During 21-27 December, HVO reported that the lava lake circulated and periodically rose and fell in the deep pit within Kīlauea's Halemaʻumaʻu Crater, remaining below the inner ledge (75 m below the crater floor). Almost daily measurements indicated that the gas plume from the vent continued to deposit variable amounts of ash and fresh spatter nearby. On 22 December the SW vent wall collapsed into the lake, ejected lava onto the inner ledge, and caused an increased amount of ash in the plume.

Incandescence was visible from small spatter cones on the E and S edges of the Puʻu ʻŌʻō crater floor. Pāhoehoe lava flows, that were 300-400 m wide and fed by lava tubes from the fissure, continued to be active about 6.8 km SE of Puʻu ʻŌʻō and entered the ocean W of Kaʻiliʻili. During 25-26 December the tube appeared to be more robust and less surface flow activity was reported. Small plumes were observed from the ocean entry during 22-24 December and infrequent weak plumes were observed during 25-26 December. On 27 December a breakout of lava flows were visible on the pali (a fault scarp).

Source: US Geological Survey Hawaiian Volcano Observatory (HVO)

Geological Summary. Kīlauea overlaps the E flank of the massive Mauna Loa shield volcano in the Island of Hawaiʻi. 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 Halemaʻumaʻu 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.