Kīlauea

Location of Kīlauea on Hawaiʻi island

Like all Hawaiian volcanoes, Kīlauea was created as the Pacific tectonic plate moved over the Hawaiian hotspot in the Earth's underlying mantle.[12] The Hawaii island volcanoes are the most recent evidence of this process that, over 70 million years, has created the 6,000 km (3,700 mi)-long Hawaiian–Emperor seamount chain.[13] The prevailing, though not completely settled, view is that the hotspot has been largely stationary within the planet's mantle for much, if not all of the Cenozoic Era.[13][14] However, while the Hawaiian mantle plume is well understood and extensively studied, the nature of hotspots themselves remains fairly enigmatic.[15]

Kīlauea is one of five subaerial volcanoes that make up the island of Hawaiʻi, created by the Hawaiian hotspot.[16] The oldest volcano on the island, Kohala, is more than a million years old,[17] and Kīlauea, the youngest, is believed to be between 300,000 and 600,000 years of age;[16] Kamaʻehuakanaloa (formerly Lōʻihi), on the island's flank, is younger and has yet to breach the surface.[18] Thus Kilauea is the second youngest volcano in the Hawaiian–Emperor seamount chain, a chain of shield volcanoes and seamounts extending from Hawaii to the Kuril–Kamchatka Trench in Russia.[19]

Following the pattern of Hawaiian volcano formation, Kīlauea started as a submarine volcano, gradually building itself up through underwater eruptions of alkali basalt lava before emerging from the sea with a series of explosive eruptions[20] about 50,000 to 100,000 years ago. Since then, the volcano's activity has likely been as it is now, a continual stream of effusive and explosive eruptions of roughly the same pattern as its activity in the last 200 or 300 years.[21]

At most 600,000 years old, Kīlauea is still quite young for a Hawaiian volcano;[16] the oldest volcano on the island, the northwestern Kohala, experienced almost 900,000 years of activity before going extinct.[17] The volcano's foreseeable future activity will likely be much like it has been for the past 50,000 to 100,000 years; Hawaiian and explosive activity will make Kīlauea taller, build up its rift zones, and fill and refill its summit caldera.[21]

Simulated true-color Landsat mosaic

Kīlauea's summit caldera; volcanic gas can be seen rising out of Halemaʻumaʻu, within the caldera (January 2012)

Kīlauea has been active throughout its history.[21] Since 1918, Kīlauea's only prolonged period of rest was an 18-year pause between 1934 and 1952.[22] The bulk of Kīlauea consists of solidified lava flows, intermittent with scattered volcanic ash and tephra sourced from relatively lower-volume explosive eruptions.[21] Much of the volcano is covered in historical flows, and 90 percent of its surface dates from the last 1,100 years.[23] Kīlauea built itself up from the seafloor over time, and thus much of its bulk remains underwater;[20] its subaerial surface is in the form of a gently sloping, elongate, decentralized shield with a surface area of approximately 1,500 km² (579 sq mi),[24] making up 13.7 percent of the island's total surface area.[16]

Kīlauea lacks a topographical prominence, appearing only as a bulge on the southeastern flank of the nearby Mauna Loa; because of this, both native Hawaiians and early geologists considered it an active satellite of its more massive neighbor. However, analysis of the chemical composition of lavas from the two volcanoes shows that they have separate magma chambers, and are thus distinct. Nonetheless, their proximity has led to a historical trend in which high activity at one volcano roughly coincides with low activity at the other. When Kīlauea lay dormant between 1934 and 1952, Mauna Loa became active, and when the latter remained quiet from 1952 to 1974, the reverse was true. This is not always the case; the 1984 eruption of Mauna Loa started during an eruption at Kīlauea, but had no discernible effect on the Kīlauea eruption, and the ongoing inflation of Mauna Loa's summit, indicative of a future eruption, began the same day as new lava flows at Kīlauea's Puʻu ʻŌʻō crater. In 2002, Kilauea experienced a high-volume effusive episode at the same time that Mauna Loa began inflating. This unexpected communication is evidence of crustal-level interactions between Mauna Loa and Kīlauea, even though these two volcanoes are thought to be fairly independent of each other.[25] Geologists have suggested that "pulses" of magma entering Mauna Loa's deeper magma system may have increased pressure inside Kīlauea and triggered the concurrent eruptions.[26]

