Grimsvotn Research Articles

Atmospheric Aerosol Loading and Transport Due to the 1783-84 Laki Eruption in Iceland, Interpreted from Ash Particles and Acidity in the GISP2 Ice Core

Glass shards from the A.D. 1783 Laki fissure eruption in Iceland have been identified in the GISP2 ice core from Summit, Greenland, at a level just preceding the major acidity/sulfate peak. Detailed reconstruction of ice stratigraphy, coupled with analyses of solid particles from filtered samples, indicate that a small amount of Laki ash was carried via atmospheric transport to Greenland in the summer of 1783, whereas the main aerosol precipitation occurred in the summer and early fall of 1784. Sulfate concentrations in the ice increase slightly during late summer and fall of 1783 and remain steady throughout the winter due to slow oxidation rates during this season in the Arctic. The sulfate concentration rises dramatically in the spring and summer of 1784, producing a massive sulfate peak, previously believed to have accumulated during the summer of 1783 and commonly used as the marker horizon in Greenland ice core studies. The chronology of ash and acid fallout at the GISP2 site suggests that a significant portion of the Laid eruption plume penetrated the tropopause and that aerosol generated from it remained aloft for at least 1 yr after the eruption. Based on comparisons with other glaciochemical seasonal indicators, abnormally cool conditions prevailed at Summit during the summer of 1784. This further supports the claim that a significant volume of sulfate aerosol remained in the Arctic middle atmosphere well after the eruption had ceased.

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?

Ejection of Trace Metals from Volcanoes

Investigation of trace element content of snow which fell through the pyroclastic ejecta of the Hekla, Iceland eruption of 1991 revealed elevated concen t ra t ions o f a var iety o f elements. Laboratory rinses of pristine tephra and lava show similar concentrations as the snow when the water/rock ratio is 12.5. Many metals have concentrations higher than 100 ppb (Ti, Mn, Fe), between 10-100 ppb (Cu, Zn), and between 1-10 ppb (So, V, Cr, Co, As, Se, Sn, La, Sm) in the snow and tephra rinses. The light REE (LREE), that have the highest chondritic abundances, contain greatest values in the snow. The metals depict a positive correlation with CI-. No REE fractionation occurs during volatilization from the magma. It is proposed here that the metals are evaporated as chlorides during devolatilization of the magma in the eruption cloud. The metals form solid sublimates on the surface of the tephra and lava upon cooling. These halides are very soluble and are dissolved upon contact with the first rain that falls on the erupted solids.

