Kīlauea

• 1. Introduction

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  In 1840, a fissure opened along 35 km of Kīlauea's eastern rift zone, and the glow was so fierce that a person in Hilo, 30 km away, could reportedly read a newspaper at night. That eruption ran for 26 days and released an estimated 205 to 265 million cubic meters of lava. Kīlauea is an active shield volcano on the southeastern shore of Hawaii Island, and that night was far from unusual. Between 1823 and 2024 it erupted 61 separate times, which places it among the most active volcanoes on Earth. Its newest eruption began in December 2024 and was still throwing up lava fountains in 2026.

  Yet for generations, scholars could not agree that Kīlauea was a volcano in its own right. It barely rises above the landscape around it. Why did observers take it for an appendage of a much larger neighbor? How did a chant about a quarrel between two sisters help scientists reconstruct what the mountain did centuries ago? And what happens to the towns, the laboratory and the national park built on a mountain that rarely stays quiet?

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• 2. Pele's Mountain

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  Kīlauea is a Hawaiian word meaning "spewing" or "much spreading", and in Hawaiian tradition the summit pit crater Halemaʻumaʻu is the body and home of Pele. Pele is the goddess of fire, lightning, wind and volcanoes. The crater's name, "House of the amaumau fern", comes from a struggle between Pele and the rain god Kamapuaʻa. Hard pressed by her power to make lava spout from the ground at will, Kamapuaʻa covered her favorite residence with fern fronds. Trapped smoke choked Pele and drove her out. Each god had now shown the other could bring destruction, so the other gods called a draw and divided the island. Kamapuaʻa received the moist windward northeast, and Pele took the drier Kona side. The rusty, singed look of young amaumau fronds is said to be a souvenir of that fight.

  Another chant concerns Hiʻiaka, Pele's sister, who was sent to fetch Lohiau, an attractive man Pele had met on Kauaʻi. Pele set a condition. If Hiʻiaka returned within 40 days, Pele would protect the forests of Puna. The journey took longer, so Pele set the forest on fire. Hiʻiaka came back with Lohiau, found the smoking ruin, and answered in fury by taking Lohiau as a lover before Pele's eyes. Pele killed him and threw him into a pit at the summit of Kīlauea. Hiʻiaka began digging ferociously to recover his body, and rocks flew in every direction.

  Volcanologists now read this story as a record of the Ailāʻau flow, an effusive outpouring that began around 1410 and lasted about 60 years. It covered most of Kīlauea north of the eastern rift zone, in what became the Puna District. Around 1470-1510 the summit collapsed, which the chants appear to describe. Radiocarbon and paleomagnetic dating confirmed the picture. The tradition also corrected a belief. Using the oral history of the Ailāʻau eruption, researchers learned that Kīlauea was far more explosive than they had thought, and the tradition predicts a long period of explosive eruptions. Chants also hinted that surface water once stood at the summit. Oral history can help assess eruption hazards and guide the rehabilitation of affected communities.

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• 3. Built Over a Hotspot

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  Seventy million years of drifting by the Pacific plate over a hotspot in the mantle have produced the 6000 km Hawaiian-Emperor seamount chain, and Kīlauea is its current eruptive center. The prevailing view is that the hotspot has stayed largely stationary through the Cenozoic Era. The nature of hotspots themselves, however, remains uncertain. Kīlauea is one of five volcanoes that make up Hawaii Island. Kohala, the oldest, is more than a million years old and was active for almost 900,000 years before going extinct. Kīlauea is the second youngest in the whole chain. Only Kamaʻehuakanaloa, formerly called Lōʻihi, is younger, and it has yet to break the surface of the sea.

  Kīlauea began as a submarine volcano, growing through underwater eruptions of alkali basalt. It emerged from the ocean with a series of explosive eruptions about 50,000 to 100,000 years ago. Today much of its bulk lies underwater. The part above the sea is a gently sloping shield of about 1500 km2, which is 13.7 percent of the island's surface. Nine-tenths of that surface was laid down in the last 1,100 years.

