Volcano Watch — Pu`u `O`o eruption is volcano's 50th episode

On Monday, Feb. 17, at about 7:30 p.m., lava began erupting from a fissure on the southwest flank of Pu`u `O`o. The event was immediately noticeable in the Glenwood area by the strong glow from the rift zone; it was also marked by deflation of Kīlauea's summit recorded by tiltmeters and by increased tremor recorded by a seismometer near Pu`u `O`o. As of Friday, the 500-foot-long fissure was still active, producing low lava fountains, less than 15 feet high, and spatter.

The main lava flow from the fissure initially advanced to the north and northwest, covering an older flat-lying pahoehoe flow that was erupted in July 1986 from a fissure in the same area. Since the first day of this event, the flow has advanced very little, extending no farther than 0.75 miles from the fissure.

The flow has formed a pond 12-20 feet deep that is contained within levees that developed as the margins of the flow cooled and hardened. The levees build progressively higher as they are repeatedly coated by small overflows from the rising pond. This is the 50th eruptive episode in the Pu`u `O`o-Kupaianaha eruption series, which began in January 1983.

The lava pond within the Pu`u `O`o Crater drained approximately 130 feet as the fissure eruption began, to a depth of 250 feet below the crater rim. This puts the elevation of the pond only slightly higher than the elevation of the erupting fissure.

The outbreak of the fissure eruption uprift of Kupaianaha was not unexpected. Once the Kupaianaha vent shut off, magma pressure beneath Pu`u `O`o increased, leading to a rupture in the side of the cone.

The Kupaianaha vent is still inactive. The last active flows from the Kuipaianaha lava tube were spotted on February 6.

There were no earthquakes greater than magnitude 3 on the Big Island this week.