The Laki (Skaft�r Fires) and Gr�msv�tn eruptions in 1783?1785

The Laki (Skaftar Fires) fissure eruption in southern Iceland lasted for eight months during 1783 to 1784, and produced one of the largest basaltic lava flows in historic times (14.7±1.0 km3). In addition, neighboring Grimsvotn central volcano was frequently active during the period from May 1783 to May 1785. The combined activity is interpreted as having been the result of a two-year-long volcano-tectonic episode on the Grimsvotn volcanic system. Contemporary descriptions of the explosive activity make it possible to relate the tephra stratigraphy to the progress of the eruption on a weekly basis and show that activity on the fissures propagated to the NE with time, towards Grimsvotn. The eruption at Laki began on 8 June with a brief explosive event on a short fissure, and lava rapidly began to flow into the Skafta river gorge. It reached the lowlands, 35 km away, four days later and continued to flow, with variable discharge, until 7 February 1784. Approximately 90% of the lava was emplaced in the first five months of activity. The 27-km-long vent complex is composed of tenen echelon fissures distributed on both sides of the much older Laki hyaloclastite mountain. The surface expression of each fissure is a continuous row of vents consisting of scoria cones, spatter cones, and tuff cones. Six tephra fall units are positively identified; two units are completely compsed of phreatomagmatic tephra derived from two tuff cones and the others are Strombolian deposits. The volume of tephra, including ash fall that extended to mainland Europe, is 0.4 km3 dense rock equivalent volume, or 2.6% of the total erupted volume. Interpretation of contemporary descriptions of tephra falls, combined with the preserved stratigraphy, allow the identification of ten eruptive episodes during the eight months of activity on the Laki fissures. These eruptive episodes are inferred to have resulted from the unsteady flow of magma in the feeder system. In addition, at least eight eruption episodes occurred at Grimsvotn in 1783 to 1785, five in 1783, two in 1784, and one in 1785. Each episode at Laki began with a seismic swarm of increasing intensity that led to the formation of a new fissure, the opening of which was followed by short-lived phreatomagmatic activity caused by the high water table around the eruption site. Activity usually changed to violent Strombolian or sub-Plinian, followed by Hawaiian fire fountaining and effusive activity as the availability of groundwater dwindled. Thus, the explosive activity associated with the opening of each fissure was largely controlled by external watermagma interactions. Maximum effusion rates, occurring in the first two episodes, are estimated to have been 8.5x103 and 8.7x103 m3 s-1 from fissures totaling 2.2 and 2.8 km in length, respectively, and, in general, discharge gradually decreased over time. The highest rates are equivalent to 5.6x103 and 4.5x103 kg s-1 per meter length of fissure, values that could conceivably be similar to those that produced some flood basalt lava flows. Maximum fire fountain heights are estimated to have varied from 800 m to 1400 m and convecting eruption columns above the vents rose to a maximum altitude of about 15 km. The release of sulfur gases during fountaining produced an acid haze (aerosol) which spread widely and had a considerable environmental, and possibly climatic, impact on the Northern Hemisphere.

Population, agriculture, and famine: Iceland, 1784–1785

Studies of past famines are useful as portrayals of a society under stress and valuable as testing grounds for ideas on the causes and consequences of famine. Older historical sources may lack some of the richness and detail available to students of modern famines, but history offers hindsight and valuable opportunities to integrate famine studies with long-term views of a society and its ecology. This paper takes a different tack from many economic histories of past famines, especially those that rely heavily on economic measures of ecological sufficiency, such as the prices of wheat, labor, and land. It describes the effects of the disastrous 1783 eruption of Iceland's Lakagigar (Laki craters) on a largely subsistent population for whom relief measures were belated and few. At the time of the disaster the entire population lived in households whose main livelihood consisted of farming or fishing. Both these activities were acutely disrupted by the eruption. In this paper, the course of the famine and its effects on population will be analyzed and reviewed in the light of long-term trends in Icelandic population and food production.

The 1783 Lakagigar eruption in Iceland: geochemistry, CO2 and sulfur degassing

About 12.3 km3 of basaltic magma were erupted from the Lakagigar fissure in Iceland in 1783, which may have been derived from the high-level reservoir of Grimsvotn central volcano, by lateral flow within the rifted crust. We have studied the petrology of quenched, glassy tephra from sections through pyroclastic cones along the fissure. The chemical composition of matrix glass of the 1783 tephra is heterogeneous and ranges from olivine tholeiite to Fe−Ti rich basalt, but the most common magma erupted is quartz tholeiite (Mg#43.6 to 37.2). The tephra are characterized by low crystal content (5 to 9 vol%). Glass inclusions trapped in plagioclase and Fo86 to Fo75 olivine phenocrysts show a large range of compositions, from primitive olivine tholeiite (Mg#64.3), quartz tholeiite (Mg#43–37), to Fe−Ti basalts (Mg#33.5) which represent the most differentiated liquids and are trapped as rare melt inclusions in clinopyroxene. Both matrix glass and melt inclusion data indicate a chemically heterogeneous magma reservoir, with quartz tholeiite dominant. LREE-depleted olivine-tholeiite melt-inclusions in Mg-rich olivine and anorthitic-plagioclase phenocrysts may represent primitive magma batches ascending into the reservoir at the time of the eruption. Vesicularity of matrix glasses correlates with differentiation, ranging from 10 to 60 vol.% in evolved quartz-tholeiite glasses, whereas olivine-tholeiite glasses contain less than 10 vol.% vesicles. FTIR analyses of olivine-tholeiite melt-inclusions indicate concentrations of 0.47 wt% H2O and 430 to 510 ppm for CO2. Chlorine in glass inclusions and matrix glasses increases from 50 ppm in primitive tholeiite to 230 ppm in Fe−Ti basalts, without clear evidence of degassing. Melt inclusion analyses show that sulfur varies from 915 ppm to 1970 ppm, as total FeO* increases from 9 to 13.5 wt%. Sulfur degassing correlates both with vesicularity and magma composition. Thus sulfur in matrix glasses decreases from 1490 ppm to 500 ppm, as Mg # decreases from 47 to 37 and vesicularity of the magma strongly increases. These results indicate loss of at least 75% of sulfur during the eruption. The correlation of low sulfur content in matrix glasses with high vesicularity is regarded as evidence of the control of a major exsolving volatile phase on the degassing efficiency of the magma. Our model is consistent a quasi-permanent CO2 flux through the shallow-level magmatic reservoir of Grimsvotn. Following magma withdrawal from the reservoir and during eruption from the Lakagigar fissure, sulfur degassing was controlled by inherent CO2-induced vesicularity of the magma.

