During 10-17 December, lava continued to enter the sea at several points along the coast. On 15 December, shortly after 0700, the Wilipe'a lava delta partially collapsed, losing about 1/3 of its area. The tip of the delta retreated shoreward about 260 m and most of the collapse was in the central part of the delta. Around the 15th and 16th a substantial collapse occurred at the West Highcastle delta. Generally, seismicity was at normal levels. The swarm of long-period earthquakes and tremor beneath Kilauea's caldera, occasionally seismically active since June, continued at a relatively low level. The Pu`u `O`o tiltmeter showed deflation for about one week until the 17th. No other significant deformation was recorded.

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.

Source: US Geological Survey Hawaiian Volcano Observatory (HVO)