Kilauea Volcano

Kilauea is located on the SE flank of Mauna Loa, on Big Island, Hawaii. However, Kilauea has its own magma system, distinct from that of Mauna Loa, and it thus a volcano of its own right. Kilauea, like Mauna Loa, is a shallow-sloped shield volcano. Eruptions of Kilauea occur at either the summit caldera, or along the rift zones. These mark areas in which parts of the volcano are gradually drifting apart and where magma can more easily reach the surface. The 35km long SW rift zone has shown little activity in recent years. Many of the ridges showing the location of this zone were created during an earthquake (7.9 on Richter scale) in 1868, after which magma pushing upwards widened many of them. The 125km E rift zone has been the site of much activity in the last century as shall be detailed below. The summit area consists of a large 3x5km caldera which contains a main pit crater known as Halema'uma'u. The summit caldera may have been formed after the massive explosive eruption of 1790 which rained pyroclastics on tribal warriors 10km from the summit, killing 80 of them. Notable historical eruptions are summarized below and provide an indication of the type of activity thought to have occurred at Kilauea since it gradually rose out of the sea 50-100000 years ago.

Annotated overview of Kilauea summit region.	Halema'uma'u crater (1040m) in Kilaueas summit caldera. Site of lava lake until 1924.

From 1823, when records began, until 1924, a large lava lake persisted in the Halema'uma'u crater. The lake had the following morphology. A semi-solid plug of lava ("epimagma") rested on top of the magma in the pipe-like main conduit. The plug had holes and fissures in it, through which more liquid lava ("pyromagma") could reach the surface. This formed fluctuating lakes of molten lava of varying depths and shapes on top of the plug. Parts of the epimagma protruded, giving the false impression of small islands floating in the lake. Small lava fountains could sometimes be observed much like at Erta Ale lava lake in recent years. The continuous circulation of liquid magma in and out of the lake due to convective forces in the conduit and tidal fluctuations is what defined it as a true lava like as opposed to a transient pool of lava.

The level of the lake (including the plug) could rise and fall rapidly, sometimes as much as 100m in a day. In 1924, the level dropped to about 200m below the rim and remained there during March and April. From April 29 to May 6, subsidence of the lake continued, leaving an over 200m deep pit. Between May 10 and May 28, Halemaumau entered into a phase of violent phreatomagmatic activity. The reduced height of the lake in the conduit is thought to have reduced the pressure acting outwards on the walls thereof, allowing entry of groundwater at an approximate depth of 500m. The groundwater was rapidly turned into highly pressurized pockets of steam by the magma in the conduit. Discharges of this pressure propelled hot but solidified material explosively out of the crater. Huge ballistic blocks weighing up to 10 tonnes were thrown to a kilometer from the crater and caused 1 fatality. Ash clouds rose rapidly up to 2km and then by gently convection to heights of over 7km. The eruption gradually increased in intensity with the most violent explosions being recorded on 18 May, before activity gradually sank again. The explosions widened the crater from a diameter of 450m to 1000m. No proper convecting lava lake has been able to establish itself in the crater since then although small amount of material have erupted on the crater floor. However, lava small lakes have been periodically observed in the Pu'u O'o crater in recent times.

Halema'uma'u crater (1040m) in Kilaueas summit caldera.	Halema'uma'u crater (1040m). Tourist vehicles at top left provide scale.

In 1959, a summit eruption at Kilauea Iki crater took place from November 14 to December 20. The eruption was characterized by periodic episodes of lava fountaining reaching heights of up to 580m and creating transient lava lakes up to 125m deep, after which massive drainbacks of the lakes into the vent could be observed. These drainbacks presumably kept refilling the magma chamber and allowed a longer persistence of the eruption. A total of 16 fountaining episodes were recorded with average lengths of 20 hours. The first and longest episode lasted for 167 hours and frequently reached heights of 300m.

