Report on Kilauea (United States) — May 1999
Bulletin of the Global Volcanism Network, vol. 24, no. 5 (May 1999)
Managing Editor: Richard Wunderman.
Kilauea (United States) Bench collapse on 13 April; a 33-hour eruptive pause on 5 May
Please cite this report as:
Global Volcanism Program, 1999. Report on Kilauea (United States) (Wunderman, R., ed.). Bulletin of the Global Volcanism Network, 24:5. Smithsonian Institution. https://doi.org/10.5479/si.GVP.BGVN199905-332010.
19.421°N, 155.287°W; summit elev. 1222 m
All times are local (unless otherwise noted)
The eruption of Pu`u `O`o continued to generate a variety of effects on the pali (cliff or fault scarp) and coastal plain during April and May as lava traveled from the vent through a lava-tube system to the ocean. At the coastal lava-entry area the lava bench repeatedly changed as new deposits built up and collapsed. Frequent explosions threw lava fragments into the ocean, onto the bench, and to the top of the adjacent sea cliff.
In the past, the supply of magma to the vent has been cut off for short periods; the 23rd such pause in the eruption began at about 1300 on 4 May and ended around 2200 on 5 May, only about 33 hours. That was long enough for both the steam plume at the ocean-entry area to stop (figure 136) and for a sluggish 6-week-old pahoehoe flow on the coastal plain to cease advancing. The eruption resumed slowly, and as lava moved through the tube system, only a few small sluggish flows broke out onto the pali and coastal plain (figure 137). Lava finally reached the ocean through the preexisting tube system on 7 May.
|Figure 137. A short-lived pahoehoe flow at Kilauea that began after pause #23 (4-5 May 1999) had ended. Courtesy of HVO; photograph by S.R. Brantley.|
Lava broke out from the tube system on 26 March about 2 km from the ocean. The breakout fed a wide, slow-moving pahoehoe flow for the next five weeks. The flow had advanced to within ~700 m of the ocean when the supply of lava was shut off by the pause on 4 May.
No significant changes have occurred recently at the Pu`u `O`o cone. Observations into the deep crater of Pu`u `O`o are usually not possible because of the thick plume of steam and SO2 gas. The vent continued to release an average of 2,000 tons of SO2 gas each day during April and May. Lava was sometimes visible in the northernmost pit on the crater floor; and when viewed on 6 May, a small spatter cone was visible in this pit.
Explosions at lava bench on 13 April. A series of strong explosions from the active lava bench on 13 April was likely related to the progressive collapse of the leading edge of the delta. As the lava tubes were sheared off by the collapses, seawater entered the 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 (figure 141). These ballistics did not land behind the warning signs posted by the National Park Service about 90 m from the sea cliff above the bench.
|Figure 141. Lava bombs flying inland from the site of steam explosions at the ocean entry point on 13 April. Courtesy of HVO; photograph by J. Wightman.|
USGS observers said that when they arrived at the ocean entry area at 1400 on 13 April two plumes rose from the edge of the active bench. The widest part of the bench was ~40-45 m, where a few hours earlier the bench was as wide as 80 m. Starting just before 1600 the W plume area began venting steam from a hole (probably a skylight) just inland from the outer edge of the bench; the venting sounded like a jet engine. A few moments later 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 into the air (average height of spatter was between 50 and 60 m). Ejected materials fell to the ground atop the sea cliff more than 75 m from the source. Explosive activity continued steadily for about 90 minutes and returned intermittently during the next few hours. One explosive episode caused lightning in the plume. When the witnesses returned to their car, parked 5 km away at the end of the Chain of Craters road, they found a thin layer of tiny brown flakes of glass from the explosions on the windshield.
Background. Kilauea is one of five coalescing volcanoes that comprise the island of Hawaii. Historically its eruptions originate primarily from the summit caldera or along one of the lengthy E and SW rift zones that extend from the caldera to the sea. The latest Kilauea eruption began in January 1983 along the east rift zone. The eruption's early phases, or episodes, occurred along a portion of the rift zone that extends from Napau Crater on the uprift (toward the summit) end to ~8 km E on the downrift end (toward the sea). Activity eventually centered on the area and crater that were later named Pu`u `O`o. Between July 1986 and January 1992, the Kupaianaha lava lake was active ~3 km NE (downrift) of Pu`u `O`o. It was during this period that the town of Kalapana and most of the 181 homes lost were destroyed. In December 1991, one month before the shutdown of Kupaianaha, eruptive activity returned to Pu`u `O`o. More than 1 km3 of lava was erupted from January 1983 through January 1997.
Geologic Background. Kilauea, which overlaps the E flank of the massive Mauna Loa shield volcano, has been Hawaii's most active volcano during historical time. Eruptions are prominent in Polynesian legends; written documentation extending back to only 1820 records frequent summit and flank lava flow eruptions that were interspersed with periods of long-term lava lake activity that lasted until 1924 at Halemaumau crater, within the summit caldera. The 3 x 5 km caldera was formed in several stages about 1500 years ago and during the 18th century; eruptions have also originated from the lengthy East and SW rift zones, which extend to the sea on both sides of the volcano. About 90% of the surface of the basaltic shield volcano is formed of lava flows less than about 1100 years old; 70% of the volcano's surface is younger than 600 years. A long-term eruption from the East rift zone that began in 1983 has produced lava flows covering more than 100 km2, destroying nearly 200 houses and adding new coastline to the island.
Information Contacts: Hawaiian Volcano Observatory (HVO), U.S. Geological Survey, PO Box 51, Hawaii Volcanoes National Park, HI 96718, USA (URL: https://volcanoes.usgs.gov/observatories/hvo/).