Active surface flows on the northeast flank of Pu‘u ‘Ō‘ō on March 12, 2015. The activity is a continuation of a breakout that began on February 21, which diverted lava from the tube system and helped to starve the supply of lava to the June 27th flow front near Pāhoa. This breakout on Kīlauea is still active and has now reached 2.5 km (1.6 mi) northeast of Pu‘u ‘Ō‘ō, but does not pose an immediate hazard to any community. USGS photo.

(Volcano Watch is a weekly article written by scientists at the U.S. Geological Survey’s Hawaiian Volcano Observatory.)

Lava erupting from Pu‘u ‘Ō‘ō since mid-March 2015 has spread slowly and irregularly across three areas located within about 7 km (4 mi) from the vent on Kīlauea Volcano’s East Rift Zone. These active lava flows are not presently posing an immediate threat to any community in the Puna District of the Island of Hawai‘i.

The currently active flows are reminiscent of the slow-moving Kahauale‘a flows that were active in 2013–2014, before the new vent opened on the north flank of Pu‘u ‘Ō‘ō on June 27, 2014, and sent flows toward Pāhoa. The Kahauale‘a flows spread gradually north and northeast from Pu‘u ‘Ō‘ō in fits and starts, intermittently advancing a short distance before stopping as the supply of lava changed.

The current activity is a welcome relief from the long, tube-fed June 27th lava flow that spread 22 km (14 miles) eastward from Pu‘u ‘Ō‘ō and repeatedly threatened the Pāhoa area. That flow entered Pāhoa in late October 2014, nearly cutting the Pāhoa Village Road, before becoming inactive in mid-November.

Days later, a new breakout upslope developed into a second flow lobe that reached to within 500 m (550 yd) of the Pāhoa Marketplace just before Christmas. This lobe stopped advancing, but continued to spread laterally just upslope from the Marketplace over the next few months. Because these breakouts, and others farther upslope, were widely dispersed, no single flow lobe became focused, which limited the advance of the flow front.

Lava was further diverted from the June 27th flow front on February 21, when a series of flows broke out of the lava tube near its source on the north flank of Pu‘u ‘Ō‘ō. This breakout was followed by another large breakout on March 9 near Puʻu Kahaualeʻa—an old, nearly buried cone about 2 km (1.2 mi) northeast of Pu‘u ‘Ō‘ō. Together, these two breakouts captured the entire supply of lava from the tube, effectively starving the June 27th flow front, and, by March 13, surface flows near the Pāhoa Marketplace were no longer active.

Even as the flows near Pāhoa were dying out, lava slowly reoccupied the tube below Puʻu Kahaualeʻa. This culminated in a third area of breakouts about 6 km (4 mi) northeast of Pu‘u ‘Ō‘ō. Lava has not reoccupied the tube below this breakout.

All three of these breakouts remained active this past week. The USGS Hawaiian Volcano Observatory (HVO) is currently monitoring the breakouts with bi-weekly overflights, after which maps and photos of the activity are posted on the HVO website (http://hvo.wr.usgs.gov/). HVO scientists are also using other methods to track the status of Kīlauea’s ongoing eruption, including Webcam images, satellite imagery, sulfur dioxide gas emission measurements, and continuous recording of earthquake and ground deformation by instruments on the volcano.

The lava flows of the past 8 months have demonstrated the complex factors that affect the ways in which lava moves across the ground. The intertwining conditions that enabled lava to advance right to Pāhoa’s doorstep were remarkable. For example, older lava flows and large ground cracks along the East Rift Zone kept the June 27th flow narrow, facilitating its advance and promoting development of a robust lava tube system.

The constant uncertainties in estimating if the June 27th lava flow would continue moving downslope, what path it would take, how fast it would advance, and whether lava would cover Pāhoa Village Road, Pāhoa Marketplace, Highway 130, and other vital infrastructure, has made this a somewhat harrowing experience. With lava flow advance rates varying from a few meters (yards) to more than 500 m (550 yards) per day, flow forecasts were imperfect at best.

Fortunately, the June 27th flow stopped before completing what seemed to be a certain path to significant destruction in Pāhoa.

The Puna District can breathe more freely for the moment, but the activity over the past 8 months has demonstrated that the area is not immune to Kīlauea’s lava flows. While the currently active flows do not represent an immediate hazard to communities, they could eventually. We must all remember that unpredictable changes at Pu‘u ‘Ō‘ō can quickly change the hazard prognosis.

http://youtu.be/zeoe6X45Y_A
Time-lapse movie of Pu’u ‘O’o Crater North Flank from the North Rim. April 9-16, 2015. Images courtesy of USGS/HVO