During 20-26 June, incandescence was not visible from the vents in Kilauea's Pu'u 'O'o crater. A tiltmeter at Pu'u 'O'o continued to show steady tilting inward toward the crater, and the crater floor was estimated to have subsided 100 m between 17 and 21 June.

On 19 June, new ground cracks were discovered in an area west of Mauna Ulu. On 20 June, HVO scientists measured sulfur dioxide concentrations greater than 10 parts per million (ppm) in a broad area adjacent to Halema'uma'u crater. Typical concentrations are generally negligible except for areas downwind of Halema'uma'u crater, where they can get up to 2.5 ppm in narrow zones. On 21 June, scientists confirmed that lava was not entering the ocean at the Poupou entry.

During 21-26 June lava was not visible anywhere on the flow field or at the site of the 18/19 June eruption. The crack W of Kane Nui o Hamo continued to emit steam and fume. The summit area continued to inflate very slowly and seismic tremor values at Pu'u 'O'o were below pre-June 17 levels. On 25 June, sulfur dioxide and carbon dioxide emissions were at approximately pre-June 17 levels after a gradual decline. HVO lowered the Volcanic Alert Level from Watch to Advisory and Aviation Color Code from Orange to Yellow. Aerial observation revealed that steaming from the site of the 18/19 June fissure eruption decreased, though the steaming cracks at the base of Kane Nui o Hamo were vigorously fuming. Ground-based mapping of the new lava flow was also completed; the eruption occurred from two places along the fissure, separated by about 40 m.

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)