Seismicity abruptly increased below Kilauea’s summit at about 1400 on 29 September. Around 30 minutes later the earthquakes became more intense, frequent, and shallower, and deformation patterns rapidly changed. The data suggested an upward movement of magma that prompted HVO to raise the Aviation Color Code to Orange and the Volcano Alert Level to Watch at 1509. A new eruption was identified at 1521 when incandescence from Halema`uma`u Crater became visible in webcam views; HVO raised the Aviation Color Code to Red and the Volcano Alert Level to Warning. Fissures opened along the bottom of Halema`uma`u Crater floor and produced lava fountains and flows. A photo taken at 1615 showed a large plume comprised of steam, carbon dioxide, and sulfur dioxide rising from the fissures. Measurements just after the eruption started showed sulfur dioxide emissions of around 85,000 tonnes/day. At about 1640 another fissure with several vents opened on the inner W wall of the crater and produced low lava fountains and flows that descended to the crater floor. The vent expanded by 1709. Lava from both fissures pooled on the solidified lava lake surface and quickly began to overturn and create a lava lake. Tephra was deposited in areas SW of the crater and collected by HVO scientists for analysis.

The tallest lava fountain was near the S end of the lava lake and rose 20-25 m during the night of 29-30 September. During a helicopter overflight around 0730 on 30 September scientists determined that the lake was about 980 m E-W and 710 m N-S, covering an estimated 52 hectares. The W wall vent was visible, and several fountains were rising from the fissure in the central part of the lake. Sulfur dioxide emission rates remained high, estimated at around 20,000 tonnes/day. Overnight during 30 September-1 October fountains rose as high as 15 m at the dominant vent in the W wall. Less vigorous fountaining persisted at other vents, though fewer were active. The lake had risen 24 m by the morning of 1 October, adding 4 m in the past day. Cooled and crusted parts of the lake’s surface overturned, or “foundered.” Sulfur dioxide emission rates remained high, estimated at around 12,900 tonnes per day.

The lake had risen another 2 m by the morning of 2 October; fountains were 7 m tall at the main W wall vent and 1-2 m at the southern vents. Fountains occasionally rose as high as 50-60 m in bursts. Pumice, Pele?s hair, and fragments of volcanic glass were deposited downwind. The sulfur dioxide emission rate on 3 October was again high at 14,750 tonnes/day. The W vent was again the most vigorous during 3-4 October with sustained lava fountains to 10-15 m with occasional bursts up to 20 m. The lake rose 3 m, past the base of the W vent where a 12-m-high spatter cone had formed, and continued to founder in spots. Lava fountains rose 5-10 m from the vents in the S and central portions of the lake, including along a fissure 35-42 m long, with occasional larger bursts. The lake was not level and generally higher near the location of the vents; the W end was 1-2 m higher than the E, and S end was about 1 m higher than the N. By 4 October ledges about 20 m wide separated the N and E parts of the active lava lake from the crater wall and were lower than the lake surface; the N, E, and S margins of the lake were perched about 3 m above the surrounding ledge. The sulfur dioxide emission rate remained elevated but had decreased to 7,000-9,000 tonnes/day. HVO lowered the Aviation Color Code to Orange and the Volcano Alert Level to Watch at 1652. On 5 October lava fountaining from the W vent was unchanged while fountains from the other vents rose 1-5 m. The lake rose 1 more meter.

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)