Report on Kilauea (United States) — December 1990
Bulletin of the Global Volcanism Network, vol. 15, no. 12 (December 1990)
Managing Editor: Lindsay McClelland.
Kilauea (United States) East rift lava continues to enter sea; briefly increased lava lake activity after seismic swarm
Please cite this report as:
Global Volcanism Program, 1990. Report on Kilauea (United States) (McClelland, L., ed.). Bulletin of the Global Volcanism Network, 15:12. Smithsonian Institution.
19.421°N, 155.287°W; summit elev. 1222 m
All times are local (unless otherwise noted)
Through December 1990, lava from Kupaianaha continued to advance through tube systems on the E and W sides of its 1986-90 flow field. Flows entered the ocean throughout December in a zone ~500 m wide on the W side of the lava field (figure 75). The low-level volcanic tremor registered near Kupaianaha and Pu`u `O`o vents continued without marked variations, and tremor was vigorous near the W ocean entry. Summit seismicity increased in late December and early January and the E-W component of summit tilt showed >20 µrad of inflation since September (figure 76).
|Figure 75. Lava produced by Kilauea's east rift eruption, 1983-90. Arrows indicate lava flow in tubes, and crosses at the coast mark areas where lava was entering the ocean. Courtesy of HVO.|
|Figure 76. N-S and E-W components of tilt measured by the water-tube tiltmeter at the summit of Kilauea, and daily number of shallow summit earthquakes, 1 January 1989-7 January 1991. Courtesy of HVO.|
Summit seismicity and tilt, associated with increased activity at Pu`u `O`o, suggest that an intrusion occurred in early December. A shallow microearthquake swarm in the summit region began at about 1600 on 4 December and continued until the following midmorning. After the initial swarm events, volcanic tremor increased and was at sustained high levels between 1735 and 1810. Summit tilt data indicated a trend of rapid inflation coincident with increasing amplitude of summit earthquakes and tremor. Shallow seismicity continued, extending over a larger area from the summit roughly 8 km SE to the vicinity of Mauna Ulu. The swarm activated what is believed to be a magma conduit connecting the summit and East rift zone. In the past, this feature had consistently sustained small earthquakes, but the seismicity had been much less intense. Although no changes were apparent in the continuing tremor farther down the East rift zone at Pu`u `O`o and Kupaianaha, lava lake activity increased briefly at Pu`u `O`o. At 1700 on 4 December, lava covered ~¼ of the rubble-filled crater floor. When observed the next day, the entire floor was lava-covered, but by the 6th the lava lake had shrunk to its previous dimensions.
Most of the December lava from Kupaianaha moved through the W tube system to the sea, but small surface breakouts occurred in Royal Gardens subdivision and near the coast. No additional houses were destroyed. On the E side of the lava field, small flows covered another 50 m of Hwy 130 at the beginning of December. A small lava flow entered the sea (near the former Painted Church site) on 15 December and remained intermittently active for a few days, but was stagnant by the 20th. Another lobe of the same breakout moved slowly eastward along the forest line. By 17 December this lobe was 400 m from the nearest house in Kaimu, but stopped before reaching it. In late December, a larger breakout from the E tube system advanced to the Hakuma fault scarp and began to cover new land near the area's two remaining homes. This flow remained active at the end of December, when it was moving both E and W along the scarp on a front > 500 m wide. One of the houses was overrun by lava on 10 January.
On the morning of 25 December, many small summit events began to be recorded. Earthquake counts totaled hundreds daily, with nearly 1,000 on several days (figure 76). During the first week in January, summit microearthquake activity continued, at rates that exceeded 1,000 events/day. Many appeared to have a more harmonic character (dominant frequency ~10 Hz) than typical summit short-period earthquakes. On 2 January, a series of intermediate-depth long-period events occurred at the summit, with most intense activity between 0800 and 1000. A period of similar intense seismicity began on the morning of 7 January, tapering off the next morning.
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: T. Moulds, P. Okubo, and C. Heliker, HVO.