Sciency Thoughts: Holuhraun Lava Field

Showing posts with label Holuhraun Lava Field. Show all posts

Saturday, 16 July 2016

Understanding how caldera-collapse drove the 2014-15 Bárdarbunga eruption in Iceland.

Between August 2014 and February 2015 the Bárdarbunga volcanic system in Iceland underwent the largest volcanic eruption in Iceland (or anywhere else in Europe) since the 1783–1784 eruption on Mount Laki, producing 1.4 cubic kilometers of basaltic lava, not from the main caldera, which is burried beneath the Vatnajökull Ice Cap, but rather from the Holuhruan Vent Field, which is 48 km from the caldera and is connected to it by a network of fissures. During the course of this eruption the ice sheet above the caldera subsided by 65 m, leading volcanologists to conclude that the eruption was driven by the collapse of the caldera into the underlying magma chamber, only the seventh such eruption observed sinc the advent of seismic monitoring in the early twentieth century; the earlier cadera collapse eruptions being Katmai 1912, Fernandina 1969, Tolbachik 1976, Pinatubo 1991, Miyakejima 2000, and La Reunion 2007, all of which were substantial volcanic episodes.

Lava eruptiong from the Holuhruan Vent Field in Sepember 2014. Eggert Norddahl/Bergsveinn Norddahl/VolcanoCafe.

In a paper published in the journal Science on 15 July 2016, a team of scientists led by Magnús Gudmundsson of the Institute of Earth Sciences at the University of Iceland describe the results of a study of the 2014-15 Bárdarbunga eruption using data from seismic monitoring stations and aerial radar observations made of the caldera during the eruption.

The eruption began on 16 August 2014 with a series of small earthquakes beneath the southeastern part of the caldera, followed by the development of a new rift, which originally propagated to the southeast, reaching 7 km from the caldera within 15 hours. This rift then changed direction, migrating northeast and reachin the Holuhraun Vent Field in two weeks (the rift eventually spread to 41 km beyond the vent field). Material passing from the magma chamber through the rift reached the Holuhraun Vent Field on 31 August 2016, leading to the onset of the visible eruptive episode.

The loss of material into the new rift system led the magma chamber to begin to deflate, placing stress on the rocks around the margin of the caldera, which were now forced to support the weight of rock and ice above the chamber. On 23 August 2016 the first of a series of small tremors on the northern part of the rim as recorded, followed by the spreading of such activity around the rim over the next few days. This in turn was followed by substantial subsidance in the central part of the caldera, as new faults developed around the rim, enablimg a plug of material above the magma chamber to subside into the chamber. This in turn forced further magma out of the chamber and into the rift system, driving further volcanism on the Holuhraun Vent Field.

The Bárdarbunga caldera and the lateral magma flow path to the Holuhraun eruption site. (A) Aerial view of the ice-filled Bárdarbunga caldera on 24 October 2014, view from the north. (B) The effusive eruption in Holuhraun, about 40 km to the northeast of the caldera. (C) A schematic cross section through the caldera and along the lateral subterranean flow path between the magma reservoir and the surface. Gudmundsson et al. (2016).

Saturday, 10 October 2015

Sulphur Dioxide emissions from the 2014-15 Holuhraun Lava Field Eruption.

In mid-August 2014 seismic monitoring stations in Iceland began to record small Earth-tremors beneath the Bárðarbunga Volcano, which rises through the Vatnajökull Glacier in northern Iceland, Such seismic events are considered highly significant by volcanonolgists as they are often caused by magma moving into chambers beneath the volcano, and can therefore be an indicator of forthcoming eruptions. These tremors grew in size and frequency throughout the month, until on 31 August lava began to erupt from vents at the Holuhraun Lava Field (part of the Bárðarbunga-Veiðivötn Volcanic Complex) to the north of the Vatnajökull Glacier. This eruption continued through September 2015, producing a continuous eruption along a 1.5 km fissure with fountains of lava reaching 100 m in height. During the second half of the month the eruptive activity declined and became restricted to four craters along the fissure. Lava continued to be erupted from these craters at a declining rate until the end of February 2015. This eruption produced about 1.5 km³ of lava covering an area of about 85 km². This is the third recorded eruption at the Holuhraun Lava Field (previous eruptions having occurred in 1797 and 1862–1864), and the first flood lava eruption in Iceland since the Laki eruption of 1783-84.

Eruptions on the Holuhraun Lava Field in September 2014. Eggert Norðdahl/Volcano Café.

In a paper published in the Journal of Geophysical Research: Atmospheres on 21 August 2015, a team of scientists led by Anja Schmidt of the School of Earth and Environment at the University of Leeds describe the results of a study of sulphur dioxide emissions during the 2014-15 Holuhraun Lava Field eruption, and discuss the implications of this for future policy making in Europe.