  At the summit sits a caldera named Kaluapele, "the pit of Pele", measuring 4 by 3.2 km with walls up to 120 m high. Lava flows have breached its southwestern side. Inside it, Halemaʻumaʻu is about 920 m across and 85 m deep, though its shape has changed widely over time. From the caldera, two rift zones run outward. The eastern one stretches 125 km and is covered almost entirely by lava from the last 400 years. Its submerged part reaches a depth of more than 5000 m. The southwestern one is 35 km long and lacks the pit craters and sharp ridge of its eastern counterpart.

  Tectonic extension along these rifts is making the volcano's southern flank slide toward the sea at about 6 to 10 cm per year. The sliding is centered on a fault 7 to 9 km below the surface.

  Kīlauea's identity was long disputed because it appears only as a bulge on the southeastern flank of Mauna Loa. Native Hawaiians and early geologists treated it as an active satellite of its host. James Dwight Dana, who visited the summit in 1840 and studied the islands' volcanoes for decades, called it a flank vent of Mauna Loa. Geologist C. E. Dutton built on Dana's research during an 1884 expedition, and his work led scientists to accept Kīlauea as a separate volcano. Later lava analysis showed that the two have separate magma chambers.

  Still, the neighbors keep time together in odd ways. When Kīlauea lay dormant from 1934 to 1952, Mauna Loa became active. When Mauna Loa stayed quiet from 1952 to 1974, the reverse held. The pattern is not a rule. A Mauna Loa eruption in 1984 began during a Kīlauea eruption and had no discernible effect on it. In 2002, Kīlauea had a high-volume effusive episode just as Mauna Loa began inflating. Geologists suggested that pulses of magma entering Mauna Loa's deeper system may have raised pressure inside Kīlauea. On the 27th of November 2022, Mauna Loa began erupting during Kīlauea's ongoing eruption, the first time since 1984 that both were active at once.

  On Kīlauea's southern flank, the Hilina fault system slips vertically an average of 2 to 20 mm each year. Nobody yet knows whether it is a shallow fault or one that reaches deep into the volcano.

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• 4. Centuries of Fire

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  Around 1510, Kīlauea began a stretch of explosive eruptions that lasted roughly 300 years, until 1790. Scientists found it through radiocarbon dating of the Keanakākoʻi Tephra, named for the cave where adzes were made. That layer formed when lava burst hundreds of meters into the sky and spread ash across the surrounding land.

  The end of that era came with a phreatomagmatic explosion in 1790 that killed more than 400 people, the deadliest volcanic eruption in what became the United States. Among the dead was a party of warriors from the army of Keōua Kuahuula, the last Hawaii island chief to resist Kamehameha I. Their footprints are preserved in what is now Hawaiʻi Volcanoes National Park, and the site is on the National Register of Historic Places. The eruption earned a Volcanic Explosivity Index rating of 4, the highest the Global Volcanism Program gave to any Kīlauea eruption of the last 11,700 years.

  Written records begin around 1820. An English missionary, William Ellis, spent more than two weeks trekking across the volcano in 1823 and produced the first written account of it. Activity around Kaluapele was nearly continuous through much of the 19th century. By 1840, about 3 km3 of lava had been released into the caldera, and the following eight decades produced roughly half that volume.

  In May 1924, Halemaʻumaʻu drained and then sank to nearly 210 m beneath a thick cloud of ash. Explosions began on the 10th of May. They hurled rock chunks of up to 45 kg a distance of 60 m, and smaller fragments of about 9 kg as far as 270 m. On the 18th of May, an enormous blast caused the eruption's only fatality. Columns of ash and gas rose above 9 km, and the eruption was over by the 28th. Activity at the summit faded entirely after 1934.

  Then came silence, until 1952, when a lava fountain 245 m high shot up at Halemaʻumaʻu and the eruption went on for 136 days. In 1960, fissures and earthquakes gave way to a massive aʻā flow that overran evacuated communities and resorts.