Kīlauea has a large summit caldera, measuring 4 by 3.2 km (2.5 by 2.0 mi) with walls up to 120 m (400 ft) high, breached by lava flows on the southwestern side.[22] It is unknown if the caldera was always there or if it is a relatively recent feature, and it is possible that it has come and gone throughout Kīlauea's eruptive history.[21] What is known is that the summit caldera likely formed over several centuries, with its construction estimated to have begun about 500 years ago,[27] and its present form was finalized by a particularly powerful eruption in 1790.[21] A major feature within the caldera is Halemaʻumaʻu, a large pit crater and one of Kīlauea's most historically active eruption centers. The crater is approximately 920 m (3,018 ft) in diameter and 85 m (279 ft) deep, but its form has varied widely through its eruptive history; the floor of Halemaʻumaʻu is now mostly covered by flows from its 1974 eruption.[28]

Kīlauea has two rift zones radiating from its summit, one leading 125 km (78 mi) out to the east, the other 35 km (22 mi) long and trending towards the southwest.[21] A series of fault scarps connecting the two rift zones form the Koa'e Fault Zone. Tectonic extension along both rift zones is causing Kīlauea's bulk to slowly slide seaward off its southern flank at a rate of about 6 to 10 cm (2 to 4 in) per year, centered on a basal décollement fault 7 to 9 km (4 to 6 mi) beneath the volcano's surface.[29] The eastern rift zone in particular is a dominant feature on the volcano; it is almost entirely covered in lava erupted in the last 400 years, and at its crest near the summit is 2 to 4 km (1 to 2 mi) wide.[24] Non-localized eruptions, typical of rift zone activity,[21] have produced a series of low-lying ridges down the majority of the east rift zone's length.[24] Its upper segment is the most presently active section of the volcano,[23][27] and is additionally the site of a number of large pit craters;[30] its lower extremity reaches down Kīlauea's submerged flank to a depth of more than 5,000 m (16,400 ft).[27] By contrast, the much smaller southwestern rift has been quiet since a rifting episode in 1974, and to date, has not been involved in the current eruptive cycle at all.[29] The southwestern rift zone's extremity is also underwater, although its submarine length is more limited. The southwestern rift zone also lacks a well-defined ridge line or a large number of pit craters, evidence that it is also geologically less active than the eastern rift zone.[27]

A prominent structure on Kīlauea's southern flank is the Hilina fault system, a highly active fault slipping vertically an average of 2 to 20 mm (1⁄16 to 13⁄16 in) per year along the system. Its physiographic province is 500 m (1,640 ft) deep, but it is unknown whether it is a shallow listric fault or if it penetrates to the very base of the volcano.[12] In connection with the 2018 lower Puna eruption the Hawaiian Volcano Observatory published some facts leading to the conclusion, that a catastrophic collapse would be incredibly remote.[31] A number of cinder cones, satellite shields, lava tubes, and other eruptive structures also dot the volcano, evidence of its recent activity.[30] Kīlauea has some interactions with Mauna Loa, its larger neighbor and only other recently active volcano on the island; interspersed lava flows and ash deposits belonging to its neighbor have been found on its flanks, and some of Mauna Loa's flows are, in turn, blanketed in Kīlauea tephra. In particular, the saddle between the two volcanoes is currently depressed, and is likely to fill over in the future.[27]

All historical eruptions at Kīlauea have occurred at one of three places: its summit caldera, its eastern rift zone, or its southwestern rift zone.[16] Half of Kīlauea's historical eruptions have occurred at or near Kīlauea's summit caldera. Activity there was nearly continuous for much of the 19th century, capped by a massive explosive eruption in 1924, before petering out by 1934. Recent activity has mostly shifted to Kīlauea's eastern rift zone, the site of 24 historical eruptions, located mostly on its upper section; by contrast, the volcano's southwestern rift zone has been relatively quiet, and has only been the site of five events to date.[21]

Rainbow and volcanic ash with sulfur dioxide emissions from Halemaʻumaʻu (April 2008)

Geologists have dated and documented dozens of major eruptions over the volcano's long history, bridging the long gap between Kīlauea's oldest known rock and only extremely recent written records and historical observation.[32] Historical lava flows from the volcano are generally recovered by scientists in one of three ways. The oldest flows, dating back 275,000 to 225,000 years, have been recovered from Kīlauea's submerged southern slope by ship-towed remotely operated vehicles. These lavas exhibit forms characteristic of early, submerged preshield-stage eruptive episodes, from when the volcano was still a rising seamount that had not yet breached the ocean surface,[33] and their surface exposure is unusual, as in most other volcanoes such lavas would have since been buried by more recent flows.[12]