Sedimentology, Paleoflow Dynamics and Flood History of JoKulhlaup Deposits: Paleohydrology of Holocene Sediment Sequences in Southern Iceland Sandur Deposits

ABSTRACT This paper examines the sedimentology of a series of deposits associated with catastrophic floods caused by subglacial volcanic eruptions in southern Iceland. A simple model is proposed for the interpretation of the sediments in terms of changes in flow characteristics of the fluid-sediment mix. A range of sediment types characteristic of these flood flows is identified, the predominant one being thick, massive, homogeneous, poorly structured, black pumice, fine gravels, with 65 p rcent silt + clay (Type E); and single lithology boulder deposits (Type F). These flood deposits alternate with, or are channeled into, more 'normal' sandur deposits, comprising heterogeneous, poorly sorted, clast-supported, imbricated, rounded cobble and pebble gravels (Type G). The dominant sediment sequences are interpreted as representing hyperconcentrated fluid-sediment mixtures, with dispersive stresses acting to create massive, poorly sorted, nongraded or inversely graded sediments, the latter characterized by large surface boulders. The vertical changes in sediment type reflect significant changes in flow conditions during transport and subsequent deposition, with an initial massive flood surge followed by flow deceleration, sediment 'freezing' and dewatering, producing a more fluid series of flows. The more fluid phases were associated with extensive erosion and channelization, cutting deep scour channels marked by residual streamlined hummocks, boulder lags, and fields of 'megaripples', leading downstream to a 'washed' sandur plain. The paper examines some of the problems associated with the application of paleoflow models for determining former flow dynamics. The models adopted suggest that most of the flows occurred as relatively mobile, low viscosity flows, with little internal resistance to shear. While sediment concentrations are estimated to have reached about 50 percent by weight, with maximum yield strengths between 2.9 103 and 4.2 105 dn cm -2, maximum viscosities ranged between only about 2 and 8 102 poises. A range of paleovelocity models applied to the flood sediment indicates flow rates of between abo t 4 and 13 ms-1, with peak discharges reaching a maximum of 3.3 105 m3 s -1. Dating of the deposits by 14C dating and tephrochronology indicates that at least 8 major sediment-producing jokulhlaups occurred over a 4,000-year period, between c 4500 yr BP and 1357 AD. Hence, although relatively rare, the effects of these floods still dominate the proglacial landscape, probably producing > 85 percent of the total thickness of proglacial sandur sediments.