  The marathon of the era was Mauna Ulu, which erupted from the 24th of May 1969 to the 24th of July 1974. It began as a fissure between two pit craters, Āloi and Alae, and built a new shield. Fountains reached as high as 540 m, and both pāhoehoe and aʻā lava poured out. The eruption added 230 acres to the island and was then the longest flank eruption recorded on any Hawaiian volcano. In early 1973, an earthquake briefly moved the eruption to the craters Pauahi and Hiʻiaka. A magnitude 7.2 earthquake later partly collapsed the summit, and the volcano then paused until 1977.

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• 5. Thirty-Five Years of Lava

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  On the 3rd of January 1983, a vent on the eastern rift zone began to fountain, and the lava quickly built the cone called Puʻu ʻŌʻō. The eruption that followed lasted until September 2018. As of December 2020, it ranked as the twelfth-longest volcanic eruption on Earth since 1750. In 1986, activity moved down the rift to a new vent, Kūpaianahā, where it turned more effusive. It built a low, broad shield, and lava tubes carried flows 11 to 12 km to the sea.

  The human cost fell between 1986 and 1991. Lava cut the link between Chain of Craters Road and Hawaii Route 130. It consumed the community of Kapaʻahu, the village of Kalapana, and the subdivisions of Kālapana Gardens and Royal Gardens. It also engulfed the black sand beach at Kaimū. In 1992, the eruption returned to Puʻu ʻŌʻō and carried on in the same way. By the end of 2016, the east rift eruption had produced 4.4 km3 of lava and covered 144 km2. It had added 179 hectares to the island, destroyed 215 structures, and buried 14.3 km of highway beneath lava as thick as 35 m.

  A second eruption ran alongside it at the summit. On the 19th of March 2008, after months of rising sulfur dioxide and seismic tremor, a new vent opened in Halemaʻumaʻu. The explosion left a crater informally named the Overlook Crater, which belched a thick gas plume. On the 5th of September 2008, scientists saw a lava pond deep inside it for the first time. From February 2010 until May 2018 the pond was visible almost continuously, and lava briefly spilled onto the crater floor in April and May 2015, in October 2016 and in April 2018.

  In March 2018, the Hawaiian Volcano Observatory detected rapid inflation at Puʻu ʻŌʻō. On the 30th of April, the crater floor of the cone collapsed as magma moved underground into the lower Puna district. Hundreds of small earthquakes shook the east rift zone. On the 3rd of May, a 5.0 earthquake struck, new fissures opened, and lava began erupting in lower Puna, forcing evacuations from Leilani Estates and Lanipuna Gardens. A 6.9 earthquake followed on the 4th. By the 9th of May, 27 houses had been destroyed in Leilani Estates.

  On the 21st of May, two flows reached the Pacific, producing laze, a toxic cloud of hydrochloric acid and glass particles. By the 31st, lava had destroyed 87 houses and prompted evacuation orders for the town of Kapoho. By the 4th of June, it had crossed Kapoho and entered the sea. The tally of lost houses climbed from 159 to 533 and finally 657. The County of Hawaii ultimately reported 716 dwellings destroyed. The activity also destroyed Hawaii's largest natural freshwater lake, and lava poured into the ocean in three places.

  At the summit, the lava lake in Halemaʻumaʻu began dropping on the 2nd of May. The observatory warned that this raised the chance of steam explosions when magma met the water table, as had happened in 1924, and Hawaiʻi Volcanoes National Park closed. At about 4:15 a.m. on the 17th of May, an explosion sent ash 30,000 ft into the air. More explosions, large earthquakes and inward collapse of the crater continued until early August. The crater that remained was enlarged by the collapses, and several eruptions since 2020 have taken place inside it.

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• 6. A Lake, Then Fountains

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  In late July 2019, a lake of water appeared on the floor of Halemaʻumaʻu for the first time in over 200 years, fed by the rebounding water table. By the 1st of December 2020 it was about 49 m deep. Volcanologists were too wary to approach it, so they flew a drone over it in October 2019, January 2020 and December 2020 to study its gases. Later the drone sampled the plumes left after the lake boiled away.