The second method of recovering older rock is through the drilling of deep core samples; however, the cores have proved difficult to date, and several samples from depths of around 1,700 m (5,600 ft) that suggested dates as old as 450,000 years have since been found erroneous. More reliable paleomagnetic dating, limited to rocks dating from after Kīlauea's emergence from the sea, has suggested ages of around 50,000 years. Exposed flows above sea level have proved far younger. Some of the oldest reliably dated rock, 43,000 years old, comes from charcoal sandwiched beneath an ash layer on a fault scarp known as Hilina Pali; however, samples dated from higher up the scarp indicate ash deposition at an average rate of 6 m (20 ft) per thousand years, indicating that the oldest exposed flows, from the base of the feature, could date back as far as 70,000 years.[33] This date is similar to that of the oldest dated extant lava flow, a southwestern rift zone flow with an uncorrected radiocarbon dating of approximately 4650 BC.[32]

The oldest well-studied eruptive product from Kīlauea is the Uwēkahuna Ash Member, the product of explosive eruptions between 2,800 and 2,100 years ago. Although it has since been largely buried by younger flows, it remains exposed in some places, and has been traced more than 20 km (12 mi) from the volcano's caldera, evidence of very powerful eruptions. Evidence suggests the existence of an active eruptive center at this time, termed the Powers Caldera, whose fractures and faults lie 2 km (1 mi) outside the modern caldera. At least 1,200 years ago, lava from the Powers Caldera overtopped its rim and solidified the structure; this was followed by a period of very voluminous tube-fed pāhoehoe flows from the summit. Following cessation of activity around 400 years ago, eruptions re-centered on the eastern part of Kīlauea's summit, and concurrently activity increased at the northern end of the eastern rift zone.[27]

The earliest reliable written records of historical activity date back to about 1820,[34] and the first well-documented eruption occurred in 1823, when the volcano was first put under observation;[21] although Native Hawaiians are thought to have first settled on the island around 1,500 years ago, oral records predating European arrival on the island are few and difficult to interpret.[27] One pre-contact eruption in particular, a phreatomagmatic event in 1790,[22] was responsible for the death of a party of warriors, part of the army of Keōua Kuahuʻula, the last island chief to resist Kamehameha I's rule; their death is evidenced by a set of footprints preserved within the Hawai‘i Volcanoes National Park which are listed on the National Register of Historic Places.[34] Kīlauea has been the site of 61 separate eruptions since 1823, easily making it one of the most active volcanoes on Earth.[16][22]

Kīlauea's upper sulphur bank; painting by British geologist James Gay Sawkins, 1855

During its observed history, the volume of lava erupted by Kīlauea has varied widely. In 1823 Kīlauea's summit caldera was far deeper than it is today, but was in the process of filling up under nearly continuous summit eruption, with 3 km³ (1 cu mi) of lava erupted there alone by 1840. The period between 1840 and 1920 saw approximately half that in eruptive volume, and in the thirty years between then and about 1950, the volcano was unusually quiet and exhibited very little activity; Kīlauea's eruptive volume has increased steadily since then, with present activity comparable to that of the early 1800s.[21]

The length and origin of these eruptions have also varied. Events last anywhere between days and years, and occur at a number of different sites. Half of all eruptions occur at or near Kīlauea's summit caldera. Activity there was nearly continuous for much of the 19th century, and after a reprieve between 1894 and 1907, continued onwards until 1924. There have been five historical eruptions at the volcano's relatively quiet southwestern rift zone, and 24 along its more active eastern rift zone, mostly along its upper section.[21]

The volcano's observed history has mostly been one of effusive eruptions; however, this is a relatively recent occurrence. Prior to the arrival of the first Europeans on the island, Kīlauea was the site of regular explosive activity, evidenced then by tribal chants referencing the volcano's fickle nature, and today by geological records of an explosively active mode of past activity. Although explosive activity still occurs at the volcano, it is not as intense as it once was, and the volcano would become much more dangerous to the general public if it returned to its old phase of activity once more.[35]

Kīlauea erupted in 1823 and 1832, but the first major eruption since the 1790 event occurred in 1840, when its eastern rift zone became the site of a large, effusive Hawaiian eruption over 35 km (22 mi) of its length, unusually long even for a rift eruption.[36] The eruption lasted for 26 days and produced an estimated 205 to 265 million cubic meters of lava;[22] the light created by the event was so intense that one could reportedly read a newspaper in Hilo at night, 30 km (19 mi) away.[36]

