Overview

Little has changed in the eruption of Pu`u `O`o in the past several weeks. Lava continues to travel through the lava-tube system from Pu`u `O`o to the coast and build new land, called a lava bench, into the ocean. Frequent collapses of the bench into the sea prevent the bench from extending seaward more than about 200 m from the former shoreline. Slow-moving pahoehoe flows continue to occasionally break out from the tube system on the broad coastal plain, and the 24th pause in the current eruptive episode occurred June 14-17. No significant changes have occurred at the Pu`u `O`o vent in the past several months, but scientists have recently identified a few new collapse structures on the south flank of the cone.

July 1, 1999

Aerial view of the lava bench, coastal plain, Pulama pali, and Pu`u `O`o vent, Kilauea Volcano.   [Medium-sized image] [Large-sized image]

24th Pause of Episode 55

What happens when lava stops flowing from the Pu`u `O`o vent into the lava-tube system? Is the supply of magma from the summit reservoir to the east rift zone reduced or is it completely shut off? Or is there a blockage directly beneath Pu`u `O`o?

Data from our new tiltmeter near Pu`u `O`o and at the the summit caldera suggest that during pauses 23 and 24, some magma was still moving into the east rift zone near Pu`u `O`o (see map at right and graph of tilt below).

Tilt of ground at summit and near Pu`u `O`o, pause 24

The pause began when a tiltmeter at the summit showed an outward tilt of the ground, which is represented by the increase in tilt of the top curve. This outward tilt indicates that magma was moving into the summit reservoir and accumulating there during the pause. Just after the beginning of the pause, the tiltmeter near Pu`u `O`o recorded a slight increase in tilt of the ground away from the east rift zone. This tilt indicates that some magma was probably still moving into the rift zone at the same time that magma was accumulating in the summit reservoir. The reversal in tilt, both at the summit and near Pu`u `O`o, at the beginning of this pause indicates that magma was moving into the east rift zone. We infer that the pause was likely related to a blockage that developed beneath Pu`u `O`o or immediately uprift. This tilt reversal pattern was also seen during the eruptive pause in May 1999.

Pause ends as lava enters tube system from Pu`u `O`o

Lava pours through tube system after pause	Pahoehoe flows break out from tube system after pause
[Medium-sized image] [Large-sized image]	[Medium-sized image] [Large-sized image]

Lava bench continues to grow and collapse

Photograph by J. Kauahikaua on June 24, 1999

This view of the lava bench is toward the southwest. The bench is about 200 m wide from the cliff to its seaward edge. Recent surface flows have poured over the cliff and made it easy for visitors to walk onto the dangeous bench unknowingly. Visitors to the entry area are advised to remain behind the warning signs posted by Hawai`i Volcanoes National Park.

The leading edge of the bench collapsed during the night of July 2-3. Scientists estimate that up to 75 m of the bench slid into the ocean, removing about 1.7 ha (4.1 acres) of new land or 20 percent of the bench. Strong explosions occurred intermittently during the next few days, reaching a climax on July 4th. Here is a description from a scientist who witnessed these explosions:

"Major explosions and jetting started on the bench at 6:14 p.m. Bubble bursts were occurring from 3 locations and lava fountaining was occurring from a vent on the western part of the bench. Lava was thrown up to 150 m into the air by the fountaining. The fountain produced a nested pair of cones, approximately 30-45 m in diameter and 5-7 m tall. The bubble bursts took place about 20-40 m inland of where the waves could reach. The bubbles were about 40 m in diameter, but a few reached 60 m."

"Most impressive was watching the entire cone and surrounding bench undulate like a liquid during the most vigorous bubble-burst activity. Between explosive episodes, a series of surface flows broke out, covering most of the visible bench. One flow that poured into the ocean built a tube through the surf, which led to a series of underwater explosions about 25 m offshore."

"We were also able to see the fireworks above Hilo Bay, but Pele's show was by far much better!"

Pits and craters on south flank of Pu`u `O`o

Photograph by J. Kauahikaua on July 1, 1999
Fume rises from shallow collapse pits on south flank of Pu`u `O`o

Many small pits have formed on the lava shield on the west and south side of Pu`u `O`o during the past couple of years. In early June, a new collapse pit about 8 m in diameter and 5 m deep was observed; flowing lava was visible briefly at the bottom of the pit a few days later. Puka nui, a large collapse pit on the southwest flank of Pu`u `O`o, has not changed in the past two months.

Flow-field Map

Eruption-viewing opportunities change constantly, refer to the HVO home page for current information. Those readers planning a visit to Kilauea or Mauna Loa volcanoes can get much useful information from Hawai`i Volcanoes National Park.