Lateral magma flow, caldera collapse, and a mechanism of large eruptions in Iceland

Lateral magma flow from shallow magma chambers, and associated caldera collapse, has frequently been invoked as a mechanism of fissure eruptions in Iceland. This mechanism is examined from the point of view of fluid dynamics and rock mechanics. It is found that if the magma from a shallow chamber is to flow laterally rather than vertically towards the surface, the density of the roof of the chamber must be much less than the density of the magma, and also less than the density of the crust along the pathway of the resulting dike. It is concluded that formation or reopening of caldera fractures has no effect on the magmatic pressure in the chamber and thus does not lead to magma being squeezed out of it. It is also found that most shallow magma chambers in Iceland are too small to give rise to large fissure eruptions of the order of several km 3. A different mechanism is proposed, of which the salient features are the following. Large eruptions are fed by partially molten magma reservoirs, with an average magma fraction of 0.25, located at the boundary of the crust and upper mantle, at depths of 8–10 km beneath the volcanic zones. If the magmatic pressure in a reservoir increases, the crustal layers above may bend slightly and thereby develop high compressive stresses. For a while, the reservoir may thus contain magma with excess pressure much greater than the tensile strength of the crust. Subsequently, when an eruption occurs, the eruptive volume may be abnormally large compared with the reservoir volume. It is estimated that the ratio of reservoir volume to eruptive volume may then be as little as about 200, compared with an ordinary ratio of about 5000. This mechanism is applied to the Lakagigar eruption of 1783, which lasted about 8 months and produced some 12 km 3 of lava. It is concluded that, if this eruption was fed by the Grimsvötn reservoir, only the uppermost few km of that reservoir supplied magma during the eruption.

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.

Magnetic and thermal effects of dike intrusions in Iceland

Oriented core samples were collected from 18 lava‐dike contacts in Iceland, in locations of low to moderate (<100°C) regional hydrothermal alteration. Alternating field demagnetization of these samples shows that they generally carry a strong and stable remanence. Magnetic directions in the lavas follow a simple pattern, demonstrating that the remanence of the contact zone has only been reset within very short distances from the contact surface. On average, this distance may be only one tenth of the thickness of a typical dike (4 m). Other magnetic properties (remanence intensity, susceptibility, Curie point) of the contact zone are affected to a lesser or a less regular degree than the remanence direction. It is concluded that for the crustal depth of this study, thermal conduction models do not apply to temperature anomalies set up by dike intrusions or fissure eruptions in Iceland, presumably because of rapid advection of groundwater into the active fissures. These results also indicate that the magnetic anomalies observed over Iceland are only to a small extent caused by dikes.

Surface Temperature Changes Following the Six Major Volcanic Episodes between 1780 and 1980

Abstract Examined is the effect on surface temperature of the volcanic eruptions of Asama and Laki in 1783, Tambora in 1815, Coseguina in 1835, Krakatoa in 1883, Santa Maria, Soufriere and Pelee in 1902, and Agung in 1963, using temperature records extending back to 1781. These records include New Haven, Connecticut, in North America; Edinburgh, De Bilt, Copenhagen, Berlin and Vilnius in Northern Europe; Geneva, Basel, Hohen-peissenberg, Vienna and Budapest in Central Europe; the “Central England” data of Manley; and the merged Northern Hemisphere data of Groveman and Landsberg and Jones et al. At New Haven and in Europe there is more evidence of a cooling following eruptions in subtropical and temperate latitudes than in equatorial latitudes (despite the similarity in mean dust-veil index), with a cooling most evident following the Asama and Laki eruptions in Japan and Iceland, and next most evident following the Coseguina eruption in Nicaragua. Following the tremendous Tambora eruption, the eruption wit...

The Great Tolbachik Fissure Eruption: Geological and Geophysical Data 1975–1976

In this decade, the devastating eruptions of Mount St. Helens in May 1980 and of El Chichón (Mexico) in March–April 1982, along with recurring signs of possible precursory activity at Long Valley caldera (California), have greatly increased public as well as scientific awareness of volcanic phenomena. Yet, even though the Great Tolbachik Fissure Eruption (GTFE) in 1975–1976 was larger than any in the world thus far in the 1980s, it received scant notice outside the USSR because of its remote location in the Kamchatka Peninsula (off limits to westerners) and because initial reports of it were almost exclusively in Russian. This new book, edited by Fedotov and Markhinin, now makes available to the western world information regarding the GTFE, the biggest volcanic event in the 1970s. Moreover, it was the largest basalt eruption in the Kurile‐Kamchatka arc in recorded history and, on a global basis, the most voluminous outpouring of basalt since the 1783 Laki fissure eruption in Iceland.

