Volcano Watch — Kīlauea’s ongoing eruption: a rising lava lake

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It has been an exciting week at Kīlauea Volcano as the summit eruption that began on the evening of December 20th continues. The eruption remains confined within Halemaʻumaʻu crater. Monitoring data show no signs of activity migrating from the summit into the rift zones, nor indications of summit collapse like those in 2018.

Volcano Watch is a weekly article and activity update written by U.S. Geological Survey Hawaiian Volcano Observatory scientists and affiliates.

Color photograph of lava lake

Annotated eruption photograph taken at 5 p.m. HST on December 30, 2020, from the south rim of Halemaʻumaʻu, Kīlauea Volcano summit. USGS photo by K. Lynn. (Public domain.)

The primary hazard from this eruption at this time is vog (volcanic air pollution) produced by the gases emitted at the summit. USGS Hawaiian Volcano Observatory (HVO) scientists continue to closely monitor the eruption. 

As last week’s “Volcano Watch” went to press, lava continued to erupt from two vents on the west and north sides of Halemaʻumaʻu crater at a combined rate of approximately 30 cubic m (1060 cubic ft) per second. The rise of the lava lake was slowing due to the funnel-like shape of Halemaʻumaʻu. 

By Christmas night, the lava lake had risen slightly above the level of the north vent, which to this point was the dominant source of lava for the eruption.  Lava fountaining from the north vent, which built an amphitheater-shaped cone surrounding it, drove circulation in the lava lake apparent in the motion of the crust. 

Early in the morning on December 26th, the biggest change in eruptive activity was observed. At approximately 3 a.m. HST, activity at the west vent increased dramatically as the fountaining at the north vent died out. HVO scientists observing the lake witnessed lava draining back into the north vent and the lake level dropped 5 meters (26 feet) over the next few hours. This left a ‘bathtub ring’ around the edge of the lake, marking the lake’s high point. The change in active vent also saw a decrease in sulfur dioxide (SO2) gas output, down from 16,000–20,000 tonnes per day on December 25th to 3,800 tons per day on December 30th

The lava lake level has been rising slowly again since December 27th and, as of writing this article, it has reached a new peak elevation of 701 m (2300 feet) above sea level (asl) and depth of 184 m (603 feet). The erupted volume to this point is more than 20 million cubic meters (700 million cubic feet) or about 8,000 Olympic-sized swimming pools!  The eruption rate has decreased to approximately 10 cubic m (353 cubic ft) per second. On December 30, the lake measured 800 m (875 yd) east-west and 530 m (580 yd) north-south, covering an area of 33 hectares (82 acres). Lava continues to erupt from the west vent. 

One of the most common questions that HVO gets is, “When will the lake be visible from an open area of Hawai‘i Volcanoes National Park?” and “Will the lava lake fill Halemaʻumaʻu?” These questions are difficult to answer because the activity within Halemaʻumaʻu is dynamic. After the eruption first started, the lava lake rose rapidly both due to the shape of the base of Halemaʻumaʻu (inverted cone) and the initially high rates of lava being erupted.  

Since then, the rate of lava being erupted has varied, especially as activity shifted from the north to the west vent, with associated lava drainback into the inactive north vent and a temporary decrease in lake level. However, HVO has done some preliminary calculations to try and answer these questions using topographic models and the most recent eruption rate.  

The lava lake should be visible from Kīlauea Overlook once it reaches an elevation just over 780 m (2560 ft) asl, then another 5 m (16 ft) of rise will have it overflowing the lowermost rim of Halemaʻumaʻu on the northeast side. Since the lava lake is currently at about 701 m (2300 feet) asl, it has about 80 m (262 ft) to rise before it reaches the level of visibility. When it does so depends on the rate of lava being erupted.  

Assuming a constant eruption rate of 10 cubic m (353 cubic ft) per second, it would take approximately forty-five days for lava to fill Halemaʻumaʻu to just over 780 m (2560 ft) asl, therefore becoming visible from Kīlauea Overlook. Several days later it would start overflowing the lowermost rim of Halemaʻumaʻu at just below 800 m (2625 ft) asl. However, it would likely take longer as the eruption rate has been fluctuating and generally decreasing. If lava did overflow Halema’uma’u, it would then need to fill the extensive down-dropped block area before overflowing onto the main caldera floor.  

