Volcano Watch - Creation of new land is awesome, unstable, and full of surprises

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Lava flows spilling into the sea on the south coast of Kīlauea Volcano for the past several months have added nearly 30 acres of new land to Hawai`i island and drawn tens of thousands of people to witness it. Most of Kīlauea's visitors don't realize, however, that much of the "new land" they see ends up sliding into the ocean.

Aerial view of East Lae`apuki lava delta

Aerial view looking west of East Lae`apuki lava delta. Smooth surface is most recent lava flows. Note fan of flows reaching onto delta from upper right, the site of the feeding tube. (Public domain.)

Therein lies the fascination for volcano watchers and the very real danger of getting too close to creation. Depending on how the land collapses into the sea, the beautiful and dazzling interplay between molten rock and water can literally be earth-shaking, explosive, or deadly.

Lava is currently entering the sea at two locations near Lae`apuki and Kamoamoa, former Hawaiʻian village sites already extensively covered by lava flows from the current eruption. The actively growing new land at these sites may appear to be stable platforms or lava benches extending into the sea. They are anything but stable.

The more active Lae`apuki bench is about 10 hectares (25 acres) in size and measures 1,420 m long (4,660 ft) and 220 m (722 ft) wide at its widest part. The Kamoamoa bench is about 1.6 hectares (4 acres) and measures 700 m (2,300 ft) long and 70 m (230 ft) wide.

These active benches are being built on top of an extensive pile of loose lava fragments that form as molten lava enters the ocean and shatters. The fragments accumulate on the steep submarine slope just offshore and are then covered with a veneer of lava flows, forming the bench.

The pile can easily slide away when the growing bench advances over the steep submarine slope of Kīlauea. Areas the size of a kitchen table frequently slide in the sea as the bench grows, but the more spectacular and dangerous collapses involve areas the size of several football fields that disappear with little or no warning.

The largest bench collapse during the current eruption occurred at Lae`apuki on December 2, 1996. At the time, the bench was 750 m (2,460 ft) long and more than 200 m (650 ft) wide. During a 2.5-hour period, the entire bench and part of the sea cliff slid away in a series of 20 slides. Explosions hurled hot rocks as far as 100 m (330 ft) inland from the sea cliff.

An extensive series of cracks has developed in the active Lae`apuki bench parallel to the most recent sea cliff. The cracks are discontinuous but cut across nearly the entire length of the bench. The wide-ranging distribution of the cracks clearly indicates that the entire bench is settling and unstable, but the cracks do not necessarily mean that the entire bench will collapse.

Like the event in 1996, a collapse of the Lae`apuki bench would expose a large volume of lava and extremely hot, newly solidified lava flows to seawater and trigger steam explosions. Volcano watchers standing on the sea cliff would likely not have sufficient time to outrun the rain of lava fragments and hot rocks.

Also, the displacement of seawater by a collapsing bench can send hot waves onto shore. People have received second-degree burns and died from scalding water and steam rushing over an active bench.

They are, however, not the only hazards present along Kīlauea's south coast. Lava feeding both benches passes through lava tubes originating on the southern flank of the Pu`u `O`o vent. Great care must always be taken when hiking near or over an active lava tube, especially near skylights. The roof of a lava tube frequently collapses, creating a new skylight, or erodes and becomes so thin that it might not support the weight of an unsuspecting hiker.

The roof of the lava tube system inland from the Lae`apuki bench is now extremely thin (measured in a few centimeters (inches) in several places over a distance of a few hundred meters (yards)). Thin tube roofs are not known to "heal" themselves, so this area should be avoided until a completely new tube system develops. Heed the National Park warning signs an do not venture into this area.

Volcano Activity Update

Eruptive activity at Pu`u `O`o continues. On clear nights, glow is visible from several vents within the crater and on the southwest side of the cone.

The PKK lava tube continues to produce intermittent surface flows from above the top of Pulama pali to the ocean, but the amount of visible surface lava is minimal. Two ocean entries, at East Lae`apuki and East Kamoamoa, were active as of July 7. Access to the ocean entries and the surrounding area, however, has been closed due to significant hazards. Unfortunately, the breakout on the coastal plain near the base of Paliuli, active for the last few weeks, has apparently stagnated. This means that there are no easily accessible surface flows at the eruption site. If you do visit the eruption, check with the rangers for updates to this situation, and remember to carry lots of water when venturing out onto the flow field.

During the week ending July 6, no earthquakes were felt on Hawai`i Island.

Mauna Loa is not erupting. During the week ending July 6, only three earthquakes were recorded beneath the summit area. None of them were deep or long-period in nature. Inflation continues at a slightly increased rate over the last few weeks.