HVO reported that localized earthquake and ground deformation rates in around Kilauea’s upper East Rift Zone significantly increased twice during 22-23 July. The Volcano Alert Level was raised to Watch (the third level on a four-level scale) and the Aviation Color Code was raised to Orange (the third color on a four-color scale) at 0406 in response to the increases, and then lowered back to Advisory and Yellow, respectively, at 0904 because of a significant decrease in the activity; seismicity and ground deformation rates remain elevated but at a lower intensity. Pulses of increased seismicity were detected during 24-25 July; over 500 earthquakes were recorded, including 12 events with magnitudes greater than 3. Seismicity rapidly decreased to normal levels by midday on 25 July and remained at low levels through 30 July. Minor deformation was detected.

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)