Report on Kilauea (United States) — 25 August-31 August 2021
Smithsonian / US Geological Survey Weekly Volcanic Activity Report,
25 August-31 August 2021
Managing Editor: Sally Kuhn Sennert
Please cite this report as:
Global Volcanism Program, 2021. Report on Kilauea (United States). In: Sennert, S K (ed.), Weekly Volcanic Activity Report, 25 August-31 August 2021. Smithsonian Institution and US Geological Survey.
19.421°N, 155.287°W; summit elev. 1222 m
All times are local (unless otherwise noted)
HVO reported that a seismic swarm and ground deformation continued beneath the S part of Kilauea’s summit during 24-25 August. The rate of earthquakes per hour peaked at 28 during 1900-2000 on 24 August and then decreased to 5-12 through 25 August. Most of the earthquakes were between magnitudes 1 and 2, occurring at depths of 1-2 km. By 26 August seismicity and ground deformation levels had decreased, suggesting magma was no longer moving; HVO lowered the Volcano Alert Level and Aviation Color Code to Advisory and Yellow, respectively. Later that day, ground deformation began again in the S part of the caldera at around 1800 and was followed by an increase in seismicity after 2030. Earthquakes in the swarm were located at depths of 1-3 km. The strongest earthquake was a M 2.8, though the majority were less than M 1. The rate of events per hour was 16, with a peak of 24 just after midnight on 27 August, and then declined to about six. Seismicity remained low through 30 August with 7-8 events per hour, all under M 2 and at depths of 1-4 km. Deformation continued to be detected at variable rates. Although the deformation and seismicity suggested renewed magma movement, the data did not indicate an upward movement of magma.
Geological Summary. Kilauea, which overlaps the E flank of the massive Mauna Loa shield volcano, has been Hawaii's most active volcano during historical time. Eruptions are prominent in Polynesian legends; written documentation extending back to only 1820 records frequent summit and flank lava flow eruptions that were interspersed with periods of long-term lava lake activity that lasted until 1924 at Halemaumau crater, within the summit caldera. The 3 x 5 km caldera was formed in several stages about 1500 years ago and during the 18th century; eruptions have also originated from the lengthy East and SW rift zones, which extend to the sea on both sides of the volcano. About 90% of the surface of the basaltic shield volcano is formed of lava flows less than about 1100 years old; 70% of the volcano's surface is younger than 600 years. A long-term eruption from the East rift zone that began in 1983 has produced lava flows covering more than 100 km2, destroying nearly 200 houses and adding new coastline to the island.