The August lava flows continued to advance through 20 September, mostly on top of older flows on the coastal plain. A small amount of national park land was newly covered with lava (on the coast side of Chain of Craters Road) but no more of the coastal highway was overrun. Lobes of the lava flow approached the Royal Gardens Subdivision access road and another small lobe reached the high tide zone but stopped before it entered the ocean.

On 20 September the tube system became blocked on the upper slopes and flows stopped. The next day, a new flow broke out above the top of the fault scarp (pali) at ~365 m elevation, moved W, and by the 25th had destroyed one house along the E edge of Royal Gardens at ~50 m elevation. The flow continued to advance through the SE corner of the subdivision, and by 1 October had destroyed seven houses, raising the total destroyed to 55 since . . . January 1983. The temporary access road to the housing area was overrun by lava on 5 October, and lobes continued to cover older lava flows and the flat coastal plain (figure 52).

The estimated output of lava . . . remained steady at 500,000 m³/day. Some brief overflows occurred at the lava pond, mostly in conjunction with blockages in the tube system.

Harmonic tremor persisted . . . at the active vent and near Pu`u `O`o. Microshocks associated with structural adjustments at Pu`u `O`o occurred intermittently during the month. Short bursts of deep tremor lasting less than several hours occurred along the magma conduit system in the eastern part of Kīlauea. Most earthquake activity was distributed broadly along the S flank as well as the summit region, and in the Kaoiki area along the SE flank of Mauna Loa.

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.