"On 10-11 August seismographs and tiltmeters at HVO recorded a moderate intrusion at Kīlauea. The event was characterized by an earthquake swarm and harmonic tremor, accompanied by summit deflation and ground cracking. As of 0800 on 11 August, an estimated 30-50 x 10⁶ m³ of magma had intruded into the S summit and SW rift zones. The activity started with an increase of microearthquakes in the S summit area at 0330 on 10 August. Shortly before 0430 tiltmeters recorded the onset of the sharp summit deflation. By 0500 the seismic intensity increased and maintained a continuous state of activity. Micro-earthquakes and harmonic tremor less than 5 km in depth indicated that magma was migrating from the summit to the SW rift zone in the vicinity of the Kamakaia Hills nearly 20 km away. At mid-morning 11 August several thousand earthquakes of <= 4.5 Ms were detected, and monitoring instruments continued to record a diminishing pattern of seismicity and ground tilt."

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: R. Okamura, HVO.