Episode 45 (E-45). Episode 45 . . . began 7 May at 1645 with typical intermittent lava spillovers. Continuous high fountaining started at 2240, and lava flows exited from both spillways formed during the previous phase. The NE flows extended a maximum of 2 km and those to the SE ~4.5 km, mostly on top of previous flows. Some short flows advanced to the N and NW, forming a broad fan at the base of the cone. The "1123 cone" observation post was again surrounded by flows.

High-amplitude tremor began on 7 May at 2242, almost simultaneously with the loss of 10.8 µrad. By the end of the month, the summit had regained 12.4 µrad of inflation (figure 43).

Episode 46 (E-46). During the afternoon of 1 June intermittent lava fountains were reported at Pu`u `O`o. Continuous fountaining began 2 June at 0230 and ended at 1327. High-amplitude harmonic tremor began at 0240 and declined to background levels at 1309. Summit deflation totaling 11 µrad began on 1 June at 1200 and stopped the next day at 1700, 3.5 hours after lava production ended. Lava flowed through both the NE and SE spillways, extending a maximum of 5 km SE.

A series of very high fountain jets started at 1041, 2¼ hours before the end of the episode. Jetting lasted from several seconds to about a minute, then died back briefly before fountaining resumed. Similar fountain jets were observed during E-42 on 23 February.

After E-46, the summit of Pu`u `O`o was 255 m above the pre-1983 surface, a growth of only 5 m since the end of 1985. The cone was steep and the many short flows on the flanks were widening the base.

Since E-40 on 1 January, the eruption recurrence interval has been very regular, ranging from 22 to 26 days.

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: C. Heliker, R. Koyanagi, and R. Hanatani, HVO.