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Lava entering ocean

Lava entering the ocean creates a distinctive set of hazards that have seriously injured or killed unsuspecting people eager to see up close the interaction of hot lava and cool seawater.

Ocean entry hazards


Lava enters ocean at Kupapa‘u Point, Kīlauea Volcano, Hawai‘i. Phot...
Lava enters ocean at Kupapa‘u Point, Kīlauea Volcano, Hawai‘i. Photographed with a telephoto lens, the safest way to view the interaction of lava and seawater on the edge of an active delta. (Public domain.)

Getting too close to an ocean entry, either on land or from the sea, is potentially deadly. Primary hazards include:

  1. Sudden collapse of a lava delta (new land created at ocean entry) and the adjacent sea cliff into the ocean.
  2. Large explosions triggered by delta collapse.
  3. Waves of scalding hot water from ocean swells and delta collapse.
  4. Steam plumes that rain hydrochloric acid and tiny volcanic glass particles downwind from the entry point.

Visitors to an active ocean entry should pay attention to warning signs that may be posted in the area.

Scientists cannot predict the timing or size of a lava delta collapse. They also cannot predict which direction and how far fragments of lava and rock will be hurled on land or seaward during a collapse-triggered explosion. The best way to avoid these hazards is to never walk onto an active lava delta and maintain a safe distance from a delta's leading edge, even when on a boat. Once a new lava delta extends more than a few tens of meters (yards) from the old sea cliff, visitors should stay at least 300 m (330 yd) away from where lavais entering the ocean. This is the maximum distance rocks and spatter have been thrown inland from the older sea cliff during past ocean-entry explosions. Small rock fragments can fall far beyond this distance.


Early lava delta growth along steep submarine slope. Loose lava fra...
Molten lava pouring into the ocean cools and shatters into sand- to block-sized fragments. These pieces accumulate along the steep submarine slope. (Credit: Johnson, Jenda. Public domain.)

Lava deltas collapse without warning


Lava entering the ocean builds a delta on top of unstable lava fragments along the steep submarine slope. As the delta grows seaward and laterally along the shoreline, it may slowly settle or sink as the loose rock debris shifts under the weight of overlying lava flows. This subsidence may allow seawater to get into the lava tube system, which can generate lava bubble bursts and rare littoral lava fountains (see gallery).

Growing lava delta. As lava flows and loose lava fragments build fo...
A lava delta may extend tens to hundreds of meters beyond the old shoreline. (Credit: Johnson, Jenda. Public domain.)

All or part of the delta can collapse into the ocean when the underlying debris can no longer support the delta's growing mass or is undercut by a deeper submarine landslide. The collapses occur suddenly or over a period of several hours. Despite a well-posted warning signs in Hawai‘i Volcanoes National Park, a large delta collapse in 1993 caught many people by surprise—a photographer standing on the delta was swept out to sea and lost. More than a dozen other people were injured when they raced to stable ground amidst a shower of hot rocks.

Active lava delta collapse can trigger explosions that hurl blobs o...
The leading edge of a growing lava delta collapses when the loose debris underneath slides down the submarine slope. The failure occurs because the loose fragmented debris underneath can no longer support the delta's growing mass or a deeper submarine landslide undercuts the delta. (Credit: Johnson, Jenda. Public domain.)


Explosions often triggered by delta collapse


Lava entering the ocean generates different types of explosive interactions with seawater. The largest and most dangerous type of explosion is triggered by a delta collapse. The sudden mixing of seawater, hot rocks, and lava with temperatures about 1,150 degrees Celsius (2,100 degrees Fahrenheit) may cause steam-driven explosions from the collapsed area. Such explosions have hurled hot rocks nearly a meter (yard) in size as far as about 250 m (273 yards) inland from the collapsed delta and scattered rock debris onshore over an area the size of several football fields. These explosions also hurl rocks seaward, probably to similar distances.


Waves generated by delta collapse heated to scalding temperatures


Large portions of an active lava delta are extremely hot because of lava flows on its surface, lava tubes beneath the surface, and still-hot solidified flows throughout a delta. A larger than usual ocean wave that sweeps across the surface of a hot delta can quickly reach scalding temperatures. People standing near lava deltas have received second-degree burns from such hot waves and accompanying steam. In 2000, the deaths of two severely burned individuals found near an active coastal lava flow were caused by the inhalation of acidic steam from an ocean entry, according to the medical examiner. Delta collapses can also produce waves both onshore and offshore, which can imperil boats next to a collapsing delta.


Ocean-entry plume is acidic


A white plume on the edge of an active lava delta marks where lava meets seawater—this plume can cause skin and eye irritation and breathing difficulties and should be avoided. As hot lava boils cool seawater, a series of chemical and physical reactions create a mixture of condensed, acidic steam, hydrochloric acid gas, and tiny shards of volcanic glass. Blown by wind, this plume creates a noticeable downwind haze, known as "laze" (short for lava haze).

During prevailing trade-wind conditions, which exist more than about 80 percent of the time, air flow from mid-morning through late afternoon carries the plumeonshore and along the coast. This can cause poor air quality for people downwind of the ocean entry. From nighttime through early morning, trade-wind flow typically blows the laze off shore and out to sea.

Kīlauea Volcano's east Lae‘apuki lava delta pictured hours before i...
Kīlauea Volcano's east Lae‘apuki lava delta pictured hours before it collapsed into the sea over a 90-minute period. White plume marks location of lava entering sea fed by a lava tube within delta. (Public domain.)
Kīlauea Volcano's east Lae‘apuki lava delta after 70-100 m (230-330...
Kīlauea Volcano's east Lae‘apuki lava delta after 70-100 m (230-330 ft) long section collapsed into ocean producing scalding waves, a steam white out and hurled rocky debris onto surface (foreground). (Public domain.)





Active lava delta on south coast of Kīlauea Volcano, Hawai‘i...
The eastern (right) lava delta is the larger of the two, with a broad span of small lava flows entering the sea creating a wide ocean entry plume. Fewer flows on the smaller western (left) entry created a weaker plume. (Public domain.)

Additional resources relating to ocean entry hazards


Fact Sheet
Viewing Hawai'i's Lava Safely—Common Sense is Not Enough

Volcano Watch Articles


Lava entering ocean image gallery: