Volcano Watch — Current eruption continuing at low levels

We will cover activity during the last two weeks, since we missed our deadline last week. The episode 51 vents on the west flank of Pu`u `O`o, which began erupting on Wednesday, June 10, shut down on June 16. The vents were then inactive until Sunday, June 21, and have continued to be active through June 26.

The eruptive period from June 10 to June 16 was characterized by rather low volume activity. For example, the perched lava pond surmounting the episode 51 lava shield took several days to fill, and nearly all the lava flowed through the pond and down a tube toward the south. A small spatter cone, called a hornito, formed above a weak point in another tube leading out of the pond, but was located on the north flank of the episode 51 shield. This hornito was the source of a small `a`a flow by June 13. On June 16, the eruption shut down, the pond drained, and the flows stopped advancing within a few hours.

The eruption restarted on the morning of June 21 and was much more vigorous than during the previous eruptive period. Within a few hours, the pond was overflowing, and large flows were advancing towards the north, west, and south of the vent area. As of Friday morning, the eruption is still continuing. The summit has deflated slowly but continuously throughout this eruptive period as more lava is erupting than is being resupplied to the summit from below. The rate of summit deflation had slowed by Friday morning, which may indicate that this eruptive period is nearly over.

The lava lake inside Pu`u `O`o was nearly level with the crater flow, at a depth of about 150 feet below the lowest rim of the cone, when lava began erupting from the episode 51 vent on June 10. By the following day, the lava lake level had dropped by about 30 feet. After the eruption stopped on June 16, the pond surface slowly rose to within about 6 feet of the crater floor by June 19. On June 20, commercial helicopter pilots reported to us that the lake was actively overturning and had covered much of the floor of the crater. A small spatter cone on the floor of the crater adjacent to the lava lake was actively spattering lava as high as 30 feet above the crater floor. Within a few hours of the start of the episode 51 vents, the lake surface had lowered to about 165 feet below the rim of Pu`u `O`o.

There were several interesting earthquakes during this two-week period. On June 13 at 8:31 a.m., a magnitude 3.5 earthquake occurred about 19 miles below Mauna Kea Volcano. This type of earthquake is caused by bending of the crust below the island in response to the weight of the volcanoes. Between 6:37 p.m. on June 17 and 7:48 a.m. on June 18, a swarm of earthquakes occurred beneath Lo`ihi Seamount. Fourteen had magnitude between 1.0 and 2.0, but none was larger. They ranged from about six to 16 miles deep. This was the first significant earthquake activity beneath Lo`ihi since a much larger, and more intense, swarm occurred last December 19 to 23. The December swarm included more than 400 events, compared to only 61 counted events in this swarm. The recurring earthquake activity beneath Lo`ihi Seamount is a reminder that it is an active Hawaiian volcano, albeit less familiar than the others because it is completely submerged. It is uncertain whether these earthquake swarms indicate eruptions on Lo`ihi, or merely occur in response to magmamovement within and beneath the volcano.