HVO continues to closely monitor this eruption in Halemaʻumaʻu at Kīlauea’s summit. Check the HVO website for photo, video, and text updates: www.usgs.gov/hvo. 

Color map of volcano

This map of Halema‘uma‘u at the summit of Kīlauea shows 20 m (66 ft) contour lines (dark gray) that mark locations of equal elevation above sea level (asl). The map shows that the lava lake (approximate area marked in red) has filled 184 m (603 ft) of Halema‘uma‘u since the eruption began at approximately 9:30 p.m. HST on December 20, 2020. USGS map. (Public domain.)

Volcano Activity Updates  

Kīlauea Volcano is erupting. Its USGS Volcano Alert level is at WATCH (https://www.usgs.gov/natural-hazards/volcano-hazards/about-alert-levels). Kīlauea updates are issued daily.   

Activity is confined to Halemaʻumaʻu with lava erupting from vents on the northwest side of the crater. Over the past 24 hours, the lava lake depth measurements have ranged from 181 m to 185 m (593 to 608 ft) deep.  Preliminary analysis of sulfur dioxide emission rates measured Wednesday (Dec. 30) show that the rates are about 3,800 tonnes/day, in the range of values common for the pre-2018 lava lake. Summit tiltmeters recorded neither inflationary nor deflationary tilt over the past two days. Seismicity remained elevated but stable, with steady elevated tremor and a few minor earthquakes. For the most current information on the eruption, see https://www.usgs.gov/volcanoes/kilauea/current-eruption.

Mauna Loa is not erupting and remains at Volcano Alert Level ADVISORY. This alert level does not mean that an eruption is imminent or that progression to eruption from current level of unrest is certain. Mauna Loa updates are issued weekly.    

This past week, about 60 small-magnitude earthquakes were recorded beneath the upper-elevations of Mauna Loa; most of these occurred at depths of less than 8 kilometers (about 5 miles). The largest recorded earthquake was a M2.2 beneath the volcano's northwest flank on December 28 at 12:47 a.m. HST. The earthquake activity on Mauna Loa’s northwest flank, which began on December 4, 2020, has subsided to average long-term trends. Global Positioning System (GPS) measurements recorded contraction across the summit caldera since mid-October with extension (summit inflation) resuming in the past few weeks, consistent with magma supply to the volcano's shallow storage system. Gas concentrations and fumarole temperatures at both the summit and Sulphur Cone on the Southwest Rift Zone remain stable. Webcam views have revealed no changes to the landscape over the past week. For more information on current monitoring of Mauna Loa Volcano, see: https://volcanoes.usgs.gov/volcanoes/mauna_loa/monitoring_summary.html.  

There were 7 events with 3 or more felt reports in the Hawaiian Islands during the past week: a M2.8 earthquake 2 km (1 mi) E of Pāhala at 33 km (20 mi) depth on Dec. 28 at 1:26 p.m. HST, a M2.8 earthquake 9 km (5 mi) ENE of Pāhala at 31 km (19 mi) depth occurred on Dec. 26 at 5:55 a.m. HST, a M2.2 earthquake 6 km (3 mi) ENE of Pāhala at 30 km (19 mi) depth occurred on Dec. 24 at 7:56 p.m. HST, a M1.7 earthquake 6 km (3 mi) ENE of Pāhala at 32 km (20 mi) depth occurred on Dec. 24 at 7:28 p.m. HST, a M3.6 earthquake 7 km (4 mi) ENE of Pāhala at 33 km (20 mi) depth occurred on Dec. 24 at 7:18 p.m. HST, a M3.3 earthquake 8 km (4 mi) NE of Pāhala at 32 km (19 mi) depth occurred on Dec. 24 at 7:13 p.m. HST, and a M1.7 earthquake 2 km (1 mi) SE of Pāhala at 33 km (20 mi) depth occurred on Dec. 24 at 7:12 p.m. HST. 

HVO continues to closely monitor both Kīlauea’s ongoing eruption and Mauna Loa for any signs of increased activity.   

Please visit HVO’s website for past Volcano Watch articles, Kīlauea and Mauna Loa updates, volcano photos, maps, recent earthquake info, and more. Email questions to askHVO@usgs.gov.   

Volcano Watch is a weekly article and activity update written by U.S. Geological Survey Hawaiian Volcano Observatory scientists and affiliates.