Volcanic Eruptions In Iceland Research Articles

Lava shields and fissure eruptions of the Western Volcanic Zone, Iceland: Evidence for magma chambers and crustal interaction

Volcanic eruptions in Iceland occur either from fissures or central vents (lava shields). Within the post-glacial Western Volcanic Zone, the Thjófahraun fissure-fed lava field and Lambahraun lava shield were both erupted ~ 4000 yrs B.P. with eruptive centers separated by only ~ 25 km. Thjófahraun erupted ~ 1 km 3 of pāhoehoe and 'a'ā lava from a 9-km long fissure, whereas the Lambahraun lava shield erupted > 7 km 3 of low effusion-rate pāhoehoe. Thjófahraun lavas contain higher K, Rb, Y and Zr, and lower CaO than Lambahraun lavas at the same MgO, with variations broadly consistent with evolution by low-pressure crystal fractionation. Lambahraun spans a larger range of MgO, which generally decreases over time during the eruption. Lambahraun samples with high Al 2O 3 and low TiO 2 and FeO likely reflect up to 15% plagioclase accumulation. In addition, all samples from Lambahraun exhibit increasing CaO and Nb/Zr with decreasing MgO and overall incompatible-element enrichments greater than predicted by crystal fractionation alone. Although the increase in Nb/Zr and other incompatible elements could be explained by gradually more incompatible-element enriched parental magma being supplied to the magmatic system during the course of the Lambahraun eruption, this process requires very small-scale trace element heterogeneities in the mantle that are apparently decoupled from isotopic variations and a systematic relationship between parental magma composition and extent of differentiation. Alternatively, correlations among incompatible element concentration, increasing differentiation and time during the eruption can be related by concurrent wallrock assimilation and crystallization during melt migration through the crust. Geochemical modeling of assimilation of wallrock clinopyroxene concurrent with crystallization of olivine (± plagioclase) effectively reproduces the observed chemical variations of Lambahraun samples. Similar chemical characteristics exist in several other Western Volcanic Zone lava shields but not in fissure eruptions. Magmas that fed fissure eruptions may also have been modified by interaction with the crust prior to aggregation in crustal magma chambers, but the geochemical signature of this process is obscured by magma mixing. In contrast, Icelandic lava shields that preserve deeper level processes may not have developed shallow magma chambers; rather they probably represent slow effusion from magma systems that are continually being recharged and reacting with the crust during the course of their eruptions.

Halving of the northern wetland CH4 source by a large Icelandic volcanic eruption

Northern temperate and high‐latitude wetlands are a major source of the greenhouse gas methane (CH4). Here, we estimate the sensitivity in the strength of this source to the effects of large Icelandic volcanic eruptions such as the Laki eruption of 1783–1784. We applied spatially explicit modeled sulfate aerosol and S deposition fields from a Laki eruption simulation to a climate‐sensitive model of CH4 emissions from wetlands. We estimate that the combined influence on climate and S deposition from the Laki eruption halved the output of CH4 from wetlands north of 30°N for the first 12 months following the eruption. The largest short‐term component responsible for the CH4 suppression is the aerosol‐influenced surface cooling, although the effect of large‐scale S deposition on CH4 emissions provides a longer‐term suppressive effect on emissions. Together, we estimate this combination of processes to result in an annual suppression of ∼20 Tg CH4 in the year of the eruption and two subsequent years. Further, the impact of the eruption on atmospheric CH4 concentration extends beyond the likely duration of suppressed emission. The modeled effect of this large Icelandic eruption is consistent with ice core records of atmospheric CH4 concentrations at the time and is equivalent, in size, to the current estimated suppressive effect of industrially derived S pollution on the global wetland CH4 source.