Painting of the 1891 eruption

The volcano was active again in 1868, 1877, 1884, 1885, 1894, and 1918,[22] before its next major eruption in 1918–1919. Halemaʻumaʻu, then a small upwelling in the caldera floor, was topped by a lava lake that then drained, before refilling again, forming an enormous lava lake and nearly reaching the top edge of the caldera before draining once more. This activity eventually gave way to the construction of Mauna Iki, building up the large lava shield on the volcano's southwest rift zone over a period of eight months. The eruption also featured concurrent rift activity and a large amount of lava fountaining.[37]

Activity in 1921–1923 followed.[22] The next major eruption occurred in 1924. Halemaʻumaʻu, a fully formed pit crater after the 1919 event and the site of a sizable lava lake, first drained, then quickly began sinking into the ground, deepening to nearly 210 m (689 ft) beneath a thick cloud of volcanic ash. Explosive activity began on May 10 of that year, blowing rock chunks weighing as much as 45 kg (99 lb) 60 m (197 ft) out, and smaller fragments weighing about 9 kg (20 lb) out as far as 270 m (886 ft), and, after a brief reprieve, intensified through a major blast on May 18, when an enormous explosive event caused the eruption's only fatality. The eruption continued and formed numerous eruption columns up to and beyond 9 km (6 mi) in height, before slowly petering down and ending by May 28.[35][38] Volcanic activity was soon confined to the summit, and ceased completely after 1934.[22]

The Mauna Ulu eruption of 1969 generated a 300-metre (1,000 ft)-high lava fountain

After the Halemaʻumaʻu event, Kīlauea remained relatively quiet, and for a time, completely silent, with all activity confined to the summit.[22] The volcano came alive again in 1952, with an enormous lava fountain 245 m (800 ft) high at Halemaʻumaʻu. Multiple continuous lava fountains between 15 and 30 m (50 and 100 ft) persisted, and the eruption lasted 136 days.[39] Eruptions occurred soon after in 1954, 1955, and 1959, capped by a large event in 1960, when fissure-based phreatic eruption and earthquake activity gave way to a massive ʻaʻā flow that overran multiple evacuated communities and resorts; the resulting summit deflation eventually caused the ever-active Halemaʻumaʻu to collapse even further.[40]

From 1960 on, eruptive events occurred frequently until August 2018. The period 1967–1968 saw a particularly large, 80-million-cubic-meter, 251-day event from Halemaʻumaʻu.[22] This event was superseded the very next year by the marathon Mauna Ulu eruption, a large effusive eruption which lasted from May 24, 1969, to July 24, 1974, and added 230 acres (93 ha) of new land to the island. After eruptive activity had died down, there was a magnitude 7.2 earthquake that caused a partial summit collapse, after which activity did not resume at Kīlauea until 1977.[41] At the time, Mauna Ulu was the longest flank eruption of any Hawaiian volcano in recorded history. The eruption created a new vent, covered a large area of land with lava, and added new land to the island. The eruption started as a fissure between two pit craters, ʻĀloʻi and ʻAlae, where the Mauna Ulu shield would eventually form. Both pāhoehoe and ʻaʻā lava erupted from the volcano. Early on, fountains of lava burst out as much as 540 meters (1772 ft) high. In early 1973, an earthquake occurred that caused Kīlauea to briefly stop erupting near the original Mauna Ulu site and instead erupt near the craters Pauahi and Hiʻiaka.[41]

Puʻu ʻŌʻō at dusk, June 1983

The longest major eruption observed at Kīlauea in modern history occurred from January 1983 to September 2018. It had the longest duration of any observed eruption at this volcano. As of December 2020, it is the twelfth-longest duration volcanic eruption on Earth since 1750.[42] The eruption began on January 3, 1983, along the eastern rift zone. The vent produced vigorous lava fountains that quickly built up into the Puʻu ʻŌʻō cone, sending lava flows down the volcano's slope.

