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July 9, 1998

A weekly feature provided by scientists at the Hawaiian Volcano Observatory.


Waha`ula, the coastal lava entry that will not die

When lava enters the sea, it begins a struggle to build new land. We name these entries for nearby geographic features--Lae`apuki, Kamoamoa, Kamokuna, Waha`ula, to list a few. For a brief time they become places memorable to anyone who visits and watches the spectacle of incandescent lava, immense steam plumes, and spattering explosions. That's how entries begin, but how do they end? Waha`ula is one of the two coastal sites where lava has been entering the ocean for the past year. The other is the Kamokuna entry, which lies 800 m (0.5 mi) to the west. The Waha`ula site lies seaward of Royal Gardens, within a stone's throw of the site of the Waha`ula Heiau. Lava overran the heiau completely on August 11, 1997, and reached the ocean a few hours later. The surface flows soon crusted over, and a tube developed through the core of a favorably situated flow. A littoral cone, the result of steam-driven explosions, grew to mark the site where the tube entered the ocean. For the next nine months this entry point discharged lava relentlessly. During this time the lava built a bench approximately 3.4 hectares (8.3 acres) in size, creating new land along Hawai`i's southeast coast.

Waha`ula's success as an ocean entry stems from the stable tube system of Episode 55. A single tube can be traced 9 km south from the Pu`u `O`o vent to the foot of Pulama pali. As it developed, the tube forked on the coastal plain, near Royal Gardens; lava was distributed equally between the Kamokuna and Waha`ula entries 2 km south of the fork. This forked system worked well until January 1998, when it was overwhelmed by a surge of lava. Numerous flows issued from weak points along the tube for nearly a month, repaving much of the coastal plain inland of the entries.

The Waha`ula branch of the tube never recovered from this blow. Most lava was diverted to the western branch, feeding lava into the sea at Kamokuna and increasing the size of the steam plume that billows from the ocean's edge there. Waha`ula's share of lava was diminished by a corresponding amount. The telltale steam plume at Waha`ula entry was weakened to about one-quarter of its previous vigor.

A near-fatal blow was struck in May 1998, when another eruptive surge fed new surface flows, again at the expense of lava transported in the Waha`ula branch of the tube. The steam plume nearly vanished. The lower reach of the tube ceased to carry lava, but the entry would not die. Waha`ula staggered back to life when those very lava flows that robbed the tube then spread across the bench and cascaded into the ocean. The flows haven't solidified completely. Instead, their molten cores allow a small part of the lava supplied from upslope to reach the ocean. Waha`ula refuses to die.

Today the Waha`ula entry persists with a dribble of lava entering the sea and a trifling steam plume that is dissipated almost before it rises above the cliffs. We think the end is near for the ocean entry at this site. Kamokuna is quickly becoming the only show in town for coastal entry viewing.

Eruption and Earthquake Update

Eruptive activity was visible in Pu`u `O`o during the past week with lava covering the crater floor on several occasions. The pool of lava cast a red glow that was reflected off the fume clouds hovering above the cone. As noted above, lava flows through a network of tubes from the vent to the coast and enters the ocean in two areas - weakly at Waha`ula and prodigiously at Kamokuna. The public is again reminded that these two areas are extremely dangerous. The National Park Service has restricted access to them because of frequent explosions that accompany collapses of the growing lava bench. On Monday evening, July 6, at 6:30 p.m., a 9-acre section of the Kamokuna bench collapsed.

Two earthquakes were reported felt during the past week. Residents of Leilani Estates and lower Puna reported feeling an earthquake at 9:09 p.m. on July 2. The magnitude 3.0 earthquake was located 5 km (3 mi) east of Puulena Crater at a shallow depth. A magnitude 3.0 earthquake at 5:56 a.m. on July 3 was felt by residents in Pahala. The epicenter of the earthquake was 8 km (5 mi) west of Pahala at a depth of 8 km (5 mi).

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Updated: 31 July 1998