  The boiling began at 9:30 p.m. on the 20th of December 2020, when three vents opened in the crater floor and replaced the lake with lava. The plume rose to 30,000 ft. Earthquake swarms on the 30th of November and the 2nd of December had given a warning, and the second was read as a small intrusion of magma. Within days the lava lake was 176 m deep, and by the 24th of February 2021 it reached 216 m. A spatter cone grew around the western vent. The supply of lava stopped between the 11th and the 13th of May, and on the 26th of May 2021 the eruption was declared over, with the lake 229 m deep.

  In August 2021, an earthquake swarm and increasing ground deformation led the observatory to raise the alert level from Yellow/Advisory to Orange/Watch. It lowered it again two days later. The real event came at 3:20 p.m. on the 29th of September 2021, when several fissures opened in the crater and fountains of lava rose more than 200 ft. As the lava lake rose, it partly drowned the vents and the fountains shrank. Overflight measurements on the 5th of October 2022 showed that 111 million cubic meters of lava had erupted and the crater floor had risen 143 m. The eruption paused on the 9th of December 2022.

  The pattern since then has been one of short, repeated bursts. Halemaʻumaʻu erupted again on the 5th of January 2023 and stopped 61 days later, on the 7th of March. A twelve-day episode ran from the 7th to the 19th of June 2023, and a third lasted from the 10th to the 16th of September. In 2024, a series of fissures on the upper southwest rift zone erupted shortly after midnight on the 3rd of June for about 8.5 hours. Another eruption followed from the 15th to the 20th of September, near Nāpau Crater in a remote, uninhabited part of the middle east rift, in four phases.

  The current eruption began within Halemaʻumaʻu on the 23rd of December 2024 and has proceeded in numbered episodes. Fountains reached 600 ft in March 2025, then 1,150 ft, and 1200 ft in July. Episode 35 produced the highest so far, at 1,500 ft. Episode 38 began on the 6th of December 2025 and was the most active phase to that point. By the end of the year, two vents on the southwestern floor of the crater had produced a total of 53 billion gallons of lava.

  Episode 40 began on the morning of the 12th of January 2026. Episode 41 lasted 8 hours and 18 minutes on the 24th of January, and Episode 42 lasted just under 10 hours on the 15th of February. Episode 43, on the 10th of March, ran about 9 hours and dropped heavy tephra across the national park. Winds carried ash, Pele's hair and tephra to Puna, Hilo and the Hamakua Coast, and officials raised alert levels, closed roads and issued ashfall warnings. Volcanologists call this style violent strombolian. It resembles the fountaining at Kīlauea Iki in 1959, Mauna Ulu in 1969 and Puʻu ʻŌʻō in 1983-86, and also the paroxysms of Etna.

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• 7. Life on the Slopes

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  More than 3,000 km separate Hawaii Island from the nearest continent, and that isolation shaped almost everything that lives on Kīlauea. Most species there are endemic. An estimated one-third of the island's natural flora and fauna is extinct, and the survivors remain vulnerable to invasive species and development. The first Ancient Hawaiians settled along the shore, where food and water were plentiful. Flightless birds with no experience of predators became a staple of their diet. Settlement caused many extinctions, particularly among birds, and it transformed the lowland forest into grassland. Fire played a part, but the main cause appears to have been the Polynesian rat.

  The volcano itself is a second threat. Lava flows burn through forest, and ash smothers plants. Layers of carbonized organic material at the bottom of ash deposits mark the destruction. In places the slopes show pristine montane forest beside volcanic deserts still waiting to be recolonized.

  The Kaʻū Desert, south of the southwestern rift zone, shows the extreme case. It is not a true desert, since more than 1000 mm of rain falls there each year. But the rain mixes with drifting volcanic sulfur dioxide to form acid rain with a pH as low as 3.4. Tephra particles make the soil very permeable, and plant life is practically nonexistent.

  The volcano's bulk also shapes the weather. Trade winds from the northeast are pushed upward by the mountain, which leaves the windward side wet and the leeward flank dry. The northern part of Kīlauea sits mostly below 1000 m and receives more than 75 in of rain a year. It is a lowland wet community. Farther south, with under 50 in of rain, it turns into lowland dry environment.