In 1986, activity shifted down the rift to a new vent, named Kūpaʻianahā, where it took on a more effusive character. Kūpaʻianahā built up a low, broad volcanic shield, and lava tubes fed flows extending 11 to 12 km (about 7 mi) to the sea. Between 1986 and 1991, the connection between Chain of Craters Road and Hawaii Route 130 was cut, and the community of Kapa’ahu, the village of Kalapana, and the subdivisions of Kālapana Gardens and Royal Gardens were lost to the lava.[43] A black sand beach at Kaimū was also engulfed.[44] In 1992, the eruption moved back to Puʻu ʻŌʻō, but continued in the same manner, covering nearly all of the 1983–86 lava flows and large areas of coastline.[45]

As of the end of 2016, the east rift zone eruption had produced 4.4 km³ (1 cu mi) of lava, covered 144 km² (56 sq mi) of land, added 179 ha (442 acres) of land to the island, destroyed 215 structures, and buried 14.3 km (9 mi) of highway under lava as thick as 35 m (115 ft).[46]

In addition to the nearly continuous activity at Puʻu ʻOʻo and other vents on the east rift zone, a separate eruption began at Kilauea's summit in March 2008. On March 19, 2008, following several months of increased sulfur dioxide emissions and seismic tremor, a new vent opened at Halemaʻumaʻu at Kilauea's summit in an explosive eruption. Following this event, the new crater formed in the explosion, informally named the "Overlook Crater," emitted a thick gas plume that obscured views into the vent. Several other explosive events occurred at the vent throughout 2008.[47]

On September 5, 2008, scientists observed a lava pond deep within the Overlook Crater for the first time. Beginning in February 2010, a lava pond was visible at the bottom of the crater almost continuously through the beginning of May 2018. Lava briefly overflowed the vent onto the floor of Halemaʻumaʻu in April and May 2015, October 2016, and April 2018.[47][48][49]

Lava from a fissure slowly advanced to the northeast on Hoʻokupu Street in Leilani Estates subdivision (May 5, 2018)

Beginning in March 2018, Hawaiian Volcano Observatory began to detect rapid inflation at Pu‘u ‘Ō‘ō,[50] leading scientists to warn that the increased pressure could lead to the formation of a new vent at Kilauea.[51]

Following weeks of increased pressure, the crater floor of the cone of Puʻu ʻŌʻō collapsed on April 30, 2018, as magma migrated underground into the lower Puna region of Kilauea's lower east rift zone.[52] Over the next few days, hundreds of small earthquakes were detected on Kīlauea's East rift zone, leading officials to issue evacuation warnings. On May 3, 2018, new fissures formed, and lava began erupting in lower Puna after a 5.0 earthquake earlier in the day, causing evacuations of the Leilani Estates and Lanipuna Gardens subdivisions.[53][54]

A seemingly related 6.9 magnitude earthquake occurred on May 4.[55] By May 9, 27 houses had been destroyed in Leilani Estates.[56][57]

Kilauea Volcano Fissure 8 captured on May 3rd, 2019

By May 21, two lava flows had reached the Pacific Ocean, creating thick clouds of laze (a toxic lava and haze cloud), which is made up of hydrochloric acid and glass particles.[58]

By May 31, 87 houses in Leilani Estates and nearby areas had been destroyed by lava. Advancing lava flows caused additional evacuation orders, including the town of Kapoho.[59][60] By June 4, with the lava having crossed through Kapoho and entered the ocean, the confirmed number of houses lost had reached 159.[61] Two weeks later, the confirmed number of homes lost was 533,[62] and as of June 25 it had risen to 657.[63]

Two views of Halemaʻumaʻu from roughly the same vantage point. At left is the view from 2008, with a distinct gas plume from the Overlook vent, the location of what would become a long-lived lava lake. At right is a view of Halemaʻumaʻu after the eruptive events of 2018, showing the collapsed crater.

Together with the outbreak of lava in lower Puna, a lava lake at Halemaʻumaʻu at Kilauea's summit began to drop on May 2, 2018.[52] The Hawaiian Volcano Observatory warned that the lowering of the lava lake increased the potential for phreatic (steam) explosions at the summit caused by interaction of magma with the underground water table, similar to the explosions that occurred at Halemaʻumaʻu in 1924. These concerns prompted the closure of Hawaiʻi Volcanoes National Park.[64] On May 17, at approximately 4:15 a.m., an explosive eruption occurred at Halemaʻumaʻu, creating a plume of ash 30,000 feet into the air.[65] This marked the beginning of a series of vigorous explosions that produced significant ash plumes from Halemaʻumaʻu.[66] These explosions, accompanied by large earthquakes and inward slumping and collapse within and around Halemaʻumaʻu, continued until early August.[67][68]

In late July 2019, a water lake appeared on the bottom of Halemaʻumaʻu for the first time in over 200 years,[69] as water from the rebounding water table began entering the crater. Afterward, the crater lake gradually grew in size.[70] On December 1, 2020, the lake was approximately 49 metres (161 ft) deep.[71] Within a month, the water lake would be replaced by a lava lake during the new eruption.

