When will Halemaʻumaʻu fill with lava? — USGS Volcano Watch

USGS Hawaiian Volcano Observatory (HVO) staff are often asked, “Will lava erupted during the ongoing Kīlauea summit eruption in Halemaʻumaʻu eventually flow out of the caldera? And if so, when?” The answer is complicated...

The topography of Kaluapele, Kīlauea volcano’s summit caldera, is stepped—a series of ledges at different elevations. The deepest part, which has been covered with lava flows during the ongoing episodic eruption in Halemaʻumaʻu that began in December 2024, collapsed downwards in 2018.

The volume of the void left within the caldera by the 2018 collapse was approximately 0.20 cubic miles (825 million cubic meters) and the bottom of Halemaʻumaʻu crater settled at an elevation of 1,696 feet (517 meters) above sea level. This means that the base of Halemaʻumaʻu after the 2018 collapse was 2,395 feet (730 meters) lower than Uēkahuna bluff—the highest point on Kīlauea at an elevation of 4,091 feet (1,247 meters).

Sources/Usage: Public Domain.

This aerial photograph shows the volcanic vent complex in Halema‘uma‘u on July 16, 2026, following Kīlauea summit eruption episode 51 the day before. Nearly the entire western portion of the crater floor was resurfaced with lava flows, while areas that are brown colored on the left side of the photograph were draped in tephra fallout from the lava fountaining. The vent complex remains 215 feet (65 meters) below the crater rim. USGS photo by E. Johnson.

Five eruptions within Halemaʻumaʻu between 2020 and 2023 filled in about 25% of the 2018 collapse volume, raising the crater floor by 1,313 feet (400 meters) to an elevation of 3,009 feet (917 meters).

An additional 35% of the 2018 collapsed volume has been filled in by the ongoing episodic fountaining eruption in Halemaʻumaʻu over the past year and a half, and the crater floor is an additional 295 feet (90 meters) higher. Although the ongoing eruption has filled in more volume than the previous five eruptions, it has filled in less depth because the area that collapsed in 2018 was cone shaped. So, the deepest part filled the fastest during the first five eruptions after 2018 and required less volume of lava to do so. Lava flows during the ongoing eruption have covered a much larger area (1,116 acres or 452 hectares) and therefore accrue thickness more slowly.

In total, 60% of the 2018 collapsed volume has been filled in, raising the crater floor by 1,608 feet (490 meters). Assuming that the ongoing Kīlauea summit eruption continues at the same rate is has over the past year (0.04 cubic miles or 183 million cubic meters) for the next year and a half, the 2018 collapse could be almost totally filled in by early 2028.

Once the 2018 collapsed area fills in, lava will flow onto the east part of the main caldera floor. The last time lava flowed here was over 50 years ago, when a series of fissures on the south caldera rim and floor opened in July 1974, erupting lava flows that covered the southern portion of the caldera floor.

Once lava flows onto the caldera floor, it has a much bigger area to cover: over 2,500 acres (1,000 hectares), so it will take even longer to accrue thickness. The volume required to fill the main caldera is difficult to calculate because it is topographically “breached” to the southwest, meaning lava flows will spill out this way before reaching the taller rim on the north side. But since effusive volcanoes always deposit more lava closer to its sources, they build up shields that eventually overcome the local topography. In any case, at least another 0.22 cubic miles (910 million cubic meters) is required to fill the caldera, which at current rates would take an additional five years.

Also remember, as the lava fountaining episodes at the summit of Kilauea have demonstrated, eruption rates vary over time. Some of the lava fountaining episodes have erupted more lava than others, particularly the episodes during which both the north and south vent produce fountains. Other episodes, with only one vent erupting a lava fountain at a lower height, produce less lava. This variability makes all of our filling forecasts very rough estimates.

Sources/Usage: Public Domain.

This map shows thickness values for lava flows within Halema‘uma‘u crater from the Kīlauea summit eruption that began on December 23, 2024. These values were calculated by topographic differencing between a digital elevation model collected on June 30, 2026—after eruptive episode 50—and one from before the eruption began. Also included here are west-to-east profiles across the summit caldera, depicting topographic changes since 2018. Profiles are provided for the periods before the 2018 caldera collapse, shortly after the 2018 collapse, following each of the five summit eruptions from 2020–2023, and for this eruption following the end of episode 50. Also shown is the maximum depth of the 2019–2020 Halema‘uma‘u water lake.

Another important factor to consider is the elevation of the vents within Halemaʻumaʻu, which remain 215 feet (65 meters) lower than the crater rim. If the vents grow above the crater rim, this may also send lava downslope to the southwest within Hawai'i Volcanoes National Park where it would pose no threat to communities. Lava will always flow in the downslope direction, but since the emplacement of flows will continue to change the vent geometry and local topography, they could also remain within the caldera.

The easiest answer to the question of whether lava will flow out of the caldera is, it depends! It depends on how long this eruption continues, what rate lava erupts over time, and where it builds up the area around the vents. While there is currently no sign of this eruption changing, it also depends on whether eruptive activity at Kīlauea changes, as a new eruption beginning elsewhere is always a possibility.

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