Optically stimulated luminescence (OSL) dating of coastal aeolian sand accumulation in Sanday, Orkney Islands, Scotland

Optically stimulated luminescence (OSL) dating of sand has been used to identify periods of enhanced aeolian activity at two coastal archaeological sites in Orkney that coincide with periods of Holocene climatic deterioration recorded elsewhere in both Scotland and W Europe. Areas of Tofts Ness, Sanday were settled from the Neolithic, abandoned in the late Neolithic/early Bronze Age, reoccupied and permanently abandoned in the Iron Age. Sand layers above the Neolithic soils have been OSL dated to about 4000 BP, correlating well with a period of increased aeolian activity elsewhere in W Europe. OSL dating of aeolian sands above midden deposits and a Bronze Age burial at Lopness on Sanday suggest dune development by 3000 BP, although both sites also contain sand that was deposited during the `Little Ice Age'. Several possible mechanisms may have contributed to an increase in aeolian activity during the Holocene that led to the abandonment of these sites. Although volcanic eruptions in Iceland cannot be discounted as a contributory factor, a more likely driver of change in sand dune systems is the enhanced N Atlantic storminess suggested by ice core records from Greenland. During periods of climatic deterioration the declining productivity of other agricultural land places enhanced demands on agriculturally marginal sand dunes, leading to further destabilization and the potential for enhanced sand transport events.

Long‐term suppression of wetland methane flux following a pulse of simulated acid rain

Wetlands are a potent source of the radiatively important gas methane (CH4). Recent findings have demonstrated that sulfate (SO42−) deposition via acid rain suppresses CH4 emissions by stimulating competitive exclusion of methanogens by sulfate‐reducing microbial populations. Here we report data from a field experiment showing that a finite pulse of simulated acid rain SO42− deposition, as would be expected from a large Icelandic volcanic eruption, continues to suppress CH4 emissions from wetlands long after the pollution event has ceased. Our analysis of the stoichiometries suggests that 5 years is a minimum CH4 emission recovery period, with 10 years being a reasonable upper limit. Our findings highlight the long‐term impact of acid rain on biospheric output of CH4 which, for discrete polluting events such as volcanic eruptions, outlives the relatively short‐term SO42− aerosol radiative cooling effect.

Towards a Holocene tephrochronology for Sweden: geochemistry and correlation with the North Atlantic tephra stratigraphy

AbstractNorthern Europe has been affected by fallout of tephra from volcanic eruptions in Iceland throughout at least the Late‐glacial and Holocene. Microscopic volcanic ash horizons found in the British Isles, northern Germany and Scandinavia (e.g. Hekla 4) now provide important regional isochrons. Over recent years analytical techniques such as electron probe microanalysis (EPMA) have helped identify these distal tephra layers by glass geochemistry. Early tephra work in Sweden used refractive indices and bracketing radiocarbon dates for identification, resulting in tentative correlation. This paper presents geochemical data for Icelandic Holocene tephra in Sweden. Several sites in central Sweden have four distinct mid‐Holocene tephra layers. Correlation with the Icelandic record indicates that the following tephra layers are present: Hekla 4 (ca. 3830 yr BP), Kebister tephra (ca. 3600 yr BP), Hekla 3 (ca. 2880 yr BP) and Askja ad 1875. Preliminary analyses suggest that more, previously unidentified, tephra layers are present in low concentrations in the region, indicating potential for expanding the Swedish tephrochronology for palaeoecological and palaeoenvironmental work in northern Europe. Copyright © 2004 John Wiley & Sons, Ltd.