View of the eruption from outside the summit caldera, on December 20, 2020

On December 20, 2020, at 9:30 PM local time, an eruption broke out within Halemaʻumaʻu at Kīlauea's summit caldera. The US Geological Survey's Hawaiian Volcano Observatory reported that three vents were feeding lava into the bottom of Halemaʻumaʻu Crater, boiling off the water lake that had been growing since summer 2019 and replacing it with a lava lake.[72] The eruption created a plume that reached 30,000 feet (9,144 m) in elevation. The eruption was preceded by earthquake swarms centered at Kīlauea Caldera on November 30, 2020, and December 2, 2020, the second of which was interpreted as a small intrusion of magma.[8] By the following morning, emergency officials reported that the eruption had stabilized and that two of the three vents remained active and continued to fill the floor of Halemaʻumaʻu with lava.[73] By 7:30 a.m. on December 25, 2020, the lava lake had filled in 176 metres (577 ft) of the crater, and the level of the lake was continuing to rise.[74] On January 8, 2021, the depth of the lava lake had increased to 636 feet (194 m).[75] By February 24, the depth of the lava lake in the western, active portion had increased to 216 metres (709 ft). A spatter cone had also formed around the western vent.[76]

The eruption continued for another few months, though activity steadily decreased. On May 26, 2021, the Hawaiian Volcano Observatory announced that Kīlauea was no longer erupting. Lava supply to the lava lake appeared to have ceased between May 11 and May 13, and the lava lake had completely crusted over by May 20. The last surface activity in Halemaʻumaʻu was observed on May 23.[77][78] At the time activity ceased, the lava lake was 229 metres (751 ft) deep.[79]

On August 23, 2021, the Hawaiian Volcano Observatory raised Kīlauea's alert status from "Yellow/Advisory" to "Orange/Watch" due to an earthquake swarm and a concurrent increase in ground deformation at the volcano's summit. The observatory stated that the activity potentially indicated "the shallow movement of magma beneath the south part of Kīlauea caldera."[80] The observatory lowered Kīlauea's alert status back to "Yellow/Advisory" two days later after the earthquake swarm and ground deformation waned.[81]

The Hawaiian Volcano Observatory began to record increased earthquake activity and changes in ground deformation patterns at Kīlauea's summit at about noon local time on September 29, 2021.[82] An eruption began at 3:20 p.m. local time when several fissures opened within Halemaʻumaʻu crater in Kīlauea's summit caldera.[83] During the initial stages of the eruption, lava erupted in fountains more than 200 feet (61 m) tall, though the height of the fountains declined as the level of lava in the crater rose, partially drowned the erupting vents.[84]

As of October 30, 2022, lava continues to erupt at Halemaʻumaʻu. Overflight measurements from October 5, 2022, indicated that 111 million m³ (29 billion U.S. gal) of lava had been effused, and that the floor of Halemaʻumaʻu had risen 143 meters (469 ft), since the beginning of this eruption on September 29, 2021.[85][86]

In 2018, the United States Geological Survey National Volcanic Threat Assessment gave Kīlauea an overall threat score of 263, and ranked it first among volcanoes in the United States most likely to threaten lives and infrastructure.[87]

There was concern that the presence of a water lake in Halemaʻumaʻu following the 2018 summit collapse meant that Kīlauea's next summit eruption might be explosive if magma rose rapidly to the surface.[70] However, when Kīlauea erupted in December 2020, the eruption was non-explosive in nature, with three vents feeding magma into the lake and boiling off the water.

The Global Volcanism Program has assigned a Volcanic Explosivity Index (VEI; the higher the number, the more explosive) to all except six of Kīlauea's ninety-six known eruptions of the last 11,700 years. The eruption of 1790 has a VEI of 4.[88] The 1983–2018 eruption has a VEI of 3.[89] The eruptions of 1820, 1924, 1959 and 1960 have a VEI of 2. The eruptions of 680, 1050, 1490, 1500, 1610, 1868 and four eruptions in 1961 have a VEI of 1. The other seventy-four eruptions have a VEI of 0.[88]

ʻŌhiʻa (Metrosideros polymorpha) growing on a barren lava field dating from 1986, formerly the village of Kalapana, Hawaii. The myrtle in this picture, taken in 2009, may have since been covered over—fresh flows in 2010 partially re-covered the area.

