A shallow earthquake swarm began in the summit region at about 1730 on 9 December. Epicenters soon migrated into the upper E rift, to the vicinity of Lua Manu and Kokoolau Craters (1.4-3.2 km from the caldera rim). Preliminary locations indicate depths from 0.5 to less than 4 km beneath the surface. The largest earthquake had a magnitude of 3.5. No harmonic tremor was recorded.

Tiltmeter records from the NW caldera rim (Uwekahuna Vault) showed slow deflation starting about 1730 and accelerating about 1830. Just before 2000, the deflation rate decreased, and by 2030 slow inflation had resumed. Total deflation was about 5 µrad, suggesting that 2 x 10⁶ m³ of magma from the summit chamber was intruded into the E Rift.

As of early 10 December, earthquake counts were slightly elevationated in the swarm area and slow summit inflation was continuing. This event marked Kīlauea's 17th intrusive event since the magnitude 7.2 earthquake of November 1975. Four eruptions have occurred since the 1975 earthquake.

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.

Information Contacts: E. Wolfe, HVO.