Lava fountaining has been observed on numerous occasions at Kilauea and is generically referred to as Hawaiian activity. Discharge rates were over 1 million kg/s during a number of the Kilauea Iki fountaining episodes. The parameters and frequency of the fountaining phases of a number of eruptions at Kilauea are summarized in Houghton and Gonnermann, 2008 (Chemie der Erde 68, p.117-140). Hawaiian fountaining is only possible with basaltic lavas which are of relatively low viscosity. The mechanism causing the fountaining is disputed, with two main models having been put forward.

In the Rise Speed Dependent (RSD) model, the magma must rise relatively fast in the conduit so that bubbles of gas forming in it due to depressurization cannot rise fast relative to the magma. Consequently, the bubbles cannot merge into large gas pockets (as proposed for RSD-based strombolian eruption model) and the magma rises as a relatively homogenous 2-phase flow consisting of gas-rich magma. Continuous depressurization and gas formation (mainly water vapour according to the RSD model) drives the eruption, propelling a relatively steady fountain out of the conduit.

In the conflicting Collapsing Foam (CF) model, it is argued that a foam of gas accumulates near the roof of a magma chamber by exsolution of primarily carbon dioxide from the magma. When this accumulated gas starts to rise to the surface it forms a distinct (annular) flow from the rising magma, nevertheless frictionally dragging it to the surface of the conduit and expelling it in the form of a fountain.

The two models are compared in detail by Parfitt (a proponent of the RSD model) using data from eruptions at Kilauea (Parfitt 2004. J. Volc. Geotherm. Res. 134, p.77-107). It was concluded that patterns and relative volumes of carbon dioxide and water vapour release were more consistent with the RSD model for the eruptions of Pu'u O'o which were analysed in the paper. Whichever model is correct, the volumes of gas driving the eruptions are immense, with an estimated 40000 and 3200 tonnes/day of water vapour and carbon dioxide, respectively, being erupted during a relatively typical fountaining episode in March 1984.

Returning to the chronology of significant eruptions; in 1960, a fissure eruption along the E rift zone caused lava fountaining and extensive lava flows which eventually overran hastily erected earth walls and destroyed the town of Kapoho. 2 square km of fresh coastline were added to the island during this eruption.

From May 1969 till July 1974 (with a brief pause in 1971), another eruption of the E rift zone occurred and formed the new Mauna Ulu shield. Multiple periods of lava fountaining up to a maximum height of 540m were observed during the first months of the eruption. Lava flows reached the coast 12km away. The eruption continued with lesser episodes of fountaining and persistent flowing of lavas, mostly through tube systems, to the coastal region and into the sea.

Since 1983, Kilauea has again been in almost continuous eruption from the E rift zone. In 1983, a series of up to 470m high lava fountaining episodes, with gaps of up to a week inbetween, were observed along a new fissure. At the main site of this fountaining, the Pu'u O'o cone was rapidly built up. Activity persisted at this site until it shifted 3km further down the rift zone in 1986 where it rapidly formed a broad effusive shield known as Kupaianaha. The lava flow field around Kupaianaha gradually expanded until in November 1986 first flows were reaching the sea. From 1987 till 1989, most of the lava from Kupaianaha continued to enter the sea and build new land. In 1990, the flow directions shifted slightly and over 100 buildings in Kalapana were gradually buried in 15-25m of lava. In February 1992, activity returned to Pu'u O'o, which had been the site of a persistent lava pond since 1990. As the feeder system for Kupaianaha became gradually blocked, the height of the pond in Pu'u O'o began to rise. Activity at Pu'u O'o rapidly built a new shield on the W side of the original cone. Lava flowed from this shield and later again from vents inside Pu'u O'o through a system of tunnels towards the sea. Pu'u O'o eruption since 1983 has been similar in style to that witnessed at Kupaianaha before, being largely effusive and channelling large amounts of lava through mostly closed tube systems towards the sea. Collapses of parts of the original Pu'u O'o cinder cone, episodes of lava overflowing from the crater or breaking out of the tube system occasionally occur. The coastline has been reached over a width of over 15km.

