HVO reported that the eruption located at the W side of the down-dropped block within Kilauea’s Halema`uma`u Crater had ceased after activity declined over a few days. During 12-14 September multiple active vents, that were roughly E-W-trending and spanned a distance of about 750 m, produced lava fountains that rose as high as 10 m. Ramparts built by spatter were almost 20 m tall on the S sides (downwind side) of the vents. Lava from the vents flowed onto the N and W parts of the crater floor on 12 September, onto the N and E parts on 13 September, and only onto the W part by 14 September; the distances of the active flows progressively decreased. The area N of the active vents had become perched and was 3 m higher than the surrounding surface. Sulfur dioxide emissions averaged 20,000 tonnes per day (t/d) on the afternoon of 13 September, down significantly from 190,000 t/d measured just after the onset of the eruption. Effusion rates had decreased but remained at high levels.

Vigorous spattering and lava fountains that rose 10-15 m were visible at the westernmost large spatter cone during 14-15 September. Minor spattering at the next cone to the E did not rise above its rim. Lava continued to flow from the vents and travel N and W, confined to the W part of the down-dropped block and the NE parts of Halema`uma`u. A laser rangefinder pointed at the W portion of the crater continued to record uplift from the magmatic intrusion beneath the caldera since the onset of the eruption; the total local uplift was 6 m by 13 September, 9 m by 14 September, and 10 m by 15 September. Field crews observed that eruptive activity had greatly diminished or ceased at several of the vents by the morning of 15 September. Lava was no longer flowing onto the crater floor but active lava was ponded in an area N of the vents. Intermittent spattering was visible overnight at the large, westernmost cone but beginning at around 0700 on 16 September webcam images recorded minor to no fountaining. By 1115 spattering ceased and by noon the ponded lava had stagnated. Tremor levels indicting fluid movement decreased during 15-16 September and retuned to pre-eruption levels by 1700 on 16 September. Sulfur dioxide emission rates had also decreased and were 800 t/d by 16 September, only slightly above the 100-200 t/d typical of non-eruptive periods. At 0902 on 17 September HVO lowered the Volcano Alert Level 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).

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)