The June 27th lava flow slows, surges into Pāhoa, then slows again

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Just over a week ago Kīlauea Volcano's June 27th lava flow was barely moving forward, but then it surged into Pāhoa. With that in mind, the USGS Hawaiian Volcano Observatory (HVO) is using this Volcano Watch article to summarize how the lava went from being a somewhat distant threat to an immediate one in just a few days.

In mid-October, following weeks of relatively slow advance—less than 1.6 km (1 mi) in three weeks—the leading edge of the June 27th lava flow stalled. While there were no illusions that it had stopped for good (there were still plenty of lava outbreaks behind the flow front, indicating that it remained active), residents downslope of the lava flow were granted some extra time to prepare for its possible arrival. The threat may even have seemed a bit abstract, with lava still more than 1 km (0.6 mi) upslope of AP‘A‘ā Street/Cemetery Road and almost 2 km (1.2 mi) from Pāhoa Village Road.

The situation began to change on October 13, when a narrow finger of lava broke out from behind the flow front and moved along the southeast margin of the existing flow, at times reaching rates over 150 m (165 yd) per day. On October 22, the narrow finger overtook the stalled flow front and became the leading edge of the flow. The following day it advanced 390 m (430 yd), due in part to a local gully, which narrowed and focused the lava flow.

On Saturday, October 25, at 3:20 a.m., HST, lava reached AP‘A‘ā Street—a milestone with historical, geographical, and psychological implications. The June 27th flow had entered the community of Pāhoa and was impacting human infrastructure.

Pushing closer towards town, lava inundated the Pāhoa cemetery, just 0.8 km (0.5 mi) from Pāhoa Village Road, on the morning of October 26. By that afternoon, the flow was moving through a grassy field and adjacent forest, and burning vegetation resulted in frequent, and often loud, methane blasts. These blasts—common wherever lava encounters vegetation—are a significant, yet underappreciated, hazard to anyone nearby.

As lava moves through vegetated ground, plant materials covered by the flow, including roots, continue to burn. This burning produces methane, which can accumulate beneath the flow and, under certain circumstances, burst through the flow surface or along the flow margins. Occasionally, the methane bursts can be quite large—powerful enough to throw hot rock (and anyone standing on it) into the air.

Moving at 5–10 meters (yards) per hour, with the advance rate varying due to changes in the slope of the land, the lava flow reached a fence line marking private property on the morning of October 28. As it moved through the private land, the lava engulfed everything in its path, including a utility shed, trees in a small macadamia nut orchard, and a pile of tires. The burning tires produced a thick plume of black smoke that was visible for miles, causing both interest and concern among Pāhoa and nearby residents!

Over the subsequent days, the lava flow continued to advance through private property toward Pāhoa Village Road, although the advance rate of the flow front slowed to only a few meters (yards) per hour, and eventually stalled on October 30. Such slowdowns are common in pāhoehoe flows. Breakouts upslope of the flow front can divert supply away from the leading edge, and flow inflation can cause the flow to thicken instead of pushing forward.

Nevertheless, it is important to remain vigilant. Inflated flows can suddenly burst forth, releasing streams of lava that can move rapidly over small distances—behavior that was common in the days prior to the October 30 slowdown. In addition, we expect the flow to continue to widen as upslope breakouts fill in places that were initially bypassed by the leading edge. The process of inflating, surging, and widening is the pattern by which pāhoehoe lava flows grow.

HVO and Hawai‘i County Civil Defense are monitoring the ongoing lava flow activity around the clock to keep abreast of these and other developments. Maps, photos, and detailed updates are posted on the HVO and Civil Defense websites at http://hvo.wr.usgs.gov and http://www.hawaiicounty.gov/active-alerts/.

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Volcano Activity Update

The June 27th lava flow from Pu‘u ‘Ō‘ō remained active on Kīlauea Volcano's East Rift Zone. The flow continued to advance northeast and crossed Cemetery Road/AP‘A‘ā Street on October 25. Over the next several days the flow covered a portion of a cemetery and moved through several private lots. By noon on Thursday, October 30, the flow front had stalled and was 150 m (164 yd) from Pāhoa Village Road. Within the Pu‘u ‘Ō‘ō crater, glow was visible above several small outgassing openings in the crater floor.

The summit lava lake within Halema‘uma‘u Crater produced nighttime glow that was visible via HVO's webcam over the past week. The lava level was relatively steady over much of the past week, and was roughly 60 m (200 ft) below the rim of the Overlook crater. Deflation starting Oct 29 was associated with a minor drop in lava level, which continues at the time of writing (Thurs., Oct. 30).

There were no earthquakes reported felt on the Island of Hawai‘i during the past week.