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Report on Kilauea (United States) — May 1981


Kilauea

Scientific Event Alert Network Bulletin, vol. 6, no. 5 (May 1981)
Managing Editor: Lindsay McClelland.

Kilauea (United States) Intrusion into the southwest rift

Please cite this report as:

Global Volcanism Program, 1981. Report on Kilauea (United States) (McClelland, L., ed.). Scientific Event Alert Network Bulletin, 6:5. Smithsonian Institution. https://doi.org/10.5479/si.GVP.SEAN198105-332010



Kilauea

United States

19.421°N, 155.287°W; summit elev. 1222 m

All times are local (unless otherwise noted)


HVO has documented an intrusion into the SW rift in early 1981. This rift intrusion is the 13th since the major earthquake of November 1975, but the first since that date in the SW rift. On 20 January at about 0300 an intense earthquake swarm began just S of the caldera (figure 5). A few earthquakes migrated northward into the caldera during the next 60 hours, but most of the activity remained in the area where the swarm began, at depths of 2.5-3.5 km. Reoccupation of dry tilt stations 21 January revealed that significant inflation had taken place in the swarm area since the last tilt measurements 13 days earlier.

Figure (see Caption) Figure 5. Locations of shallow (< 7 km) SW rift earthquakes during four time periods from 20 January to 18 March 1980.

During the next few days, some epicenters advanced about 3 km down the SE side of the upper SW rift, while earthquakes continued in the initial swarm area. Migration of the seismicity was initially measured in hundreds of meters per day, more than an order of magnitude slower than the 500-1,500 m/hour during previous intrusions into the E rift zone. Additional dry tilt measurements 28 January confirmed that the center of inflation had also moved SW, but to a point distinctly NW of the seismically active zone. Until early February, earthquakes remained within 3 km of the initial swarm area. Seismicity had been concentrated in the same region during the last intrusion and eruption episode in the SW rift, in December 1974.

On 6 February, seismic activity suddenly shifted to an zone about 17 km downrift from the caldera center and the rate of deflation increased sharply in the N caldera area, which had shown only minor tilt changes earlier in the episode. Intense seismicity was confined to less than 1 km of the rift for the next two days. Earthquakes propagated downrift 8-17 February, forming a narrow, tubular zone that rose (at an angle of about 40°) from depths of 7 to 2 km over about 3 km horizontal distance. These earthquakes eventually reached depths of only 1.5 km. Two clusters of less intense activity occurred uprift between this zone and the area of late January-early February activity.

Seismicity subsided considerab1y 17 February as inflation resumed in the N caldera area. By the end of the month much of the 15 µrad of deflation recorded on borehole tiltmeters since early February had been regained. The most active seismic zone continued to grow slowly (less than 100 m/day) downrift, reaching a length of 5 km by mid-March, but the number of events per day declined from a peak of 1800 in mid-February to 110-350 by late March. SW rift seismicity decreased gradually through April, reaching near-normal levels by the end of the month.

Geological Summary. Kilauea overlaps the E flank of the massive Mauna Loa shield volcano in the island of Hawaii. Eruptions are prominent in Polynesian legends; written documentation since 1820 records frequent summit and flank lava flow eruptions interspersed with periods of long-term lava lake activity at Halemaumau crater in the summit caldera until 1924. The 3 x 5 km caldera was formed in several stages about 1,500 years ago and during the 18th century; eruptions have also originated from the lengthy East and Southwest rift zones, which extend to the ocean in both directions. About 90% of the surface of the basaltic shield volcano is formed of lava flows less than about 1,100 years old; 70% of the surface is younger than 600 years. The long-term eruption from the East rift zone between 1983 and 2018 produced lava flows covering more than 100 km2, destroyed hundreds of houses, and added new coastline.

Information Contacts: Hawaiian Volcano Observatory, USGS.