A four-year study of shear-wave splitting in Iceland: 2. Temporal changes before earthquakes and volcanic eruptions

Abstract This chapter reports temporal variations in the time-delays between split shear-waves before both earthquakes and volcanic eruptions in Iceland. The hypothesis is that during a build-up of stress, crack distributions in a large volume surrounding the immediate source zone are modified until the level of cracking reaches fracture criticality, when shear strength is lost, rocks fracture, and earthquakes, or some types of eruptions occur. In one two-year period, when volcanic and magmatic activity appeared to be low, changes in shear-wave splitting in SW Iceland were observed routinely before earthquakes with magnitudes between M 3.5 and M 5.1. Assuming a linear relationship between earthquake magnitude and the rate of increasing crack aspect-ratio in this comparatively narrow amplitude range, the time and magnitude of a M 5 earthquake was successfully stress-forecast. These results confirm a new understanding of pre-fracturing deformation of in situ rock that has implications over a wide range of situations where the crust undergoes changes at low levels of deformation below those at which rocks fracture. Potential applications of this new understanding include monitoring hydrocarbon production, as well as stress-forecasting earthquakes and some volcanic eruptions.

Study of volcano/ice interactions gains momentum

Observations of recent volcanic eruptions in Iceland and detailed studies of sub‐glacially erupted deposits and the interaction of lava and pyroclastic flows with snow and ice have provided important new data that should lead to significant advances in the understanding of volcano/ice interaction on Earth and Mars. A conference on this subject, the first of its kind, recently brought together geologists, geophysicists, glaciologists, and planetary scientists studying various aspects of volcano‐ice interaction.

Comment on “Satellite radar images capture a subglacial volcanic eruption in Iceland”] Comment: Subglacial eruptions and synthetic aperture radar images

In a news piece published in the May 4, 1999, issue of Eos,Garvin et al. present RADARSAT satellite synthetic aperture radar (SAR) images of the subglacial volcanic eruption in the Gnmsvotn caldera within the Vatnajokull ice cap, Iceland, that occurred December 18–28, 1998. As pointed out in this piece, the images show considerable changes in surface backscatter of the radar signal within the caldera during and after the eruption. The authors suggest that the dark patches with an area of approximately 4 km2, observed within Grímsvötn, are open water. On the basis of the size of the dark patches, Garvin et al. estimate the volume of ice melted to have been about 1 km3 and the energy provided for melting, E = 3 × 1017 J, to have been about 30% of that of the 1996 Gjalp eruption, which occurred 12 km north of the 1998 eruption site [Gudmundsson et al., 1997]. Our groundbased and aerial observations at Gnmsvotn, however,show that this estimate of melting and energy release is far too high.

Endemic stress, farming communities and the influence of Icelandic volcanic eruptions in the Scottish Highlands

Abstract This paper explores present understanding of the possible impacts that volcanic eruptions in Iceland might have had upon the environments and traditional farming systems of the Highlands and Islands of Scotland, before ‘the Clearances’ of the late 18th and 19th centuries AD . It reconstructs both the nature of the impacts and the character of the risks that might have been faced by subsistence communities within the historical period from such Icelandic volcanic eruptions, and as such serves to redirect a research emphasis that has previously been principally focused upon the European Bronze Age. The study also emphasizes that it is inadequate to envisage the impacts from volcanic aerosols as threats to the community to be understood solely along a continuum of environmental hazards. For example, in the historical period before the Clearances, the wider social, political and economic contexts of subsistence economies affected can be shown to have raised or lowered the thresholds at which environmental risks became real or were turned into subsistence crises. In times past, as now, the capacity of people to cope with such environmental vicissitudes would have varied according to a complex of pre-disposing factors, their recent experiences, attitudes and perceptions, political and social relationships, health and well-being (especially their susceptibility to respiratory problems), economy, education and memory, and general inventiveness and resilience. Unlike much earlier research, which focused upon the European Late Bronze Age and emphasized global climatic change and its regional-scale consequences, this account of more recent times emphasizes the small scale, the importance of local pre-disposition and contingency, and hence the likely patchiness and indeterminacy of consequences on the ground of distant volcanic eruptions. The paper concludes that in the historical past, for a variety of environmental, agricultural, social and political reasons, some communities in the Highlands and Islands would have already been typically at risk of a subsistence crisis one year in every four or five. Hence a particular group of people could have been at notable further risk if a significant quantity of volcanically derived noxious and toxic materials had fallen upon them. As a result, for both habitats and human populations in historical times, the consequences of an Icelandic volcanic eruption are likely to have varied from place to place and from time to time. This analysis also suggests that it is difficult to envisage that any postulated region-wide abandonment of settlement in the British Isles might be attributable, directly or indirectly, to the distal impacts of volcanic eruptions in Iceland.

