Lava continued to flow into the ocean E of Kupapau Point, and [13] May marked a full year of lava entry into the ocean through the W tube system. Surface lava breakouts were numerous from two areas (420-450 and 120-150 m elevation) of the W tube system. A surface flow that formed in April at 120 m elevation had reached the coast by 4 May and remained active until the [9th]. The flow added to the E half of the active seacoast lava bench, bringing the bench's dimensions to 500 x 50-70 m. On the 25th, the only collapse of the month destroyed 70% of the bench. The collapse was witnessed by two geologists who saw areas as large as 100 m long and 10 m wide fall into the sea up to one-half hour after the initial collapse. Small littoral explosions accompanied the collapse.

Lower-elevation breakouts also produced pahoehoe flows that moved around the SE corner of the Royal Gardens kipuka and continued onto the coastal flats, forming a broad area (~600 m wide) of activity. By 29 May, the lava front had advanced to within 30 m of the coast and stagnated, but activity continued upslope. The surface flows that formed by breakouts above the fault scarp in April remained active in the Royal Gardens subdivision, destroying four houses (on 15, 21, 23, and 27 May) and blocking normal access to remaining structures. East of the subdivision, a flow blocked a major access road in the . . . National Park on 6 June. Active flows were 600 m NE of, but did not directly threaten, the Wahaula visitor center. Some flows advanced over grassland, starting small fires. The central and E tube systems (drained in April) remained inactive in May. The surface of the Kupaianaha lava pond was 23-25 m below the crater rim during the month . . . . Spattering and small sporadic lava ponds were intermittently observed in Pu`u `O`o crater.

Low-level seismicity continued beneath Pu`u `O`o and Kupaianaha during May. Relatively steady tremor beneath Pu`u `O`o was occasionally interrupted by variable-amplitude signals associated with temporary increases in crater bottom activity. Occasional rockfall signals from Pu`u `O`o and flurries of small high-frequency shocks near Kupaianaha were also recorded. The Wahaula seismic station continued to detect a variety of low-amplitude signals generated by lava entering the sea. The number of shallow (<5 km) microearthquakes was relatively low in the summit region and East rift zone. Episodic bursts of intermediate-depth (5-13 km) events and tremor occurred beneath the summit region. Fourteen relatively large earthquakes (M 2.5-3.9) were recorded . . . during 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: C. Heliker and R. Koyanagi, HVO.