VOLCANO WATCH: Kīlauea’s Ongoing Eruption, A Rising 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.)

It has been an exciting week at Kīlauea Volcano, as the summit eruption that began on the evening of Dec. 20 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.

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 1,060 cubic feet 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 Dec. 26, 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 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 Dec. 25 to 3,800 tons per day on Dec. 30.

The lava lake level has been rising slowly again since Dec. 27 and, as of writing this article, it has reached a new peak elevation of 2.300 feet above sea level and depth of 603 feet. The erupted volume to this point is more than 700 million cubic feet, or about 8,000 Olympic-sized swimming pools. The eruption rate has decreased to approximately 353 cubic feet per second. On Dec. 30, the lake measured 875 yards east-west and 580 yards north-south, covering an area of 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 2,560 feet above sea level, then another 16 feet of rise will have it overflowing the lowermost rim of Halemaʻumaʻu on the northeast side. Since the lava lake is currently at about 2,300 feet avove sea level, it has about 262 feet to rise before it reaches the level of visibility. When it does so depends on the rate of lava being erupted.

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.)

Assuming a constant eruption rate of 353 cubic feet per second, it would take approximately 45 days for lava to fill Halemaʻumaʻu to just over 2,560 feet above sea level, therefore becoming visible from Kīlauea Overlook. Several days later it would start overflowing the lowermost rim of Halemaʻumaʻu at just below 2,625 feet above sea level. 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.

Volcano Activity Updates

Kīlauea Volcano is erupting. Its USGS Volcano Alert level is at WATCH. 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 593 to 608 feet 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, visit Big Island Now or go online.

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 about five miles. The largest recorded earthquake was a M2.2 beneath the volcano’s northwest flank on Dec. 28 at 12:47 a.m. HST. The earthquake activity on Mauna Loa’s northwest flank, which began on Dec. 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, go online.

There were seven events with three or more felt reports in the Hawaiian Islands during the past week:

• An M2.8 earthquake one mile E of Pāhala at a 20-mile depth on Dec. 28 at 1:26 p.m. HST,
• An M2.8 earthquake five milies ENE of Pāhala at a 19-mile depth occurred on Dec. 26 at 5:55 a.m. HST,
• An M2.2 earthquake three miles ENE of Pāhala at a 19-mile depth occurred on Dec. 24 at 7:56 p.m. HST,
• An M1.7 earthquake three miles ENE of Pāhala at a 20-mile depth occurred on Dec. 24 at 7:28 p.m. HST,
• An M3.6 earthquake four miles ENE of Pāhala at a 20-mile depth occurred on Dec. 24 at 7:18 p.m. HST,
• An M3.3 earthquake four miles NE of Pāhala at a 19-mile depth occurred on Dec. 24 at 7:13 p.m. HST.
• An M1.7 earthquake one mile SE of Pāhala at a 20-mile 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. Email questions to [email protected].