EPISODE 32

"The 32nd episode of the 1983-1985 eruption occurred on 21-22 April, following 38 days of repose. Intermittent dome fountaining began at 1516 on the 21st and lasted for about 4 hours. Continuous fountaining and lava production commenced at 1804. By 1910, tremor amplitude had increased and vigorous lava fountaining had begun. A broad aa flow advanced SE and split into 3 lobes about 3-4 km from the vent. The central lobe advanced the farthest, passing W of Royal Gardens subdivision, and stagnated 6 km from the vent (figure 35). Lava fountaining ceased at 0906 on the 22nd.

Figure 35. Lava flows erupted from Kīlauea between January 1983 and 22 April 1985. The episode 32 flow is shown by diagonal lines. Courtesy of HVO.

"Heavy tephra fallout added 9 m to the elevation of Pu`u `O`o (a name recently suggested by local elders to replace the previously used Pu'u O') and blanketed the area SW of the vent. The summit collapsed 5 m during the following week.

"At the end of April, the cone was 928 m above sea level and 209 m above the pre-1983 surface. The total volume of lava produced through episode 31 was 354 x 10⁶ m³, slightly exceeding the total reported for the Mauna Ulu eruption of 1969-74.

"Kīlauea remained quiet through the end of April. Heavy fume obscured the view into the vent, and the magma column was not observed.

Deformation. "The summit of Kīlauea subsided rapidly during the 32nd episode of the eruption. The Uwekahuna (W-E) tiltmeter recorded continuous summit subsidence from 1700 on the 21st until 1100 the next day, about 2 hours after fountaining stopped. The maximum rate of subsidence occurred between 2200 and 2300 on 21 April and measured nearly 2.1 µrad per hour. The net tilt change was 17.0 µrad. Reinflation of the summit had reached 6 µrad by the end of April.

Seismicity. "Harmonic tremor in the middle E rift zone near Pu`u `O`o increased gradually from about 1516 on 21 April, when intermittent dome fountaining began. Starting at 1843, tremor increased rapidly to an order of magnitude above background and remained high for the duration of the eruptive episode. At 0903 on the 22nd, about the time that lava fountaining ceased, the tremor level decreased rapidly, and by 1240 the intensity was down to nearly background levels.

"Following episode 32, harmonic tremor continued near Pu`u `O`o in the characteristic pattern observed during previous interphase periods. The number of microearthquakes decreased to a low level in the summit region and E rift zone."

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: Episode 32 of 1983-85 middle E Rift Zone eruption