The . . . eruption continued through March . . . . As of 1 March, lava stopped entering the ocean from the E part of the tube system. For the rest of the month, all activity was from the W tube system, which fed flows into the ocean along 2-4 fronts straddling Kupapau Point. Littoral explosions continued from at least two of the flow termini. At the main terminus, the explosions were continuous, producing a half cone or littoral rampart. This feature showed little vertical growth during the month, because flows continued to extend the shoreline, and the combination of wave erosion and settling caused parts of the cone/rampart to collapse.

A new black sand beach, 1.5 km long by 25-30 m wide, has formed from the pulverized volcanic glass produced by the explosions. Ocean currents carried the sand ~4.5 km from the tube system and have deposited it where there had formerly been low cliffs. A few very minor lava breakouts from the tube system occurred within a few hundred meters of the shore and upslope on the prominent S-flank fault scarp, but only lasted a few hours. The level of the lava pond over the active vent remained 9-15 m below the rim through March. The large surface overflows of late January-early February built up the walls of the pond by ~4-5 m, mostly on the lower N edge, but did not significantly change the height of the surrounding lava shield.

Harmonic tremor continued . . . near the eruptive vent site and Pu`u `O`o. Tremor amplitude varied between scattered gas piston activity with short interval changes, banded tremor with regularly spaced changes ½ hour to several hours apart, or a steady state sustained for many hours. Long-period events and tremor occurred intermittently beneath Kīlauea's summit in bursts that were sustained for a few hours to several days. The number of shallow earthquakes was generally below average beneath the summit and East rift zone. Some intermediate depth earthquakes occurred along the S flank of Kīlauea. A series of moderate-sized earthquakes occurred offshore 40-50 km NW of Keahole Point. Activity was initiated by M 5-5.5 shocks on 24 and 27 March that were widely felt on the islands of Maui, Oahu, and Hawaii. During the rest of the month, several dozen events in the same area had magnitudes of 2.5-4.

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.