During 18-21 July, the E vent and dominant W vent in Kilauea's Pu'u 'O'o produced lava flows. On 18 July, new vents opened in the Puka Nui pit, in the SSW area of Pu'u 'O'o crater, and produced lava flows that ponded. On 20 July, a vent high on the S crater wall, adjacent to the Puka Nui Gap pit, produced spatter and propelled lava bombs 10 m into the air. Meanwhile, the lava lake in the West Gap pit continued to fill, overturn, and occasionally overflow. The spatter cone that built up around the S wall vent in West Gap pit was submerged beneath the lava lake surface on 20 July. Uplift of the crater interior continued. Earthquakes occurred beneath the upper E rift zone, S flank, and Halema'umau crater.

On 20 July, just before midnight, Pu'u 'O'o's crater floor started to subside; a tiltmeter recorded a nearly 300 microradian tilt change. Just after midnight, on 21 July, the West Gap lava lake and Puka Nui pit drained. A new eruption initiated along a set of fissures that extended 1.7 km E from a point about 150 m E of the E rim of Pu'u 'O'o crater. Preliminary reports described two 600-800 m long, left-stepping fissures between Pu'u 'O'o and Kupaianaha. The easternmost fissure fed two lava flows; the farthest extent of the flow was 1-1.5 miles from the fissure in the SE direction.

On 22 July, HVO reported that the westernmost fissure was inactive by mid-morning on 21 July and the uppermost segment of the active lower fissure was completely sealed by mid-morning on 22 July. The rest of the fissure erupted lava, constructing several small perched ponds. A perched pond at the upper segment of the active fissure breached and produced an a'a' flow that traveled 300-400 m to the E. At Pu'u 'O'o crater, several new cracks were observed around its rim, parts of which had collapsed. During 23-24 July, lava ponds surrounding lower fissure segments grew in thickness and spilled lava over their edges.

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)