Remote sensing of the volcanic emissions, both from ground stations and from satellites, detected Sulphur Dioxide plumes rising as high as 3 km above the visible eruption, and suggest that an average of 35 kilotons being emitted per day throughout the eruptive episode, with emissions in September 2014 reaching as high as 120 kilotons per day. This implies that throughout the eruptive episode the Holuhruan Lava Field was emitting more sulphur dioxide than the total produced by all 28 members European Environmental Agency from all sources including shipping during the entire of 2010. It also significantly outperformed other volcanoes noted for their high long term sulphur dioxide emissions, such as Kilauea in Hawaii (which emits about 2-8 kilotons of sulphur dioxide per day on average) and Mount Etna in Italy (which emits an average of 3.5 kilotons of sulphur dioxide per day). This represents the largest output of sulphur dioxide by a single volcano since the 2000-2003 Miyake-jima eruption in Japan, which was in turn thought to have been the largest emitter of sulphur dioxide since the Laki eruption of 1783-84, which caused a significant period of climatic stress and cooling in Europe in the 1780s.

Schmidt et al. attempted to model the progress of emissions from Holuhraun towards Europe in September 2014 using the NAME computer modelling system, which has previously been used by the London Volcanic Ash AdvisoryCentre to model emissions from the 2008 Kasatochi eruption, the 2009 Sarychev eruption and the 2010 Eyjafjallajökull eruption. They used data from air quality measuring stations operated by the Irish Environmental Protection Agency, the Department for Environment, Foodand Rural Affairs, the Scottish Environment Protection Agency, the Finnish Meteorological Institute and the Netherlands NationalInstitute for Public Health and the Environment to determine sulphur dioxide in levels in Ireland, the UK, Finland and the Netherlands during this period.

This simulation suggested that sulphur dioxide from Holuhraun reached areas 3000 miles from the eruption itself, and heights of 4500 m in the atmosphere. The emissions were driven eastwards by a series of anticyclones (expand); in early September an anticyclone moving eastwards from the UK to Scandinavia initially produced northerly winds (i.e. winds from the north) which propelled sulphur dioxide towards Ireland, then westerly winds that drove emissions from Iceland towards northern Finland, later in the month two anticyclones over the North Atlantic and the UK coalesced, forming a ridge of high pressure over the UK which drove emissions through the UK and into the Netherlands.

Schmidt et al. compared these simulation results to data obtained by the OzoneMonitoring Instrument on the Aurora satellite and the InfraredAtmospheric Sounding Interferometer instruments on the MetOp-A and MetOp-B satellites, finding a close comparison between the calculated position of Sulphur Dioxide emissions and the observed positions, with discrepancies occurring on only two days (5 and 21 September).

Comparison of satellite-retrieved and satellite-simulated SO₂ vertical column densities (VCDs) for 5–6 and 20–21 September 2014. For the comparison of the model simulations to the Ozone Monitoring Instrument (OMI) the model output was sampled at OMI overpasses and the column operator was applied, and for the comparison to the Infrared Atmospheric Sounding Interferometer (IASI) the model was sampled at IASI overpasses between 08:00 UTC and 15:00 UTC. Both the OMI and IASI data have been gridded onto the same regular 0.5° by 0.5° longitude-latitude grid as the model simulations. Schmidt et al (2015).

This gave Schmidt et al. the confidence to calculate levels of Sulphur Dioxide based upon the model and satellite observations, coming up with an average figure of 20-60 kilotons per day per day during 6-22 September 2014, rising to 60-120 kilotons per day for the rest of the month. This puts peak emissions slightly higher than twice the peak emissions recorded from the Miyake-jima eruption (54 kilotons per day during December 2000), and suggests that over the course of the eruption Holuhruan may have erupted a total of 11 teragrams of sulphur dioxide (convert to something more sensible), less than the 18 teragrams erupted over the three year period of the Miyake-jima eruption, but more than twice as much as emitted by Miyake-jima during the first six months of that eruption.

The highest concentration of Sulphur Dioxide recorded in Europe during the Holuhruan eruption occurred at Ennis in the Republic of Ireland on 4-8 September 2014, with concentrations reaching a high of ~524 μg/m³ between 5.00 and 6.00 pm on 6 September. This is the first time that sulphur dioxide levels in excess of 400 μg/m³ have been recorded in Europe since 1990, following the introduction of stringent Europe-wide restrictions on industrial emissions in the 1980s. The second highest levels recorded were in Scotland, where average levels of ~320 μg/m³ were recorded on 20-25 September. The highest recorded levels in Finland occurred at Sammaltunturi during the night of 7–8 September, when average sulphur dioxide levels of ~180 μg/m³ were recorded. England and the Netherlands both recorded their highest sulphur dioxide levels on 22 September 2014, with ~96 μg/m³ recorded in England and ~82 μg/m³ recorded in the Netherlands.

