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

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 26^th, 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 25^th to 3,800 tons per day on December 30^th.

The lava lake level has been rising slowly again since December 27^th 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. 

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.)