Because of its position more than 3,000 km (1,864 mi) from the nearest continental landmass, the island of Hawaiʻi is one of the most geographically isolated landmasses on Earth; this in turn has strongly influenced its ecology. The majority of the species present on the island are endemic to it and can be found nowhere else on Earth, the result of an isolated evolutionary lineage sheltered from external biotic influence; this makes its ecosystem vulnerable both to invasive species and human development, and an estimated third of the island's natural flora and fauna has already gone extinct.[90]

Kīlauea's ecological community is additionally threatened by the activity of the volcano itself;[30] lava flows often overrun sections of the volcano's forests and burn them down, and volcanic ash distributed by explosive eruptions often smothers local plant life. Layers of carbonized organic material at the bottom of Kīlauea ash deposits are evidence of the many times the volcano has wrought destruction on its own ecosystem and that of its neighbor Mauna Loa, and parts of the volcano present a dichotomy between pristine montane forest and recently buried volcanic "deserts" yet to be recolonized.[91]

Kīlauea's bulk affects local climate conditions through the influence of trade winds coming predominantly from the northeast, which, when squeezed upwards by the volcano's height, result in a moister windward side and a comparatively arid leeward flank. The volcano's ecology is further complicated by height, though not nearly as much as with its other, far taller neighbors, and by the local distribution of volcanic products, making for varied soil conditions. The northern part of Kīlauea is mostly below 1,000 m (3,281 ft) and receives more than 75 in (191 cm) mean annual rainfall, and can mostly be classified as a lowland wet community; farther south, the volcano has squeezed out much of the precipitation and receives less than 50 in (127 cm) mean annual rainfall, and is considered mostly a lowland dry environment.[92]

The 'amakihi (Chlorodrepanis virens) is one of the many birds that live on the volcano's flanks.

Much of Kīlauea's southern ecosystem lies within the Hawaiʻi Volcanoes National Park, where a’e ferns, ʻōhiʻa trees (Metrosideros polymorpha), and hapu’u of the genus Cibotium are common.[93] The park hosts a large variety of bird species, including the 'apapane (Himatione sanguinea); the 'amakihi (Hemignathus virens); the 'i'iwi (Vestiaria coccinea); the ‘ōma’o (Myadestes obscurus), the ʻelepaio (Chasiempis sp.); and the endangered 'akepa (Loxops coccineus), 'akiapola'au (Hemignathus munroi), nēnē (Branta sandvicensis), ʻuaʻu (Pterodroma sandwichensis), and ʻio (Buteo solitarius) species.[94] The Kīlauea coast also hosts three of the nine known critically endangered hawksbill sea turtle (Eretmochelys imbricata) nesting sites on the island.[95]

Some of the area alongside Kīlauea's southwestern rift zone takes the form of the unusual Kaʻū Desert. Although not a "true" desert (rainfall there exceeds the maximum 1,000 mm (39 in) a year), precipitation mixing with drifting volcanic sulfur dioxide forms acid rain with a pH as low as 3.4, greatly hampering regional plant growth.[96] The deposited tephra particulates make the local soil very permeable. Plant life in the region is practically nonexistent.[97]

Kīlauea's northern lowland wet-forest ecosystem is partially protected by the Puna Forest Reserve and the Kahauale`a Natural Area Reserve. At 27,785 acres (11,244 ha), Wao Kele in particular is Hawaiʻi's largest lowland wet forest reserve, and is home to rare plant species including hāpuʻu ferns (Cibotium spp.), 'ie'ie vines (Freycinetia arborea), and kōpiko (Psychotria mariniana), some of which play a role in limiting invasive species' spread. ʻOpeʻapeʻa (Lasiurus cinereus semotus) ʻio (Buteo solitarius), common ʻamakihi (Hemignathus virens), and nananana makakiʻi (Theridion grallator) live in the trees. There are thought to be many more as-yet-undocumented species within the forest.[98][99] Wao Kele's primary forest tree is ʻōhiʻa lehua (Metrosideros polymorpha).[100]

The first Ancient Hawaiians to arrive on Hawaii island lived along the shores, where food and water were plentiful.[101] Flightless birds that had previously known no predators became a staple food source.[102] Early settlements had a major impact on the local ecosystem, and caused many extinctions, particularly amongst bird species, as well as introducing foreign plants and animals and increasing erosion rates.[103] The prevailing lowland forest ecosystem was transformed from forest to grassland; some of this change was caused by the use of fire, but the main reason appears to have been the introduction of the Polynesian rat (Rattus exulans).[104]

