Hawaiian Volcano Observatory (HVO) reported that the eruption at Kilauea which began on 15 September from fissures to the W of Napau Crater and on the crater floor continued during 17-19 September, and then paused on 20 September. The eruption area is located in a remote section of the middle East Rift Zone. The opening of new fissures on the Napau Crater floor during 0400-0500 on 17 September was detected using infrasound signals, a thermal anomaly identified in a GOES satellite image, and webcam views. During an overflight later that morning, scientists observed lava fountaining 10 m high along the fissures and lava flows advancing on the crater floor. The activity was vigorous but had started to wane by the afternoon. During an overflight on the morning of 18 September, volcanologists observed only minor activity on the crater floor. Only one vent was active and produced low lava fountains in a tiny pond, and there was some residual movement of lava along a margin of the flow field. A small new flow at the W end of the fissure system was inactive. Steam-and-gas continued to be emitted from the fissures to the W of the crater that had opened on 15 September.

New fissures opened W of the crater at around 1515 on 18 September. Flows from lava fountains along the fissure rapidly advanced E and cascaded down the NW wall of Napau Crater onto the crater floor. Sulfur dioxide emissions averaged 10,000 tonnes per day, associated with the opening of the new vents. The lava falls continued overnight during 18-19 September and by around 1000 on 19 September about one-third of the crater floor, or approximately 250,000 square meters, was covered by lava. The amount of coverage suggested that the lava effusion rate was 5-15 cubic meters per second during the most active phase. Activity greatly diminished overnight; the lava channels and falls began to crust over by 2000 and during 2100-2200 they had completely crusted over. Strong incandescence from the vent began to decrease around 0230 on 20 September. Field crews observed minor spattering and small fountains at one end of the vent at around 0830, but by 1000 no activity was seen, and the eruption had paused. In total lava flows covered about 63 hectares (630,000 square meters) of Napau Crater and areas to the W.

At 0812 on 23 September the Volcano Alert Level was lowered to Advisory (the second level on a four-level scale) and the Aviation Color Code was lowered to Yellow (the second color on a four-color scale). HVO noted that observations and instrumental data since the pause in the eruption indicated that the potential for renewed eruptive activity had declined. Seismicity in the area was extremely low and no tremor was being recorded. Deformation data showed that magma movement to the middle East Rift Zone has slowed dramatically or stopped altogether. Volcanic gas emissions decreased to near background levels.

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)