VOLCANO WATCH: Beware of Lava Entering the Ocean

Less than 24 hours after first reaching the sea in the early morning hours of July 26, lava spilling over the sea cliff and into the ocean had started building a foundation of loose lava fragments on which a new lava delta can form. Lava deltas are extremely dangerous because they can collapse into the ocean without warning, triggering explosions that hurl rocks on and off shore, and sending waves of scalding water onto the coast. The area of active lava pouring over this sea cliff is about 66 feet wide and the cliff is about 66 feet high. USGS photo.

Lava erupting from the Puʻu ʻŌʻō vent entered the ocean along Kīlauea Volcano’s south coast this past week for the first time since 2013—perhaps the beginning of a new sustained lava entry that will add new land to the Island of Hawaiʻi.

This ocean entry is likely to draw thousands of people eager to experience the riveting interaction between hot lava and cool seawater.

When lava enters the ocean for sustained periods of time, the island-building activity creates a unique set of hazards that may be unknown to many people.

Four main hazards associated with lava flowing into the ocean include the sudden collapse of new land and adjacent sea cliffs into the ocean, explosions triggered by the collapse, waves of scalding hot water washing onshore, and a steam plume that rains hydrochloric acid and tiny volcanic glass particles downwind from the entry point.

The first three of these hazards can be deadly or cause serious injury. The fourth—steam plumes—can cause breathing difficulties, particularly for people with pre-existing respiratory diseases. This is because inhaling or contacting the acid gases and liquids in the plume can irritate skin, eyes and respiratory tracts.

Lava streaming into the ocean cools rapidly and shatters into sand-sized and larger angular pieces of glassy rock. As these fragments accumulate on the steep submarine slope, they build an unstable foundation upon which lava flows can spread above sea level. This new land is called a lava delta.

As lava deltas grow seaward and along the shoreline, they slowly settle or sink as the loose debris shifts under the weight of the overlying lava flows. When the underlying debris can no longer support a delta’s growing mass, or is undercut by a deeper submarine landslide, the delta collapses into the ocean.

During a collapse, hot rocks, molten lava within tubes and/or surface lava flows instantly come into contact with seawater. With temperatures higher than 1,100 degrees Celsius (2,012 degrees Fahrenheit), active lava causes seawater to flash to steam, which triggers an explosive blast of rocks, steam and molten lava fragments into the air.

The largest of these explosions have hurled rocks nearly a yard in size as far as about 330 yards inland from the collapsed delta and have scattered rock debris over areas the size of several football fields.

During a large delta collapse in 1993, and despite a well-posted closure in Hawaiʻi Volcanoes National Park, a photographer was swept out to sea. More than a dozen other people were also injured when they attempted to flee the hot rocks and lava fragments hurled onshore.

Unexpected large waves produced by normal ocean swells or sudden collapse of an active lava delta can send scalding hot water crashing onto shore, both inland and adjacent to lava deltas. People standing in these areas have received second-degree burns from the hot water swept onshore. 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 the ocean entry, according to the medical examiner.

Scientists cannot predict the timing or size of a delta collapse, or the exact direction or distance that rocks will be hurled during a collapse-triggered explosion. The best way to avoid these hazards is to never walk onto an active lava delta and once a new lava delta extends a few tens of yards from the old sea cliff, stay at least one-quarter mile away from where lava enters the sea. Small rock fragments can even fall beyond this distance during large explosions triggered by lava delta collapse.

More information about the hazards associated with ocean entries is available on the USGS Hawaiian Volcano Observatory website. Tips for safe hiking and lava-viewing near ocean entries are provided in a USGS Fact Sheet posted online, as well as from National Park Service rangers.

Volcano Activity Updates
Kīlauea continues to erupt at its summit and East Rift Zone. During the past week, the summit lava lake level varied between about 21.5 m and 26 m (70 and 85 feet) below the vent rim within Halema‘uma‘u Crater.

On the East Rift Zone, the “61g” flow continued to advance to the southeast, and, at 1:15 a.m., HST, on July 26, 2016, lava reached the ocean for the first time since August 2013. The lava flow does not pose an immediate threat to nearby communities.

Mauna Loa is not erupting. In the past week, earthquakes at Mauna Loa occurred beneath the west flank of the volcano mostly in the 5 to 11 km (3 to 7 miles) depth range. In addition, earthquakes are occurring in south caldera and upper Southwest Rift Zone at depths less than 5 km (3 miles).

Seismicity rates on Mauna Loa overall were lower this week compared with the previous update. Global Positioning System (GPS) measurements show deformation related to inflation of a magma reservoir beneath the summit and upper Southwest Rift Zone, with inflation occurring mainly in the southwestern part of the magma storage complex.

Two earthquakes were reported felt on the Island of Hawaiʻi this past week. On Friday, July 22, at 9:16 p.m., HST, a magnitude-4.3 earthquake occurred 5.4 km (3.3 miles) northwest of Captain Cook at a depth of 11.5 km (7.1 miles). On Tuesday, July 26, at 2:33 p.m., HST, a magnitude-2.7 earthquake occurred 2.1 km (1.3 miles) southeast of Kīlauea Summit at a depth of 0.9 km (.6 miles).

Volcano Watch is a weekly article and activity update written by U.S. Geological Survey Hawaiian Volcano Observatory scientists and affiliates.