Overview

The eruption of Pu`u `O`o continues to generate a variety of activity on the pali and coastal plain as lava travels from the vent through a lava-tube system to the ocean. Periodically, the supply of magma to the vent is cut off for short periods of time. The 23rd such interruption in the current eruptive episode 55 lasted for only about 33 hours beginning on May 4, but it was long enough for the steam plume at the entry area to stop and for a sluggish 6-week-old pahoehoe flow on the coastal plain to stagnate. When lava began flowing again through the tube system late on May 5, several small surface flows poured anew onto the pali and coastal plain. Lava finally reached the ocean through the preexisting tube system on May 7.

No significant changes have occurred recently at Pu`u `O`o. At the coastal entry area, however, the lava bench changes constantly as new land is created and then collapses into the ocean. Frequent explosions of varying intensity also hurl lava fragments onto the bench and atop the sea cliff.

23rd Pause of Episode 55

This most recent pause in the eruption was very brief, beginning at about 1 p.m. on May 4 and ending at about 10 p.m. on May 5. The eruption resumed slowly, and as lava moved through the tube system, only a few sluggish flows broke out onto the pali and coastal plain.

View from ocean to Pu`u `O`o	Lava delta without steam plume
[Medium-sized image] [Large-sized image]	[Medium-sized image] [Large-sized image]

Pahoehoe flow inflates with new lava	Pahoehoe flow spreads laterally
[Medium-sized image] [Large-sized image]	[Medium-sized image] [Large-sized image]

View into North Pit of Pu`u `O`o

Lava visible in spatter cone within Pu`u `O`o
Photograph by J. Kauahikaua on April 30, 1999

Observations into the deep crater of Pu`u O`o` are not possible most of the time because of the thick plume of steam and sulfur dioxide gas rising into the atmosphere. The vent continues to release an average of about 2,000 tons of sulfur dioxide gas each day. Lava is sometimes visible in the northernmost pit on the crater floor (photograph above). When viewed on May 6, a small spatter cone was visible in this pit.

Explosions from lava bench on April 13

A series of strong explosions from the active lava bench on April 13 were likely related to the progressive collapse of the leading edge of the delta into the ocean. As the lava tubes were sheared off by the collapses, seawater gained access to the remaining tube system and a much larger than usual volume of lava was suddenly exposed to seawater. Both processes led to strong steam-driven explosions that hurled lava bombs and hot rocks into the air as high as 80 m and inland nearly 100 m from the bench's edge. These ballistics did not land behind the warning signs posted by the National Park Service, however, located about 90 m from the sea cliff above the bench.

Photograph by J. Wightman on April 13 Ballistics reach height of 40 m	Photograph by J. Wightman on April 13 Ballistics reach height of 70-80 m

USGS eyewitness account of the explosions. "When we arrived at the ocean entry at about 2 p.m., two plumes were rising from the edge of the active bench. The widest part of the bench was about 40-45 m in width (a few hours earlier, it was about 80 m wide). Starting just before 4 p.m. the western plume area began venting mainly steam from a hole (probably a skylight) just inland from the outer edge of the bench. The venting sounded like a jet engine. Then just after 4 p.m. explosions from this new vent hurled spatter into the air and formed bubble fountains as large as 10-15 m in diameter."

"This activity turned highly explosive within a few minutes, hurling spatter and rocks as high as 80 m (average height of spatter was between 50 and 60 m). Spatter and hot rocks from the explosions fell to the ground atop the sea cliff more than 75 m from the source. The explosive activity continued for about 90 minutes and then intermittently for the next few hours. One explosive episode caused lightning in the plume. When we arrived at our car parked 5 km away at the end of the Chain of Craters road, we found a thin layer of tiny brown flakes of glass from the exposions on the windshield."

Pahoehoe flow creeps across coastal plain, March 26-May 4

Photograph by J. Kauahikaua on March 31, 1999
Source of breakout from lava tube on coastal plain

Lava broke out from the tube system on March 26 about 2 km from the ocean. The breakout fed a wide, slow-moving pahoehoe flow for the next 5 weeks. The flow had advanced to within about 700 m of the ocean when the supply of lava in the tube system was shut off by the pause on May 4. In the photograph above, the surface of the new pahoehoe flow is about 2 m below the top of the rise at its source.

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.