  In the wet north, Wao Kele o Puna covers 27785 acres, making it Hawaii's largest lowland wet forest reserve. Its main tree is ōhiʻa lehua, and rare plants there include hāpuʻu ferns and ʻieʻie vines, some of which help limit the spread of invasive species. The forest shelters the ʻōpeʻapeʻa, a bat, and the nananana makakiʻi, a spider. Many species there are thought to be undocumented. In the national park to the south, ʻōhiʻa trees and hāpuʻu ferns are common. The park hosts birds such as the ʻapapane, ʻiʻiwi and ʻelepaio, along with endangered species including the nēnē, the akiapōlāʻau and the ʻio. Along the coast, three of the island's nine known hawksbill sea turtle nesting sites lie, and the hawksbill is critically endangered.

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• 8. Watching the Mountain

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  After seeing the devastation of the 1908 Messina earthquake near Mount Etna in Italy, Thomas Jaggar, head of geology at the Massachusetts Institute of Technology, declared that volcanoes and earthquakes needed systematic study. He chose Kīlauea as the first site. With funding from MIT and the University of Hawaiʻi, he founded the Hawaiian Volcano Observatory in 1912, the first permanent installation of its kind in the United States. Jaggar directed it from 1912 to 1940. When the initial money ran out, the National Weather Service, the USGS and the National Park Service funded it in turn, and the USGS reclaimed it after 1946. The facility on the northwest rim of Kaluapele served until 2018, when volcanic activity damaged it beyond repair. Its buildings were torn down in 2024.

  The same terrain trained astronauts. NASA used the area to teach Apollo crews to recognize volcanic features, plan traverses, collect samples and take photographs, in sessions in April 1969, April 1970, December 1970, December 1971 and June 1972. Astronauts of Apollo 12, 14, 15, 16 and 17 later applied that training on the Moon. One of the geologist instructors was William R. Muehlberger.

  Research continues to find new uses for the volcano's signals. In 2022, researchers reported that Kīlauea's seismic waves, which can last for tens of seconds, could help predict future outbreaks. They studied thousands of events from seismic sensors, GPS stations and lake height observations. They found that magma temperature was associated with the duration of the seismic signal and with the quantity and composition of gas bubbles.

  The stakes are real. In 2018, the USGS National Volcanic Threat Assessment gave Kīlauea an overall threat score of 263, ranking it the volcano most likely in the United States to threaten lives and infrastructure.

  Tourists have visited since the 1840s. Businessmen such as Benjamin Pitman and George Lycurgus ran hotels at the rim, including Volcano House, which is still the only hotel or restaurant inside Hawaiʻi Volcanoes National Park. Lorrin A. Thurston, who invested in rim hotels and owned the Honolulu Advertiser, used editorials to campaign for a park. He boosted an idea proposed by William Richards Castle, Jr. By 1911, Governor Walter F. Frear had proposed a draft bill for a "Kilauea National Park". Endorsements arrived from John Muir, Henry Cabot Lodge and former President Theodore Roosevelt, who sided against local ranchers. Delegate Jonah Kūhiō Kalanianaʻole introduced several legislative attempts. President Woodrow Wilson signed House Resolution 9525 on the 1st of August 1916. It created the country's 11th national park and the first in a Territory.

  The park began as Hawaii National Park and was split from Haleakala National Park on the 22nd of September 1960. It became a World Heritage Site in 1987. Tourism to the islands had already exploded around 1959 with jet airliner travel, and Kīlauea, one of the few chronically erupting volcanoes, was a major draw. Today roughly 2.6 million people visit each year, and the Crater Rim Trail around the volcano is a National Recreation Trail.

  The Thomas A. Jaggar Museum, on the edge of Kaluapele, once offered the best sheltered view of Halemaʻumaʻu. It closed permanently after earthquakes from the 2018 eruptions damaged the building. In May 2025, the National Park Service reopened the public viewing area at Uēkahuna on the caldera rim, the former site of the observatory facilities and the museum.

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