent steam explosions.

Swanson et al. 2011, public domain, USGS.

Related Links

Part of a series of articles titled Volcanic Eruption Types.

Bering Land Bridge National Preserve, Death Valley National Park, Hawaiʻi Volcanoes National Park

Last updated: April 14, 2023