Satellite radar images capture a subglacial volcanic eruption in Iceland

What are believed to be the first satellite synthetic aperture radar (SAR) images of a sub‐glacial eruption have been captured by the Canadian Space Agency's RADARSAT at the Grimsvotn volcano in Iceland. The high‐resolution images were made in late November 1998 before the eruption, in late December 1998 during the eruption, and in mid‐January 1999 after the eruption (Figure 1), all in spite of persistent cloud cover and darkness.The subglacial eruption, centered within Grimsvotn volcano, occurred between December 18 and 28, 1998. It began at the southern rim of the caldera, in the west‐central region of the Vatnajokull ice cap glacier, the largest in Europe with a total area of ∼8300 km2. During the eruption's early stages, five craters were active along an eruptive fissure, extending east‐west along the southern caldera rim.

A Scottish speleothem record of the H-3 eruption or human impact? A comment on Baker, Smart, Barnes, Edwards and Farrant

Studies of a stalagmite sample from Sutherland, Scotland, have identified a period of enhanced growth that lasted for four years and has been dated to 1135 ± 130 BC (Baker et al., 1995). This episode is unique within this sample and has not been observed elsewhere. The authors correlate it with the Icelandic volcanic eruption at 1021 + 130/-100 Bc that produced the Hekla-3 (H-3) tephra. There is, however, no direct evidence for a causal relationship between volcanic activity in general, or the H-3 eruption in particular, and the growth patterns of the stalagmite. As an alternative to the volcanic explanation of enhanced growth, we suggest that the speleothem could reflect environmental changes associated with woodland decline and the spread of blanket peat.

Volcanoes and peat bogs

Peat bogs in the British Isles contain tephra from volcanic eruptions in Iceland; tephra in the Falkland Islands most likely derives from Andean volcanoes. Study of these far‐travelled volcanic products is making a significant contribution to our understanding of past environmental changes.

Modelling the impact of Icelandic volcanic eruptions upon the prehistoric societies and environment of northern and western Britain

Abstract Many studies now address the impact of Icelandic volcanic eruptions upon the societies and environment of Britain and Ireland. It has become apparent that the assumptions of the magnitude of volcanic impact inherent in these studies are open to question. The scale of climatic change following many eruptions has been observed to be ephemeral or non-existent, whilst the impact of toxic volatile gases and aerosols is dependent, to a large degree, on the vulnerability of the receptor rather than the scale of deposition. The scale and extent of volcanic climatic-forcing mechanisms are examined and the popular perception of the effectiveness of these is challenged. In particular, the concepts of harsh volcanic winters and cool volcanic summers is examined via case studies of the impacts of the three largest eruptions of recent and historical times, i.e. those of the Laki fissure, Tambora and Mount Pinatubo. Alternative volcanic forcing mechanisms for environmental change are considered, principally those concerned with the transport and deposition of toxic volatile material. The need for caution in the adoption of these models is also urged. It is suggested that workers in this field need to adopt a clearer theoretical framework when contemplating the association of palaeoenvironmental data and volcanic events. Such a framework is proposed.

An Amazing and Portentous Summer: Environmental and Social Responses in Britain to the 1783 Eruption of an Iceland Volcano

This paper investigates the impact of the 1783 eruption of the Laki volcanic fissure in Iceland. This was the most violent, extensive and prolonged volcanic episode which has occurred in the northern hemisphere during the modern era. A detailed examination of newspaper accounts and other documentary evidence reveals the dramatic effect of the eruption on the weather over much of Western Europe. It is shown that Icelandic volcanic eruptions can cause serious environmental damage and extreme climatic disturbance in locations far from the source. Moreover, the evidence indicates a variety of human responses to the weather conditions ranging from panic to attempts to find a scientific explanation.

