Kīlauea summit eruptions outside of Halemaʻumaʻu — USGS Volcano Watch

We are used to seeing eruptions from the summit region of Kīlauea contained to the region that is referred to as Halemaʻumaʻu. Halemaʻumaʻu, home of Pele, is a crater situated within the larger, steep-walled caldera at the summit of Kīlauea named Kaluapele. While eruptions at the summit of Kīlauea most frequently occur within Halemaʻumaʻu, they can occur outside of the modern caldera as well.

Photos of the fissure and lava cascading over the caldera rim from the August 14, 1971, eruption (top left), the extensive fissure system from the July 19–22, 1974 eruption (top center), and an aerial photo of the lava flow field from the September 25, 1982, eruption (top right). The bottom left is an aerial photo of the Keanakākoʻi area following the July 19–22, 1974, eruption with the fissures for the 1971 and 1974 eruptions labeled. The bottom right photo was taken on April 23, 2026, (immediately following the end of episode 45 lava fountaining) and has the August 1971, July 1974, and September 1982 fissures annotated. The red star in the top right, bottom left, and bottom right photos denote the location of the Keanakākoʻi overlook.

Kīlauea summit eruptions in the past several decades have been confined to Halemaʻumaʻu. Starting in 2008 a decade-long lava lake formed within Halemaʻumaʻu that drained during the 2018 caldera collapse. This was replaced for a year and a half by a water lake, which in turn was destroyed during the December 2020 eruption, and since then there have been multiple Halemaʻumaʻu eruptions of which the ongoing lava fountaining just reached episode 45 on April 23, 2026. But further back in time, many eruptions at Kīlauea’s summit occurred outside of Halemaʻumaʻu.

The earliest written documentation of summit eruptions outside of the caldera occurred in 1832 and 1868, both of which were to the east of Kaluapele. The best documented and observed summit eruption to not occur within Halemaʻumaʻu is the episodic lava fountaining eruption in 1959 at Kīlauea Iki that formed Puʻupuaʻi—the prominent cone visible from the Devastation Trail. This eruption occurred to the east of the Kaluapele boundary, and was the subject of a “Volcano Watch” on January 8, 2026.

Eruptions in August 1971, July 1974, and September 1982 occurred south of the caldera rim. In fact, for those that are familiar with the Keanakākoʻi overlook that provides spectacular viewing of the ongoing episodic lava fountaining events, spatter and lava that erupted from the fissure systems for the August 1971 and July 1974 eruptions are right at this location. Hawaiʻi Volcanoes National Park has interpretative signs here that date back to when Crater Rim Drive in this area was still open to motorists.

The August 14, 1971, eruption near Keanakākoʻi lasted for around 10 hours and its lava flow cascaded over the caldera rim and flowed to below Volcano House. The July 19–22, 1974, eruption lava flows also cascaded over the caldera rim before solidifying below Volcano House. However, a lobe of this lava flow also cascaded into the bottom of Keanakākoʻi Crater and continued to flow farther south and east before the eruption ceased. The September 25, 1982, eruption lasted for about 15 hours. This eruption’s fissure system is located in the south caldera region about a mile (approximately 1.6 kilometers) from the Keanakākoʻi overlook within a part of the national park that is closed as a result of the high volcanic hazard. Its associated lava flow reaches to within 700 yards (approximately 630 meters) of the Keanakākoʻi overlook, but is also within the closed, high hazard part of the national park; this lava flow also cascaded over the caldera rim.

Each of the fissure systems that fed these eruptions spanned hundreds of yards (hundreds of meters), with the lava fountains themselves remaining relatively low. Portions of both fissures from the August 1971 and July 1974 eruptions were lowered along with the caldera floor during the collapse that occurred in 2018. Despite subsiding, these fissures remained relatively intact. However, the recent lava fountaining episodes that started on December 23, 2024, have continued to generate lava flows that cover this area intermittently. This has resulted in new lava flows completely covering the August 1971 fissure and portions of the July 1974 fissure on the crater floor.

The remaining parts of the August 1971 and July 1974 fissures and their associated lava flows are visible around the Keanakākoʻi viewing area with interpretative signs along the trail on the side of the road opposite of Keanakākoʻi Crater.

These eruptions outside of Halemaʻumaʻu in the past are evidence that such eruptions could also occur in the future. Most eruptions in new locations are preceded by an increase in shallow seismicity related to magma movement. While not analogous to the precursory seismic activity from the 1970s and 1980s, there has been recent shallow earthquake activity and ground deformation along the south rim of Halemaʻumaʻu—highlighted in a “Volcano Watch” on April 23, 2026.

The ongoing earthquakes beneath Kīlauea’s summit are not currently indicative of an imminent eruption along the south rim of Halemaʻumaʻu, but they are a reminder that the area is dynamic and can experience a variety of volcanic hazards. The USGS Hawaiian Volcano Observatory will continue to closely monitor Kīlauea—a very active volcano where changes can occur quickly across the summit region and beyond.

—

Volcano Watch is a weekly article and activity update written by U.S. Geological Survey Hawaiian Volcano Observatory scientists and affiliates. This week’s article is by HVO geologist Drew Downs.