May 4, 2006
A weekly feature provided by scientists at the Hawaiian Volcano Observatory.
East Lae`apuki: The bench that keeps on giving
Last November, 13.8 hectares (34 acres) of newly formed land and 4 hectares (10 acres) of former coastline at East Lae`apuki plunged into the ocean without warning. After this record-breaking collapse, a new bench has formed that is even larger than the last.
The continuous flow of lava into the ocean has created one of the largest benches in the history of this 23-year-long eruption. This gigantic bench is currently about 1,015 m (1,110 yards) long and 317 m (347 yards) wide, covering an area of about 13.8 hectares (44 acres), or roughly 40 football fields.
So why do these benches collapse? The bench is building out over a steep submarine slope of lava flows, fragmented lava, and black sand that forms by the explosive interaction of lava and the sea. As you can imagine, such a slope is very unstable and prone to submarine landslides.
In recent months, the bench had developed major cracks, parallel to the coastline, that ran nearly its entire length. Several weeks ago, as we observed the bench from a helicopter, we were surprised to see that most of the cracks contain water.
Near the center of the bench, the cracks are about 1 m (1.1 yards) wide, and the level of the water is about 3 m (3.3 yards) below the bench surface. This means the lava tube that carries lava across the bench to the ocean must be at least 4 to 5 m (4.4-5.5 yards) below the surface.
Two weeks ago, breakouts at the tip of the bench resurfaced the front of the bench. Many of the cracks have subsequently been buried by the new lava flows, giving the bench a smooth, inviting look.
The bench may look sound, but don't let its appearance belie its dangers. The presence of cracks on the bench, though now buried, indicate that the bench remains very unstable. Walking on or near the bench is extremely hazardous and, thus, the area around the ocean entry has been closed by the National Park Service.
Despite the closures and warnings, people continue to enter the closed area in the evening, sometimes even venturing out onto the bench. There have already been four deaths associated with active benches. The ocean entry was first closed because of concern for a collapse, such as the one in November, and it remains closed because the growth-and-collapse cycle is likely to be repeated. These collapses can occur without warning, so anyone unfortunate enough to be on or near the bench when it collapses risks being hit with a barrage of rocks and spatter, scalding waves, or, worse yet, plunging into the ocean along with the land that once appeared to be stable.
This past week, activity levels at the summit of Kilauea Volcano have remained at background levels. The number of earthquakes located in the summit area is low (usually less than 10 per day). Extension of the summit caldera, indicating inflation, appears to have resumed after pausing earlier in April.
Eruptive activity at Pu`u `O`o continues. On clear nights, glow is visible from several vents within the crater. Lava continues to flow through the PKK lava tube from its source on the flank of Pu`u `O`o to the ocean, with frequent surface flows breaking out of the tube near the 2,300-ft elevation, and a persistent flow, known as the "March 1 breakout," active on the coastal plain.
Lava continues to enter the ocean at East Lae`apuki, in Hawai`i Volcanoes National Park. The active lava bench continues to grow following the major collapse of November 28 and is now approximately 1,000 m (3,300 ft) long by 315 m (1,000 ft) wide, with a total area of 17 ha (42 acres).
On April 24, the March 1 breakout reached the ocean about 175 m (575 ft) east of East Lae`apuki. A small volume of lava continued to enter the ocean at this location through at least the morning of April 29 but has been inactive since.
Access to the ocean entries and the surrounding area remains closed, due to significant hazards. If you visit the eruption site, check with the rangers for current updates, and remember to carry lots of water when venturing out onto the flow field.
There was one earthquake beneath Hawai`i Island reported felt within the past week. A magnitude-2.2 earthquake occurred at 8:58 p.m. H.s.t. on Sunday, April 30, and was located 5 km (3 miles) northeast of Kapoho at a depth of 2 km (1 mile).
Mauna Loa is not erupting. During the past week, earthquake activity remained low beneath the volcano's summit (nine earthquakes were located, six of which were deep and long period in nature). Extension of lengths between locations spanning the summit, indicating inflation, continues at slow rates.
Updated: May 8, 2006 (pnf)