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Volcanic Hazards

When Lava Enters the Sea

Tephra-jet explosion at lava entry point, Kilauea Volcano, Hawai`i Tephra-jet explosion at lava entry point, Kilauea Volcano, Hawai`i

"Two mighty agencies in collision. Two antagonist and gigantic forces in contact, and producing effects on a scale inconceivably grand!"

"The atmosphere in all directions was filled with ashes, spray, gases... while the burning lava, as it fell into the water, was shivered into millions of minute particles, and, being thrown back into the air, fell in showers of sand on all the surrounding country. The coast was extended into the sea... and a pretty sand-beach and a new cape was formed."

T. Coan, minister in Hawai`i, 1841

Explosions and collapsing land endanger people

Such vivid descriptions and scenes of lava entering the sea along Kilauea's shoreline draw millions of people to Hawai`i who are hoping to witness for themselves growth of new land and experience the remarkable interaction of lava and water. Beautiful and stunning, the explosive interaction can be dangerous to visitors who venture too close to a lava entry point. Also, the new land created by lava entering the sea is unstable. Large areas regularly collapse into the sea, usually triggering a series of stronger explosions and sending a wave of scalding seawater onshore. Such explosions have hurled hot rocks and lava fragments more than 100 m (330 ft) inland!

Unfortunately, the entry of lava into the ocean is difficult to observe from a distance because it's often obscured by an energetic and acidic steam plume or by an abrupt cliff above the entry point. This often invites visitors to jeopardize their safety by walking right up to and over the point where lava enters the ocean. Activity that may appear stable and non threatening can actually change without warning, leaving no time for escape.

Steam plume above lava entry point
Photograph by T.N Mattox on September 23, 1993.

Lava entering the ocean is often hidden beneath a steam plume, which may draw unwary visitors too close to the entry point for safety.

Why are lava entries so dangerous?

New land created by lava entering the sea looks like a stable platform that extends a few tens to hundreds of meters into the ocean. We refer to this new land as a lava delta. But what can't be seen is the loose pile of unconsolidated lava fragments underneath that supports the new land. This pile of material can easily slide away when the growing delta advances over a steep submarine slope. Areas the size of several football fields can collapse into the ocean with little or no warning.

People standing on a growing lava delta during a collapse event can be swept into the sea, splashed with scalding water, and hit by flying rock debris. Visitors to an active lava delta at Kilauea Volcano are advised not to venture onto the new land. Entry points can only be viewed safely from behind the former sea cliff and shoreline.

Hazardous activity near active lava deltas


Mattox, T.N, and Mangan, M.T., 1997, Littoral hydrovolcanic explosions: a case study of lava-seawater interaction at Kilauea Volcano: Journal of Volcanology and Geothermal Research, v. 75, p. 1-17. skip past bottom navigational bar

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How Hawaiian Volcanoes Work

The URL of this page is http://hvo.wr.usgs.gov/hazards/oceanentry/
Contact: hvowebmaster@usgs.gov
Updated: 18 June 2001 (pnf)