EPISODE 6

"Kīlauea's E rift zone eruption was in its sixth episode from 21 to 25 July. The episode 6 eruptive vent was the same spatter cone, approximately 750 m NE of Pu'u Kamoamoa, that was the major source of episode 4 and 5 lavas (figure 19). Between eruptive episodes the vent contained incandescent cracks and continued to emit magmatic gases.

"The first episode 6 eruptive activity was seen from a passing aircraft at about 0600 on 21 July. From then until midafternoon the next day, extrusive activity consisted of cyclic filling and draining of the funnel-shaped interior of the spatter cone. Fountain activity at this stage ranged from intermittent bursts of spatter to the more steady play of a 3-4-m-high dome fountain.

"At approximately 1530 on 22 July, the pond filled to a depth of about 20 m, and lava spilled over low places on the rim of the spatter cone to begin feeding flows to the N, NE, and SE. Lava production rapidly increased, and a major aa flow advanced NE, fed by a vigorous pahoehoe river issuing from the pond at spillways on the N and NE flanks of the cone. Blocked from advancing SE by flows and vent deposits of earlier episodes, this flow moved ENE through the rain forest on the N side of Pu'u Kahaualea. During the period of greatest lava discharge, estimated on 24 July at about 0.25 x 10⁶ m³/hour, the flow advanced at more than 200 m/hour. Ultimately it extended 6 km from the vent, covering an area of about 2 x 10⁶ m² with a volume on the order of 10 x 10⁶ m³.

"During the period of active lava flow production, a fountain played continuously from the surface of the pond within the vent. The fountain was at its most vigorous on 23 July, when it often reached heights ranging from 50 to 150 m. It produced flows of spatter-fed pahoehoe and a local tephra blanket that extended SW from the vent. Subsequently the fountain was less vigorous and 30-60 m high, approximately 1.5 times its height at the end of episode 5.

"Lava temperatures measured by thermocouple ranged from 1128°C on 22 and 23 July to 1138°C (a new high temperature for the 1983 eruption) on 24 July. Hand-lens inspection indicated that episode 6 basalt contains scattered small phenocrysts of plagioclase and olivine. Thus, it generally resembles, except for the more olivine-phyric basalt of episode 5, the earlier 1983 lavas.

"Harmonic tremor, which had persisted at a low level after the end of episode 5 eruptive activity on 3 July, began to fluctuate slightly and increase gradually during the period of cyclic filling and draining of the lava pond on 21 and 22 July. Shortly before 1600 on 22 July, tremor intensity increased rapidly in concert with increasing eruptive vigor. Tremor reached a high level at about 1800 and maintained it through the 3-day period of strong effusion. At about 1620 on 25 July, tremor decreased rapidly as the eruption came to an end. Low-level tremor, like that characteristic of other inter-eruptive periods, has continued in the vent area since 25 July.

"The Uwekahuna water-tube tiltmeter recorded about 17 µrad of summit deflation during episode 6. Following gradual inflation that had been underway since the end of episode 5, the summit of Kīlauea began to deflate at about 1600 on 22 July, approximately coincident with the increases in tremor amplitude and lava emission. Summit deflation increased to a maximum rate of 3-4 µrad/hour on 23 and 24 July. The rate decreased thereafter until about 1800 on 25 July. Since then the summit has been gradually reinflating."

Addendum: Eruptive activity resumed at the episode 6 vent on 15 August. Harmonic tremor increased at approximately 0700; lava fountains 20-30 m high and a 1 km-long lava flow to the NE were reported by field crews that arrived at the vent at 0845. At press time on 17 August, Tina Neal reported that lava fountains had decreased to 5-10 m high, the lava flow extended about 6 km NE with lobes both N and S of the episode 6 flow, and summit deflation continued.

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, A. Okamura, R. Koyanagi, and T. Neal, HVO.