Kīlauea's . . . eruption continued in October, with lava entering the sea at the Kailiili, Poupou, and Kupapau Point entries. Surface activity was concentrated between the lower Royal Gardens subdivision and the Wahaula area. During the first week of October, lava covered an additional several hundred meters of the Chain of Craters road. The flow reached the sea at the W edge of the Kailiili entry on the 6th, extending the bench a few hundred meters W. A surface lava breakout near the SE corner of the Royal Gardens kipuka entered the sea on 12 October ~250 m E of the former entry E of Kupapau Point (inactive since 23 August). This new entry remained active for only a week. Surface activity at higher elevations included an intermittently active breakout at the 580 m elevation that built a small parasitic shield on top of older flows. A surface flow that extended from 180 to 120 m elevation remained active throughout the month.

The level of Kupaianaha lava pond averaged 21-23 m below the rim during October. Activity at Pu`u `O`o was sporadically observed for the first time in more than a month on 15 October. Periods of spattering alternated with episodes in which lava ponded and flowed in channels across the crater floor.

Eruption tremor continued near Pu`u `O`o and Kupaianaha in October. Days when tremor had relatively steady amplitude were interrupted by successive minor amplitude changes lasting from <1 to several hours. Bursts of increased signals at Pu`u `O`o were associated with rockfalls on the unstable cone. Pronounced longer bursts, lasting ~10 minutes on 11 and 13 October, were apparently also produced by rockfalls. Swarms of shallow high-frequency microshocks near Kupaianaha lasted less than an hour and occurred against a background of variable-amplitude tremor, notably on 8 and 26 October. Three seismic bursts on 23 October were related to partial collapse of Kupaianaha's pond wall. Weak intermittent signals from coastal lava flows entering the sea were detected . . . . Intermediate-depth (5-10 km) long-period events and weak shallow tremor (< 5 km) occurred episodically beneath the summit region. The number of microearthquakes throughout the month was about average in the summit region and along the East rift zone.

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: C. Heliker and R. Koyanagi, HVO.