On July 21, 2007 a shift in activity occurred from Pu'u O'o to a fissure extending eastwards from a point 150m to the E of Pu'u O'o. The fissure initially was erupting about 1 million cubic meters of lava per day from 4 sections, but after just over a week activity became focussed on the most easterly section of the fissure (section D). A 1km lava channel was formed rapidly and during the first weeks A'a lava flows extended as far as 6km from the vent in a NE direction. By November, overflows from the channel had built up the ground around it resulting in the flow being perched up to 30m above the surrounding lava fields. On 21. Nov. 2007, lava began to erupt from the S flank of the channel near the vent. This change in activity (known as the Thanksgiving Eve Breakout (TEB)) was associated with the sequential formation of a number of rootless shields in the following months. Each of these was formed at a point at which lava surfaced for a significant length of time. These shields (gently inclined mounds) are like miniature shield volcanoes without their own magma chambers. They can be considered equivalent to hornitos found over lava flows at other volcanoes with more viscous basaltic lavas. The shields formed over lava channels at points further and further away from the source. The largest shield is 40m high and has a diammeter of about 400m. The unstable shields are partially filled with molten lava and collapse of their walls can release large volumes which can rapidly flow. This occurred on 8, 26 Jan and 13 Feb 2008 and resulted in A'a flows reaching the outskirts of the Royal Garden Division (an abandoned settlement). By mid-february shield-building had ceased and instead Pahoehoe flows were extending towards Royal Garden Division (RGD). These entered RGD by Feb 24 and soon destroyed a couple of abandoned houses. By March 5 the flow reached the sea. Significant amounts of lava were flowing into the sea by July 2008, creating spectacular litoral explosions.

2008 has also seen the return activity to Halema'uma'u crater. In previous years degassing at Halema'uma'u has involved just under 200 tonnes/day of sulphur dioxide. By the beginning of 2008, levels reached 300 t/d and further increases took it up to 1000 t/d in Feb. By March 13 degassing became focussed at a new vent at the side of the crater and up to 2000 t/d were being released. On March 19 an explosion occurred at the vent and rocks up to a size of a meter were propelled out of the crater. A small crater was formed. No fresh lava was involved in this hydrothermal eruption, however on March 23 the gas plume from the vent turned darker due to entrainment of ash particles. These were both formed by degrading rock (lithic ash) in the vent and for the first time by injection of small amounts of fresh (juvenile) lava. On April 9, a second smaller explosion occurred and resulted in enlarging of the vent, followed by a third on April 16 which deposited a thin layer of pinkish ash composed of minute lithic and juvenile particles downwind of the crater. The large amounts of gas that continue to be erupted from the vent and the risk of further explosions has led to access restrictions in the vicinity of Halema'uma'u. Sulphur dioxide causes respiratory problems since it combines with moisture in the respiratory tract to form sulphuric acid.

(last updated July 29 2008)

For a more detailed chronology of eruptions at Kilauea and for current eruption updates, the reader is referred to the Hawaiian Volcano Observatory website (hvo.wr.usgs.gov/Kilauea).

Approaching Pu'u O'o crater, site of ongoing eruption since 1983.	View into Pu'u O'o crater, April 2005.

Vents on floor of Pu'u O'o crater.	Lava lake in East Pond Vent, Pu'u O'o crater, April 2005.

Lava fountain in East Pond Vent lava lake.	Pele's tears resulting from lava fountaining from East Pond Vent, Pu'u O'o (Scale in cm).

Three solidified lava toes.	Lava breaking out from under hardened crust and forming small new Pahoehoe flow.	Lava breaking out from under hardened crust.

Advancing lava toe.	Close-up of lava flow.

	Lava flows entering sea.

Kilauea covers a huge area. Visitors are mostly limited to the few trails and roads in the area. Visiting Pu'u O'o is not allowed although it is possible to fly over it by helicopter. The coastal flow planes are usually accessible and often allow fascinating close encounters with flowing lava, but visitors should take care since the ground is unstable and it is easy to lose orientation, especially after dark. A headlamp, compass or GPS, and lots of water are advisable. The coastline is not stable and collapses of lava benches may occur without warning. The flow fields around the shields are uneven and lava tubes may not be able to support your weight.

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