Sulphur dioxide pollution is known to cause a wide range of health problems, and the World Health Organisation recommends that exposure to levels higher than 500 μg/m³ be regarded as hazardous, while the Clean Air for Europe Directive mandates that if sulphur dioxide levels remain above 500 μg/m³for more than three hours then a public health warning must be issued. During the 2014-15 Holuhruan eruption recorded sulphur dioxide levels exceeded 500 μg/m³ only once and for only one our at a single monitoring station (Ennis), but concentrations exceeding 350 μg/m³ were recorded for over 100 hours in total at the same station during the course of the eruption, the highest sustained sulphur dioxide concentration recorded in Europe since records began. By contrast on Iceland the Höfn monitoring station, which is only about 100 km from the Holuhruan Lava Field, the highest concentration recorded was 3000 μg/m³, but concentrations exceeding 350 μg/m³ were recorded for only 124 hours in total.

In the United Kingdom sulphur dioxide levels in excess of 266 μg/m³ are considered 'moderate pollution' by the Department for Environment, Food and Rural Affairs. This level was not exceeded at any UK monitoring station during the Holuhruan eruption, but Schmidt et al.'s computer model suggests that this level was exceeded off the northern coast of Scotland for about eleven consecutive hours.

Sulphur dioxide monitoring in Europe began in the 1980s in response to high levels of the gas being produced by industry. Since this time tighter environmental regulations have almost eliminated this source of pollution, and many governments are considering cutting back on monitoring. However the Holuhruan Lava Field eruption has shown that such stations can be useful in monitoring naturally occurring sulphur dioxide emissions, which present the same hazard to health, and the Scottish Environment Protection Agency is now planning to extend sulphur dioxide monitoring in Scotland as a result of this event. Schmidt et al. also recommend that European agencies look to expand satellite monitoring of such emissions, which would allow the better prediction of the movements of clouds of sulphur dioxide, allowing local authorities to plan for pollution events before they occur.

Sunday, 7 September 2014

Magnitude 5.4 Earthquake beneath the Vatnajökull Glacier, Iceland.

The Icelandic Met Office recorded a Magnitude 5.4 Earthquake at a depth of 3.9 km beneath the Vatnajökull Glacier slightly before 7.10 am local time (which is GMT) on Sunday 7 September 2014. This was roughly 4 km to the southeast of the Bárðarbunga Volcano, which has been going through an active period for the last month. Magnitude 5.4 Earthquakes are potentially quite dangerous, but the remote location of this event makes it highly unlikely that there were any casualties or damage.

The approximate location of the 7 September 2014 Vatnajökull Earthquake. Google Maps.

Seismic activity beneath volcanoes can be significant, as they are often caused by the arrival of fresh magma, which may indicate that a volcano is about to undergo an eruptive episode. Bárðarbunga last erupted in about 1862, and has undergone several periods of raised seismic activity since then, most recently in 1996 and 2010, so there is no reason to believe that this weeks events will automatically lead to an eruption from the volcano itself. Bárðarbunga began to undergo seismic activity (Earthquakes) on 19 August, and lava began to erupt from a fissure in the Holuhraun lava field, no the north of the Vatnajökull Glacier, late in the evening of Thursday 28 August, and has continued since then. It is though likely that a magma intrusion has risen through fissures beneath the volcano and now migrated to the lava field.

Lava erupting in the Holuhraun lava field in September 2014. Armann Hoskuldsson/Extreme Iceland.

Iceland lies directly upon the Mid-Atlantic Ridge, a chain of (mostly) submerged volcanoes running the length of the Atlantic Ocean along which the ocean is splitting apart, with new material forming at the fringes of the North American and European Plates beneath the sea (or, in Iceland, above it). The Atlantic is spreading at an average rate of 25 mm per year, with new seafloor being produced along the rift volcanically, i.e. by basaltic magma erupting from below. The ridge itself takes the form of a chain of volcanic mountains running the length of the ocean, fed by the upwelling of magma beneath the diverging plates. In places this produces volcanic activity above the waves, in the Azores, on Iceland and on Jan Mayen Island.

The passage of the Mid-Atlantic Ridge beneath Iceland. NOAA National Geophysical Data Center.

Sunday, 31 August 2014

Eruptions in the Holuhraun lava field.

Lava began to erupt from a fissure in the Holuhraun lava field, no the north of the Vatnajökull Glacier in central Iceland, late in the evening of Thursday 28 August, and has continued to do so for the next three days. The lava field lies to the northeast of Bárðarbunga, a volcano beneath the Vatnajökull Glacier, which began to undergo seismic activity (Earthquakes) on 19 August, and it is though likely that a magma intrusion has risen through fissures beneath the volcano and now migrated to the lava field.

Fresh lava eruptions in the Holuhraun lava field on Friday 29 August 2014. News Hub.

The approximate location of the Holuhraun lava field. Google Maps.