Kīlauea’s steady pattern of eruptive activity ended this past week with a dramatic change in activity contained within its summit crater of Halemaʻumaʻu, just 9 days ahead of the eruption’s one-year anniversary. At 3pm on Tuesday, September 20th, several things began to happen at once. The lava level in the active lake began its 33 foot (10 m) drop, joined by most of the rest of the crusted crater floor, which also sagged by several yards (meters). A swarm of over 80 earthquakes began approximately 1 mile (1.5 km) beneath the crusted lake, with 19 events over magnitude 2 and the largest registering at 2.9. Rapid inflation resulting in 12 microradians of ground tilt on the north rim at Uēkahuna began around 4:20pm, with new breakouts of lava emerging from new cracks surrounding the crater floor. The underground changes ceased around 6pm, while the new flows within Halemaʻumaʻu persisted much longer.
There is still no increased lava threat outside of Hawaiʻi Volcanoes National Park, though gas emissions continue to produce vog that impacts downwind communities in south and west Hawaiʻi. According to the USGS, “All activity was restricted to the summit region and there is no indication of activity migrating into either rift zone.”
We review the monitoring signals, webcam time-lapses, images, and reports courtesy of the USGS Hawaiian Volcano Observatory that document this unusual episode of activity, and discuss live viewer questions, while sharing lava viewing highlights and special time-lapses of the sequence. We consider the relation of this event to the recent summit deflation, and whether the signals may actually indicate an intrusion, with comparison to tilt signals from previous events. We cover Maunaloa, whose earthquakes continue to slowly trend upwards even as its summit continues its recent minor changes, as well as American Samoa where seismic activity remains low, but more USGS monitoring data is now available.
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