When seawater and lava mix within the confines of a lava tube, a steam explosion often results, sometimes blasting lava up through a hole in the roof of the tube. In the photos above and below, such a steam-driven explosion sends a dome-shaped sheet of lava, the skin of a bursting bubble, called a bubble burst about 5 m into the air. Similar but larger steam-driven explosions occurred intermittently for several days after a major collapse of the active lava delta on March 8. As lava began rebuilding new land into the sea, water was apparently able to gain access to the developing lava-tube system within the delta.

Beginning lava bubble	Bubble begins to explode
[Medium-sized image] [Large-sized image]	[Medium-sized image] [Large-sized image]

Overview

The eruption of Pu`u `O`o continues to deliver lava to the sea through the lava-tube system that developed on the coastal plain in August 1998. No change has been observed at the Pu`u `O`o vent. On March 8, nearly all of the new land that was built since Decmeber 11, 1998, slid into the ocean. Based on an eyewitness account, the collapse probably occurred between about 00:30 a.m. and 02:00 a.m. and was accompanied by many intermittent explosions that hurled lava landward of the delta. The collapse removed part of the older sea cliff on the east and west sides of the active lava delta. Since the collapse event, lava has been constructing a new lava delta into the sea.

Collapse of New Land on March 8

Photograph by J. Kauahikaua on March 4, 1999
Area seaward of the white line fell into the sea on March 8

At the time of the collapse event, the lava delta was about 700 m long and extended as far as 200 m seaward from the previous shoreline and sea cliff; an estimated 10 hectares (25 acres) fell into the sea. On the east side of the delta (near side in photograph above), the former sea cliff was completely buried with lava, which allowed easy though unauthorized access for visitors hoping for closer views of lava entering the sea. The landward side of the western part of the delta, however, was marked by a cliff 10-15 m tall; this cliff was formed by a delta collapse on December 11, 1998. Warning signs posted by the National Park Service were at least 50 m landward of this cliff.

According to an eyewitness, seven people were on the delta when it began to collapse on March 8. The first sign of a change in the activity was a strong explosion that "rocked" the eyewitness where he lay on the ground above the buried cliff. An initial energetic burst of lava from the edge of the delta threw spatter as high as 70-80 m into the air; these height estimates were scaled from the people on the delta adjacent to the explosion source. As large splatter clots fell in all directions around them, the seven ran away from the shoreline but became temporarily trapped by the sea cliff on the west side of the delta. THe eyewitness used his flashlight to guide the trapped, endangered people to safety across to the eastern part of the delta.

It is not known when the delta actually collapsed into the sea. The fearful eyewitness left the area shortly after the explosions began, and the delta was gone when observed the next morning. This most recent collapse event is a strong reminder that the ocean entry area is extremely hazardous, and visitors are advised not to venture onto the active lava delta. The seven on the new land this time were lucky to have escaped with their lives.

Pre-March 8 shoreline marked by black line
March 11	March 18
[Medium-sized image] [Large-sized image]	[Medium-sized image] [Large-sized image]

Rare View Into Pu`u `O`o crater

Photograph by J. Kauahikaua on February 25, 1999
View toward west into crater of Pu`u `O`o

Favorable wind conditions permitted a good view into the crater of Pu`u `O`o in late February. Lava was visible in the bottom of one of the pits (see line pointing to lava on photograph above) as were several ledges around the edges of the pits; these ledges are remnants of the crater floor that collapsed into the pits as lava beneath Pu`u `O`o lowered during the past year. The most recent overflow of lava from the crater occurred in January 1998; the decline in crater activity since then is thought to be the result of lava downcutting through the 20+ m of loose tephra that underlies the lava tube system beneath the south flank of Pu`u `O`o. As lava erodes the tephra, the lava level within the crater lowers because the vents inside and outside the crater are in equilibrium.

New Tiltmeter Improves Monitoring at Pu`u `O`o

Photograph by D. Pusic on February 5, 1999
Scientists install a tiltmeter in hole 5 m below surface

A new tiltmeter station was successfully installed in February near Pu`u `O`o in order to better monitor the middle east rift zone and the intermittent pauses in supply of magma to the vent. The new site design and improved electronics have so far yielded data that are at least 10 times better than those from older tiltmeter stations on the volcano. This is the first of several new tiltmeters that are planned for both Kilauea and Mauna Loa volcanoes.

Record above shows tilt from the new tiltmeter station located about 1 km southwest of Pu`u `O`o. The tiltmeter is still settling after its installation in early February, but the resolution of the data is far better than that of older tiltmeter sites. Because the new instrument is located about 5 m below the ground, the daily temperature effects on the rocks around the instrument are much less than for the older, shallower instruments, which are typically less than 1 m deep. For those unfamiliar with tilt units, one microradian is roughly the tilt created by inserting a dime beneath the end of a 1-km-long beam.

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.