The summits of the five volcanoes of Hawaii are revered as sacred mountains. Hawaiians associated elements of their natural environment with particular deities. In Hawaiian mythology, the sky father Wākea marries the earth mother Papa, giving birth to the Hawaiian Islands.[102] Kīlauea itself means "spewing" or "much spreading" in Hawaiian, referencing its high state of activity,[16] and in Hawaiian mythology, Kīlauea is the body of the deity Pele, goddess of fire, lightning, wind, and volcanoes.[105] It is here that the conflict between Pele and the rain god Kamapuaʻa was centered; Halemaʻumaʻu, "House of the ʻamaʻumaʻu fern", derives its name from the struggle between the two gods. Kamapuaʻa, hard-pressed by Pele's ability to make lava spout from the ground at will, covered the feature, a favorite residence of the goddess, with fern fronds. Choked by trapped smoke, Pele emerged. Realizing that each could threaten the other with destruction, the other gods called a draw and divided the island between them, with Kamapuaʻa getting the moist windward northeastern side, and Pele directing the drier Kona (or leeward) side. The rusty singed appearance of the young fronds of the ʻamaʻumaʻu is said to be a product of the legendary struggle.[106]

This early era was followed by peace and cultural expansion between the 12th and late 18th century. Land was divided into regions designed for both the immediate needs of the populace and the long-term welfare of the environment. These ahupuaʻa generally took the form of long strips of land oriented from the mountain summits to the coast.[102]

Students collecting GPS data for the USGS in Kīlauea's eastern rift zone in 2015

The first foreigner to arrive at Hawaii was James Cook in 1778.[107] The first non-native to observe Kīlauea in detail was William Ellis, an English missionary who in 1823 spent more than two weeks trekking across the volcano. He collated the first written account of the volcano and observed many of its features, establishing a premise for future explorations of the volcano.[108]

Wikisource has original text related to this article:

The Volcano of
Ki-Rau-E-A,
a poem by L. E. L.

Another missionary, C. S. Stewart, U.S.N., wrote of it in his journal 'A Residence in the Sandwich Islands', which Letitia Elizabeth Landon quoted from in the notes to her poem 'The Volcano of Ki-Rau-E-A' in Fisher's Drawing Room Scrap Book, 1832.

One of the earliest and most important surveyors of Kīlauea was James Dwight Dana, who, staying with the missionary Titus Coan, studied the island's volcanoes in detail for decades first-hand.[109] Dana visited Kīlauea's summit and described it in detail in 1840.[110] After publishing a summary paper in 1852, he directed a detailed geological study of the island in 1880 and 1881 but did not consider Kīlauea a separate volcano, instead referring to it as a flank vent of Mauna Loa; it was not until another geologist, C. E. Dutton, had elaborated on Dana's research during an 1884 expedition that Kīlauea came to be generally accepted as a separate entity.[111]^{: 154–155}

Steam venting from fissures inside the caldera, October 2022

The next era of Kīlauea's history began with the establishment of the Hawaiian Volcano Observatory on the volcano's rim in 1912. The first permanent such installation in the United States, the observatory was the brainchild of Thomas Jaggar, head of geology at the Massachusetts Institute of Technology; after witnessing the devastation of the 1908 Messina earthquake near Mount Etna in Italy, he declared that something must be done to support systematic volcanic and seismic study, and chose Kīlauea as the site of the first such establishment. After securing initial funding from MIT and the University of Hawaii, Jaggar took directorship of the observatory and, whilst its head between 1912 and 1940, pioneered seismological and observational study and observation of active volcanoes.[112] After initial funding ran out, the Observatory was successively funded by the National Weather Service, the United States Geological Survey (USGS), and the National Park Service, before settling on the USGS, under whose banner the observatory has been operating since 1947. The main building has been moved twice since establishment, and today is positioned on the northwest rim of Kīlauea's caldera.[113]

NASA used the area to geologically train the Apollo Astronauts in recognizing volcanic features, planning traverses, collecting samples and taking photographs. Training took place in April 1969, April 1970, December 1970, December 1971, and June 1972. Astronauts of Apollo 12, Apollo 14, Apollo 15, Apollo 16 and Apollo 17 used this training on the Moon. Notable geologist instructors included William R. Muehlberger.[114]