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Report on Kilauea (United States) — September 1982


Kilauea

Scientific Event Alert Network Bulletin, vol. 7, no. 9 (September 1982)
Managing Editor: Lindsay McClelland.

Kilauea (United States) Fissure eruption in summit caldera

Please cite this report as:

Global Volcanism Program, 1982. Report on Kilauea (United States) (McClelland, L., ed.). Scientific Event Alert Network Bulletin, 7:9. Smithsonian Institution. https://doi.org/10.5479/si.GVP.SEAN198209-332010



Kilauea

United States

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

All times are local (unless otherwise noted)


"An eruption in the S part of the caldera began at 1844:40 on 25 September, following nearly 2 hours of a premonitory seismic swarm and an abrupt increase in summit tilt. The eruption continued for 15 hours. Lava erupted from a kilometer-long set of left-stepping enechelon fissures in the the southernmost part of the caldera (figure 10). The E and central parts of the vent system were oriented in the usual ENE direction, nearly parallel to the nearby caldera wall. In the W part, however, the fissure turned NW, as if to follow the arcuate circumcaldera fault system. At the NW end of this dogleg, the fissure intersected a circumcaldera fault, and a small isolated vent erupted weakly at the top of the fault scarp.

Figure (see Caption) Figure 10. Preliminary map of Kīlauea caldera, showing the April and September lavas (stippled areas) and eruption fissures (cross-hatched lines). An isolated vent W of the September fissures is represented by a filled circle.

"The ENE-trending vents were fully active within about 3 minutes of the onset of the eruption and fountained vigorously and steadily through the night. General fountain height was estimated at 20-40 m, with Strombolian bursts that occasionally went as high as 50-70 m. Lava, fed primarily by these vents, rapidly filled a broad graben. At about 1930 the lava spilled southward through a gap in the caldera wall and fed an actively flowing channel that eventually extended more than 1.5 km to the S. Between 2100 and 2200, NE-flowing lava spilled into the interior of the caldera.

"The NW-trending vent segment was first recognized at about 1900. It extended NW to the caldera wall, which it reached at about 1945. The northwesternmost vent, on a segment of the caldera rim, opened at about 2100, and a small graben about 7 m wide and 20-40 cm deep extended E and W from the vent. The NW part of this line of vents had largely ceased erupting by 2300, but all other vents erupted with unchanged vigor until about 0500 on 26 September. At that time, the color changed from the normal yellow to an orange cast, and by 0600 most of the vents had shut down. Diminution of fountaining closely followed a marked decrease in tremor amplitude and a change in summit tilt from slow decrease to slow increase (see below). For the remainder of the eruption the only active vent was one in the central or S part of the NW-trending vent alignment. By 0830, eruption of new lava was about over, but loud explosive gas bursts continued until 0940.p>

"After the eruption was over, lava from the interior of the extensive pond surrounding the main vents drained back into the vents until 1800 on 27 September. The resulting collapse of the pond surface left a bathtub `ring' on the order of 2-4 m high on the enclosing escarpments. An early estimate suggests that perhaps as much as 3-4 x 106 m3 of pahoehoe lava was erupted. Of this, possibly as much as 1-2 x 106 m3 drained back into the vent system.

"Temperatures measured during the eruption were approximately 1,140-1,145°C for flows (pahoehoe toes and lava channels), 1,130-1,160°C for the NW-trending line of vents (cooler to the NW), and 1,170°C for the main, ENE-trending, vents. The latter vents fountained more vigorously, almost certainly erupted much more lava, were hotter, and emitted far more gas than the vents on the NW alignment.

"Gases from the erupting vents had atomic C/S ratios of 0.08-0.11 indicating considerable degassing of the magma prior to eruption. The gases were different from those of the 30 April 1982 eruption, which had a higher C/S ratio and were more oxidized. Hand lens inspection shows the new basalt to be almost aphyric. Olivine microphenocrysts are rare."

Kīlauea's small eruption of 30 April-1 May, also within the caldera, was from fissures roughly 1.5 km N of the September vents.

Seismic activity. "Earthquakes related to the eruption were centered in the S summit area (figure 11), initially forming a NE-trending epicentral zone 3.5 km long. Hypocenters were concentrated in a zone ranging from about 0.5 to 4.0 km in depth (figure 12). Located earthquakes ranged from 0.5 to 3.6 in magnitude. Several dozen were felt in the summit region. Nearly 100 earthquakes were located from the pre-eruption swarm, which started at 1650 when small earthquakes and weak harmonic tremor began to record on the summit seismographs. The seismic activity intensified rapidly so that within a few minutes stations 50 km away registered the signals and the number of recorded earthquakes reached 2-5/minute. For the first 3/4 hr, the onset of earthquake activity migrated from SW to NE at a rate of about 4 km/hour (figure 13). Moderate-sized earthquakes continued repeatedly along the entire epicentral zone until the eruption began, when earthquake activity in the S caldera region virtually ceased and strong harmonic tremor started. During the eruption, detectable earthquakes were smaller and less numerous than during the pre-eruption swarm. By midnight, locatable earthquakes had decreased to about 10/hour and were mainly confined to the NE part of the seismic zone.

Figure (see Caption) Figure 11. Map of Kīlauea caldera, with epicenters of earthquakes recorded 25-26 September. September eruption fissures are shown as cross-hatched lines and an isolated vent just to the W is represented by a filled circle.
Figure (see Caption) Figure 12. Depths of 25-26 September earthquakes projected into line A-A' from figure 11. The position of the eruption fissures along A-A' is represented by a cross-hatched line above the horizontal scale.
Figure (see Caption) Figure 13. Space-time diagram of earthquakes projected along line A-A' from figure 12, showing migration of epicenters from SW to NE at about 4 km/hour early in the pre-eruption swarm.

"Tremor intensity remained fairly steady through most of the eruption, but declined sharply between 0400 and 0500 on 26 September. By 0500, the tremor amplitude had declined almost to threshold level. As the eruptive activity waned during the morning of 26 September, earthquake activity renewed in the NE part of the seismic zone. Intermittent swarms accompanied minor surges of inflation indicated by summit tiltmeters. Post-eruption earthquakes occurred vigorously for much of 26 September and activity decreased slowly over the next 2 days. As of the end of September, the number of microearthquakes beneath the summit and upper E rift remained higher than average.

Deformation. "As in the April eruption, a rapid increase in summit tilt, probably related at least in part to emplacement of the feeding dike, coincided closely with the pre-eruption earthquake swarm. Uplift had reactivated old cracks by the time (1715) the first observer arrived near the site of the eventual outbreak. The recorded change in tilt on the upper NW flank was about 30 µrad, down to the NNW (figure 14). Termination of the rapid increase in tilt coincided approximately with the onset of strong harmonic tremor and the first appearance of lava. Most of the vigorous phase of the eruption was marked by gradual summit deflation. However, the tilt reversed at about 0450 on 26 September and the waning phase of the eruption was accompanied by gradual to moderate inflation that has continued intermittently since the eruption.

Figure (see Caption) Figure 14. E-W, top, and N-S, bottom, water tube tiltmeter records at Uwekahuna Vault, on the NW caldera rim. Large summit deflation in late June (at left) accompanied an intrusion into the SW Rift. The prominent inflation at right occurred mainly during the pre-eruption earthquake swarm 25 September 1982.

"A distance survey line across the zone where the new eruptive fissure formed was measured on 9 September, and repeated measurements were made during and after the eruption. Widening caused by the new dike was at least 705 mm and was accomodated in large part by contraction distributed across a broad zone on the flanks of the dike."

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: E. Wolfe, HVO.