The eruption began just before midnight on July 5 and involved fissures extending across the length of Moku‘āweoweo, Mauna Loa's summit caldera, and into the upper ends of the volcano's northeast and southwest rift zones.

[2] No unusual activity was noted on the Mauna Loa seismograms during the early evening of July 5; seismicity was at relatively low levels.

At 23:18 HST, however, seismic alarms, signifying prolonged high-amplitude volcanic tremor, were activated in homes of Hawaiian Volcano Observatory (HVO) staff.

Hawaiʻi Volcanoes National Park and civil defense authorities were alerted to the imminent probability of a Mauna Loa eruption.

A light airplane with two HVO staff members aboard reached the summit area on July 6 at 01:48 HST; a line of lava fountains 66 to 164 ft (20 to 50 m) high crossed the entire floor of Moku‘āweoweo at this time and extended about 0.62 mi (1.00 km) down the southwest rift zone.