Volcano Watch — Eruption episode remains unpredictable

The episode 51 vents on the west flank of Pu`u `O`o, which stopped erupting on May 22, began erupting again on Wednesday morning sometime shortly before dawn. This eruptive interval was extremely vigorous on Wednesday and Thursday, but stopped Thursday during the night. During this interval, the perched pond atop the new shield just uprift from Pu`u `O`o overflowed and fed flows to the north, northwest, west, southwest, and southeast, with the main channelized flow heading to the south. The flows have still not extended beyond previous flows from episode 51, except where they have covered some of the south slope of the Pu`u `O`o cone. As in all previous eruptive intervals in episode 51, the effusion of lava was quiescent, with only low spattering at the vent.

The high eruptive rates during this interval coincided with fairly sharp deflation of the summit as magma stored beneath the summit migrated out the rift zone at rates exceeding those at which new magma was supplied to the summit from deeper beneath Kīlauea. As this eruptive interval ended between about 8:00 p.m. and midnight, the tremor associated with magma movement through the vent dropped sharply, and the summit deflation stopped. As of Friday morning, the summit had not yet begun to reinflate. The episode 50 and 51 eruptions, whose vents are adjacent to one another, have now produced a new lava shield about 170 feet high located on the west side of the Pu`u `O`o spatter/cinder cone.

The episode 50 vents were active in the same area as the episode 51 vents from February 17 until March 3, when episode 50 ended as magma intruded into the upper east rift zone near Pauahi Crater. The episode 51 vents have now been sporadically active since March 7, with nine eruptive intervals. The longest eruptive intervals were from March 31 to April 19 (487.5 hours) and from May 4 to May 22 (434 hours). The longest pause was from April 28 to May 4 (144.5 hours). The shortest eruptive interval was about 8.5 hours and occurred on the first day of episode 51 on March 7. The shortest pause was three hours long and occurred twice, on March 7 and again on March 18. The figure this week shows these eruptive intervals and pauses during episode 51 superposed on the trace of the summit tilt. 

Inflation indicates that the ground surface actually rises as additional magma is stored inside the volcano, whereas deflation indicates that the ground surface subsides as magma in excess of that resupplied from below is erupted or stored in the rift zone, or that the size of the magma storage region inside the volcano expands. There are no clear correlations between the summit tilt changes and when the eruptive intervals start and stop. Therefore, we have been unable to forecast when the episode 51 vents will be active or when they will stop erupting. We expect this sporadic activity at the episode 51 vents to continue with periods of active eruption and extrusion of lava punctuated by pauses.

The shield, and the eruption when the vents are active, can be seen from the overlook on Pu`u Huluhulu adjacent to the Mauna Ulu shield on the Napau Trail in Hawai`i Volcanoes National Park. At night, the glow from Pu`u `O`o and from the vent 51 eruption, when it is active, can be seen from Highway 11 near the Hirano Store in Glenwood.

There were no earthquakes this past week larger than magnitude 3.0. However, a week ago Friday, two occurred, but were not reported in last week's column. The first, which occurred at 4:11 a.m. on May 22, was magnitude 3.2 and was located about 5.4 miles beneath the south flank of Kīlauea. This earthquake was felt in Orchidland and in Honomu. The second, which occurred at 10:30 p.m. the same day, was magnitude 3.0 and was also located about 5.1 miles beneath the south flank of Kīlauea. These earthquakes were caused by seaward sliding of the south flank of Kīlauea Volcano.