Report on Grimsvotn (Iceland)

Report on Grimsvotn (Iceland)

Report on Grimsvotn (Iceland)

Report on Grimsvotn (Iceland)

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...

Icelandic Subglacial Volcanism: Thermal and Physical Studies

The dominant products of subglacial volcanic eruptions in Iceland are pillow basalt and sideromelane tuff. Physical and thermal studies of these materials indicate that rapid heat transfer from magma to ice takes place during the eruption. Heat from the cooling magma is more than sufficient to melt the volume of ice displaced by the growing volcanic pile. The mechanism by which the eruption switches from effusive (pillow basalt) to explosive (tuff) involves magma vesiculation combined with rapid chilling by meltwater. The transition is somewhat pressure dependent, generally occurring at water depths of 100-200 meters.

Generation of Icelandic rhyolites by melting of plagiogranites in the oceanic layer

Trondhjemite and quartz diorite xenoliths ejected in recent Icelandic eruptions are believed to be derived from plagiogranites within layer 3, formed by fractional crystallisation of basaltic magmas in the lower crust. Evidence indicates that rift jumping to older crust can lead to partial melting of plagiogranites at depth and their eruption as rhyolitic magmas.

Chlorine in basalts from Iceland

Chlorine has a higher solubility in basaltic magmas than other volatiles. A theoretical degassing model predicts that less than 10% of the chlorine originally present in the magma is lost to the atmosphere during surface degassing. This prediction is born out by strong correlation between chlorine and nonvolatile elements in samples from recent volcanic eruptions in Iceland. It is concluded that the chlorine content of subaerial basaltic lavas is proportional to the chlorine content of the magmas. Assuming a roughly constant ratio between chlorine and water in the magmatic gas phase and assuming further that this ratio approximates the Cl H 2O ratio in sea water and sediments it is possible to assign each basaltic magma a fixed amount of water. The figures thus obtained (0.3–1.2% H 2O) are identical with previously assumed water contents of basaltic magmas. The implied water contents of the melts are discussed in terms of derivation from hydrous mantle phases. It is concluded that such phases can supply only a fraction of the assumed water content, the rest is derived from an additional volatile source in the mantle. The mantle source giving rise to alkali basalts in Iceland has a lower content of volatiles than the tholeiite source.

Glacial advance relative to volcanic activity since 1500 AD

THERE may be a connection between the periodicity of glacial advance and the occurrence of volcanic eruptions. Lamb1 has presented a graph which shows a similar curve for Arctic sea ice off Iceland and great Icelandic volcanic eruptions since 870 AD and Bray2 found the number of maximum advances of alpine glaciers since 1680 AD is significantly related (χ2 = 7.8, P < 0.01) to intervals with a volcanic dust veil index of 1,000 or greater. The volcanic dust estimates have now been extended to 1500 AD (ref. 1) and in this paper I analyse the relationship between these estimates and records of maximum glacial advance from 1500 AD to the present.

Distance Measurements across the Heimaey Eruptive Fissure

IN describing the latest Icelandic eruption, Kirkjufell, Thorarinsson et al.1 showed how it began as an erupting fissure about 1,600 m long and how activity ceased on all but the central three vents after 3 d. We have made precise distance measure ments between four fixed stations located around the southern end of the fissure (Fig. 1) on two visits in February and April. The measurements, made with the National Physical Laboratory Mekometer III prototype2,3, corrected for atmospheric refractive index and modulating frequency, are shown plotted with their expected errors against time in days after January 23 on Fig. 3. Also shown on Fig. 3 are the curves of the form d=d0(1–exp(aT)) where d is the strain at time T, d0 is the strain at time zero and a is the inverse of a time constant, which best fit the observed results. Each best fit has the same time constant, 7.5 d, and is in good agreement with the observations, excepting the April result of line 3–1A.