Volcano Watch — Eruption pauses; earthquake shakes isle

The eruption at the episode 51 vent slowed dramatically on Thursday at about 2:00 p.m. and by Friday morning there was no eruptive activity at the vent on the west flank of the Pu`u `O`o cone. The activity in the pond inside the Pu`u `O`o cone suggests that the current lull in activity is just another pause in episode 51.

From March 7 through March 17, the eruption was marked by a series of starts and stops. The following is a summary of the events since March 7, when episode 51 began at about 12:45 in the afternoon. By 9:00 p.m. the vent had stopped, but by midnight, activity had resumed. This period of activity continued until March 12, when the volume of erupting lava began to sharply decrease at about 2:30 in the afternoon. By 9:00 that evening, the vent had become inactive. 

On March 14, the vent again became active, starting about 11:30 in the morning and continuing until about 6:00 p.m. the next day. On March 17 at about 6:00 a.m., the vent abruptly restarted and continued until about 3:00 a.m on March 18, when the activity apparently stopped briefly. By 6:00 a.m. that same day, the vent was again active, but with only a small-volume eruption. The level of activity increased until about 1:30 in the afternoon, but the volume remained at perhaps half that of the previous eruptive intervals. 

Activity was continuous, starting at 1:30 p.m. on the 18th, until about 2:00 p.m on March 26, when the level of ground shaking near the vent dropped to noise levels. During this period of continuous activity, the volume of lava erupted fluctuated sharply, with periods of intense activity interspersed with periods of lower activity. Before the vent stopped erupting on Thursday, the activity had been vigorous for about two days.

The flows from the repeated eruptive periods in episode 51 have not progressed far from the vent, as seen in the figure. However, flows did reach the forest to the northwest of the vent on Thursday afternoon and also approached within about 50 feet of one of our field instruments, which we removed to a safer site. Episode 51 is now quiet. If subsequent eruptive or intrusive activity begins in a different location, then episode 51 will be over. Such activity would be accompanied by a fairly sharp drop in the level of summit tilt as magma migrates from beneath the summit to the new eruptive or intrusive site. We presently think it most likely that activity will simply start again at the same vent and that episode 51 will continue.

At 6:32 a.m. Friday morning, many island residents were awakened by a sharp earthquake with a magnitude of 4.1 located roughly 7 miles deep and 12 miles north of Pahala. The fault that slipped is apparently nearly vertical and oriented northeast-southwest, parallel to the slope of the volcano. This earthquake occurred in an area of recurrent seismicity and is apparently related to seaward sliding of the south flank of Mauna Loa Volcano, rather than being directly caused by magma movement inside Mauna Loa Volcano. 

This past week, Hilo played host to a group of international scientists who attended a conference at the University of Hawai`i at Hilo campus on climate, volcanism, and global change. The main topic of the conference was the role that volcanic gas emissions play in changing climate on a global scale.