Dates of Holocene Icelandic volcanic eruptions from tephra layers in Irish peats

Tephra from historic and prehistoric eruptions of Oraefajøkull and Hekla, Iceland, have been found in Irish peats. Using a series of stratigraphically related high-precision radiocarbon measure ments, the date of a known-age eruption has been satisfactorily estimated. Based on the same techniques, the calendrical date of the Hekla 4 eruption has been estimated as 2310 ± 20 BC.

Acid-loading from Icelandic Tephra Falling on Acidified Ecosystems as a Key to Understanding Archaeological and Environmental Stress in Northern and Western Britain

This paper proposes that the additional acid-loading brought about by the deposition of large quantities of acid aerosols from Icelandic volcanic eruptions may be responsible for environmental stress and settlement abandonment postulated by previous authors for northern and western Britain in the late 2nd millennium BC. The mechanism is predicted to have been of significance only in those ecosystems that were already significantly acidified. The paper discusses and counters suggestions that the volcanically-induced climatic change was the principal mechanism for both an apparent abandonment of settlement over large areas of northern Scotland, and the stress experienced by oak trees growing on raised bogs in Ireland.

Did Icelandic volcanic eruptions influence the post-glacial vegetational history of the British Isles?

Did Icelandic volcanic eruptions influence the post-glacial vegetational history of the British Isles?

Non-climatic factors and the environmental impact of volcanic volatiles: implications of the Laki fissure eruption of AD 1783

Studies of the potential of Icelandic volcanic eruptions to modify the environment of the British Isles have primarily concentrated on the degree of induced climate change, but models and temperature records suggest that the scale of such change may have been minimal. As a result it is difficult to account for change in the palaeoenvironmental and archaeological records, in response to a volcanic eruption, by invoking climate change alone. An additional mechanism is proposed by which Icelandic volcanic eruptions transport and deposit environmentally-significant levels of acid volatiles and halogens. Contemporary documentary evidence indicates a widespread dry, smoky haze throughout western Europe during the Laki fissure eruption in the summer of AD 1783, indicative of the presence of volcanically generated gases in the lower atmosphere. Severe damage to crops and trees occurred in a number of locations in Britain and western Europe, the descriptions of which are consistent with the impact of acid deposition. It is suggested that the deposition of acids and halogens emitted in Icelandic volcanic eruptions may be more significant than climatic perturbations for ecosystems in the British Isles.

Chemistry of gases associated with geothermal activity and volcanism in Iceland: A review

The concentrations of CO2, H2S, and H2 in geothermal reservoir fluids in Iceland are fixed by equilibria with alteration minerals. CH4 concentrations are typically very low, and gas‐gas equilibria involving CO2, H2, and CH4 are generally not closely approached. In some geothermal systems the N2 is atmospheric only, but a magmatic N2 contribution is significant in others. N2/Ar ratios lie mostly between that of the atmosphere (85) and the N2/Ar ratio in cold water in contact with the atmosphere (37). Fluids with a strong magmatic N2 contribution have N2/Ar ratios of 40–60. During several volcanic eruptions in Iceland, magmatic gases have emerged at the surface beyond the eruptive vents and mixed with surrounding groundwaters. CO and H2 can be detected closest to the vent, but only CO2 is detected at greater distances. During the present volcanic episode at Krafla, fugitive constituents have been transported into the geothermal reservoir from the underlying magma chamber. Probably most of the carbon and sulphur in altered rocks of high‐temperature geothermal systems have been derived from degassing magma bodies.

Greetings from Iceland

ABSTRACTA brief account of ash-falls and aerosols fron historical volcanic eruptions in Iceland that have affected Scandinavia is given with special reference to the noxiou effects of aerosols from...