During January, an estimated 70% of the lava that emerged from the Kupaianaha lava pond entered the ocean via the W tube system . . . . The pond level averaged 20-25 m below the rim all month. Two flows that branched from the main tube system at 440-425 m completely roofed over during the month but fed surface breakouts at low elevations. The terminus of the first flow was near the N edge of the 1986 Kapa'ahu kipuka at 35 m elevation. The second flow followed the E edge of the 1986-89 lava field during early January. By the 23rd, the main terminus had advanced onto grassland and was 800 m upslope of Hwy 130. The 150-m-wide terminus did not advance after the 23rd, but the flow remained active upslope. Active lava was also sighted several times in the bottom of Pu`u `O`o.

Output from the tube system at the coast continued to build an active lava bench, which measured 535 x 115 m on 5 January. Lava entered the bench at one main entry point and at two smaller outlets to the E. From 5 to 9 January, 20% of the bench was destroyed by small collapses. On the 11th, a steam jetting event from the tube on the bench deposited spatter 150 m inland. On the 20th, three littoral cones (~1-2 m) were forming on the bench. A major collapse on the 23rd at 0844 removed the bench's W half, causing an explosion that threw 10-50-cm blocks 40-50 m inland. On 24 January, spatter explosions built cones 2 m high on the remaining portion of the bench, which began to rebuild on the 26th. Growth continued until the end of the month.

Low-level tremor . . . continued in the middle East rift zone and at the flow front near Kupapau Point. Tremor was generally steady except 5-9 January when amplitude fluctuated at intervals varying from minutes to several hours. A series of rockfall and acoustic signals, caused by the major bench collapse on 23 January, was recorded . . . from 0820-0948. The number of microearthquakes was about average in the summit region and 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.