. . . lava production continued through early April, advancing through tubes and entering the ocean at three sites on the W side of the flow field (figure 77). A lava bench, built by the two eastern ocean entries since autumn 1990, was 125 m long and extended ~30 m into the sea in early March. A new bench then began to grow 2-3 m below the older bench, and was over half its length by mid-March. Significant erosion at the E end of the older bench culminated in its partial collapse late in the month, causing lava to pour into the ocean from beheaded tubes and large surface flows. The W entry remained quite explosive as its fragile lower bench collapsed frequently. A littoral cone on the old sea cliff was >3 m high by the end of March, and > 90% of its surface was covered by spatter. A long-lived surface flow on the W side of the lava field continued to advance slowly through the remnants of Royal Gardens subdivision. No surface flows or breakouts from the still-hot tube system have recently been observed on the E side of the lava field, where numerous homes had been destroyed in the Kalapana area.

Through the first half of March, many shallow long-period earthquakes or tremor events continued . . . beneath the caldera at 0-5 km depth. Since beginning in late December, the long-period activity had shown representative rates of >2,000 events/day, but in March it appeared to alternate with other summit seismicity. As shallow long-period activity started to decline 10 March, short bursts of slightly deeper long-period seismicity were recorded, also beneath the summit but at 5-13 km depth. Two days of elevationated high-frequency summit microearthquakes followed, apparently terminating on 13 March with a short burst of intermediate-depth long-period events, then a return to high levels of the shallow long-period seismicity. A similar sequence occurred 19-22 March. After 22 March, however, the number of shallow long-period summit events fluctuated more than in previous months, as the summit deflated ~7-8 µrad by 26 March.

On 26 March at about 0532, a shallow (<5 km deep) earthquake swarm and magma intrusion started in the upper east rift zone (between Pauahi and Aloi craters), 6 km SE of the caldera rim and 15 km uprift of the active Kupaianaha vent. Sharp summit deflation began 5 minutes later, and another 7-8 µrad of deflation was registered at the summit by late the next day. New tiltmeters just downrift of the swarm area (at Pu'u Huluhulu) also measured rapid deflation to the SSE, totaling ~40 µrad. Intense seismic activity continued for ~3 hours before tapering off, although upper east rift seismicity remained elevationated through the end of the month.

The seismicity was apparently associated with collapse in Pu`u `O`o crater, ~12 km downrift, where a new blanket of red dust extended 2 km SW of the cone on 26 March. Collapse episodes have been common at Pu`u `O`o in recent years, substantially increasing the diameter of the crater. A lava pond on the crater floor remained active in March. As of early April, the lava pond and its overflows covered the entire crater floor, and small intermittent lava fountains were observed in the pond.

The swarm and intrusion occurred near the intersection of the East rift zone with the ENE-WSW-trending Koae fault system, which passes S of the summit and connects the East and Southwest rifts. The resulting East rift/Koae/Southwest rift system forms the linear boundary zone between Kīlauea's mobile S flank and the rest of the volcano.

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: T. Moulds and P. Okubo, HVO.