HVO reported that a new eruption began in Kilauea’s Halema`uma`u Crater on 10 September following a period of increased seismicity. Seismicity increased on 22 August; most of the earthquakes were located at depths of 2-3 km and were all smaller than M2. About 150 occurred during 9-10 September. Tiltmeter and Global Positioning System (GPS) data showed inflation in the S portion of the crater.

At 0252 on 10 September HVO raised the Volcano Alert Level to Watch (the third level on a four-level scale) and the Aviation Color Code to Orange (the third level on a four-color scale) due to increased earthquake activity and changes in ground deformation that indicated magma moving towards the surface. An eruption commenced at about 1515 in the E part of the caldera based on field reports and webcam images. Fissures opened on the crater floor and produced lava fountains and flows. The Volcano Alert Level and Aviation Color Code were raised to Warning and Red, respectively. Gas-and-steam plumes rose from the fissures and drifted downwind. By 1900 the line of fissures was about 1.4 km long and extended into the E wall of the down-dropped block. Multiple active fountains were about 20-25 m high; fountains at the initial eruption onset were an estimated 50 m.

At 0810 on 11 September the Volcano Alert Level was lowered back to Watch and the Aviation Color Code was lowered back to Orange because the style of eruption and fissure location had stabilized, the initial extremely high effusion rates had declined (but remained at high levels), and no infrastructure was threatened. The eruption plume, mainly comprised of sulfur dioxide and particulates, rose as high as 3 km (10,000 ft) a.s.l. and had become less dense. Lava erupted from fissures on the down-dropped block flowed W towards Halema`uma`u, covering much of the surface with active lava as deep as about 2.5 m. During 11-12 September easternmost vents on the down-dropped block and the westernmost vents in Halema`uma`u became inactive; the active vents were E-W-trending and spanned a distance of about 750 m. Channelized lava flows traveled N and W onto the Halema`uma`u Crater floor, burying the E rim of the crater and most of the crater floor; higher older lava flows prevented movement onto the SW part of the floor. Lava fountaining continued, rising as high as 15 m by the morning of 12 September. A laser rangefinder pointed at the W portion of the crater recorded almost 5 m of uplift from the magmatic intrusion beneath the caldera since the onset of the eruption.

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)