The past few weeks have been exciting for volcano watchers on Hawaii Island, especially for visitors to Hawaii Volcanoes National Park’s Jaggar Museum overlook, where views of the active summit lava lake within Halema‘uma‘u have been spectacular.
Since April 21, high lava lake levels in the informally named “Overlook crater” within Halema‘uma‘u at the summit of Kilauea Volcano have produced multiple overflows of pahoehoe lava onto the floor of Halema‘uma‘u. As of April 26, these new flows have covered just under 90 acres or nearly three-fourths of the Halema‘uma‘u crater floor. They are the first significant overflows of the summit lava lake since April-May 2015.
Meanwhile, on Kilauea’s East Rift Zone, the Pu‘u ‘O‘o cone has been inflating and expanding steadily since mid-March, with the west pit lava pond level rising, the main crater floor uplifting and cracking, and small lava flows intermittently active inside the crater. The USGS Hawaiian Volcano Observatory released a Volcano Activity Notice on April 17 to highlight this activity and to note that the past two similar changes resulted in new breakouts of lava from new vents on the Pu‘u ‘O‘o cone.
So, what is going on with Kilauea?
In a nutshell, the magmatic plumbing system extending from the summit reservoir to Pu‘u ‘O‘o is pressurizing. This means that an excess of magma is being stored in the system, causing swelling (inflation and expansion measured by tiltmeters and GPS), an uptick in microearthquakes as the surrounding rocks are stressed, and an increase in the height of lava lakes at both the summit and Pu‘u ‘O‘o.
What’s causing this pressurization? This is where things get less certain.
Two general possibilities are being discussed by HVO scientists. It could be due to a pulse of increased magma supply to the system from the deeper summit reservoir (and ultimately the mantle source). Perhaps more likely, it could be that one or more obstructions have developed somewhere in the system between the summit, Pu‘u ‘O‘o, and the episode 61g vent, and are now backing things up. A combination of both factors is also possible.
Arguments against increased supply from depth: We have seen no increases in gas emissions, tephra production, or lava temperature that might be expected with a magma surge, although we are still collecting data to verify these observations. Deformation data initially showed very little change in the shallow summit magma reservoir when Pu‘u O‘o began inflating in mid-March. An influx of new magma would have been expected to affect the summit first.
Perhaps the favored hypothesis at present is that a breakdown of the connection between the Pu‘u ‘O‘o reservoir and the episode 61g vent has caused a backup from Pu‘u ‘O‘o uprift to the summit magma reservoir and lava lake.
Why this blockage developed is another question. Did the effusion rate from Pu‘u ‘O‘o slow to the point where efficient drainage out the 61g vent could not be sustained, essentially causing magma to back up into the Pu‘u ‘O‘o reservoir and cone? This is a difficult question to answer, but there is ample evidence that the summit reservoir does respond to changes at the Pu‘u ‘O‘o vent. Impeding outflow of magma from the summit to the 61g flow field could be the reason the lava lake within Halema‘uma‘u is rising.
What is next for Kilauea?
As long as the system remains pressurized, we expect continued high levels of the summit lava lake and Pu‘u ‘O‘o lava pond, overflows onto the floor of Halema‘uma‘u, and ongoing deformation and microearthquakes.
This activity could end with a new breakout at Pu‘u ‘O‘o relieving pressure on the entire system and lowering the lava level at both locations. Alternatively, magma could find an another pathway to relieve the pressure, such as an intrusion into the south caldera (as occurred in 2015), Southwest Rift Zone, or uprift of Pu‘u ‘O‘o along the East Rift Zone
HVO is carefully watching various data streams to catch early signs of change that might indicate Kilauea’s next move. Like many of you, we, too, are marveling at the sight of lava on the floor of Halema‘uma‘u.
Volcano Activity Updates
This past week, Kilauea Volcano’s summit lava lake level fluctuated with summit inflation and deflation, eventually rising high enough to overflow onto the floor of Halema‘uma‘u multiple times beginning April 21. On the East Rift Zone, the 61g lava flow remained active with breakouts on the upper part of the flow field. There were no active lava flows on the pali, coastal plain, or entering the ocean. The 61g flows do not pose an immediate threat to nearby communities.
Mauna Loa is not erupting. Rates of deformation and seismicity have not changed significantly over the past week. Few small-magnitude earthquakes occurred beneath the summit and upper flanks of the volcano, primarily at depths shallower than 5 km (3 mi). GPS and InSAR measurements indicate slowing deformation related to inflation of a magma reservoir beneath the summit and upper Southwest Rift Zone.
Two earthquakes with three or more felt reports occurred in Hawaii this past week: a magnitude-2.7 earthquake 3 km (2 mi) northwest of Keokea at 28.0 km (17.4 mi) depth April 21 at 3:34 p.m. and a magnitude-3.2 earthquake 5 km (3 mi) south of Volcano at 1.8 km (1.1mi) depth inside Hawaii Volcanoes National Park on April 26 at 1:08 p.m.
Please visit HVO’s website (https://volcanoes.usgs.gov/hvo) for past Volcano Watch articles, Kilauea daily eruption updates, Mauna Loa weekly updates, volcano photos, maps, recent earthquake info, and more. Call for summary updates at 967-8862 (Kilauea) or 967-8866 (Mauna Loa). Email questions to askHVO@usgs.gov.
Volcano Watch (https://volcanoes.usgs.gov/hvo/hvo_volcano_watch.html) is a weekly article and activity update written by U.S. Geological Survey Hawaiian Volcano Observatory scientists and affiliates.