The eruption . . . continued with little change . . . . Lava . . . traveled through the tube system and entered the ocean on the W side of Kamoamoa delta along a 350-m-wide front. The ocean entries were moderately explosive, forming small littoral cones on the bench.

On 1 December, a surface flow broke out above 610 m asl. The pahoehoe/aa flow descended ~500 m, then stagnated the following day. Breakouts from the lava tubes occurred again toward the end of the month, producing surface flows at 640 m elevation on 21 December, and a larger flow extending 400 m at 580 m elevation on 29 December. On 24 December a small breakout occurred at lower elevations on the coastal plain. Motion of each of the flows lasted <24 hours. A small skylight formed on the coastal plain on 20 December; lava upwelled in this breach several times before plugging it up.

Explosive activity at the ocean entries on 8 December deposited molten spatter onshore at the edge of the active bench. The lava benches at the W Kamoamoa entry continued to grow and extended almost 35 m into the ocean after the 26 November collapse of the old lava bench. The active bench area remains unstable and small collapses take place frequently.

The lava pond at the bottom of Pu`u `O`o crater remained active during the month, at a depth of 84 m below the crater rim. A new collapse area, 35-40 m in diameter and 15 m deep, was discovered at the E-53 vent. The pit engulfed all but the southern third of the E-53 spatter cone.

Microearthquake activity increased dramatically during the early part of the month from levels of 40-50 events/day to nearly 200 events on 9 December and >150 earthquakes the next day. Seismicity quickly dropped to prior levels in the early morning hours of 11 December. In the late evening of the following day, a swarm of long-period earthquakes began beneath the summit region. During 12-16 December, over 500 events (5 >=M 3.0) were counted and several were clear enough to be located. Another M 3.3 event preceded this swarm on 6 December, and was located 23 km beneath the NW flank of Mauna Kea.

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. Mattox and P. Okubo, HVO.