A fascinating magma intrusion event at Kīlauea on 8-9 February was unusually well documented. Continuously recording tiltmeters monitored a sharp summit deflation beginning 8 February at 1902, 5 hours after the start of an earthquake swarm (M 3-4) on the upper E rift zone. A local magnetic anomaly (approximately l0 gamma) also occurred in the upper E rift zone, and seismicity reached 200 events/hour with 3-7 km focal depths, but no eruption took place. Geodimeter surveys 1 day after the event showed extensions of up to 0.25 m across the upper E rift and electrical self-potential traverses add more documentation of magma migration. Similar events took place in June and July 1976, and HVO scientists suggest that magma is draining from beneath the summit area along subsurface paths created by the major earthquake of 29 November 1975. These drainage paths readily allow periodic intrusion into the E rift and are perhaps preventing major inflation of the summit reservoir.

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: Hawaiian Volcano Observatory, USGS.