Katla volcano, Iceland: magma composition, dynamics and eruption frequency as recorded by Holocene tephra layers
TL;DR: In this article, a study of the tephra stratigraphy from a composite soil section to the east of the volcano has been undertaken with emphasis on the prehistoric deposits, and the age of individual Katla layers was calculated using soil accumulation rates (SAR) derived from soil thicknesses between 14C-dated marker tephras layers.
Abstract: The Katla volcano in Iceland is characterized by subglacial explosive eruptions of Fe–Ti basalt composition. Although the nature and products of historical Katla eruptions (i.e. over the last 1,100 years) at the volcano is well-documented, the long term evolution of Katla’s volcanic activity and magma production is less well known. A study of the tephra stratigraphy from a composite soil section to the east of the volcano has been undertaken with emphasis on the prehistoric deposits. The section records ∼8,400 years of explosive activity at Katla volcano and includes 208 tephra layers of which 126 samples were analysed for major-element composition. The age of individual Katla layers was calculated using soil accumulation rates (SAR) derived from soil thicknesses between 14C-dated marker tephra layers. Temporal variations in major-element compositions of the basaltic tephra divide the ∼8,400-year record into eight intervals with durations of 510–1,750 years. Concentrations of incompatible elements (e.g. K2O) in individual intervals reveal changes that are characterized as constant, irregular, and increasing. These variations in incompatible elements correlate with changes in other major-element concentrations and suggest that the magmatic evolution of the basalts beneath Katla is primarily controlled by fractional crystallisation. In addition, binary mixing between a basaltic component and a silicic melt is inferred for several tephra layers of intermediate composition. Small to moderate eruptions of silicic tephra (SILK) occur throughout the Holocene. However, these events do not appear to exhibit strong influence on the magmatic evolution of the basalts. Nevertheless, peaks in the frequency of basaltic and silicic eruptions are contemporaneous. The observed pattern of change in tephra composition within individual time intervals suggests different conditions in the plumbing system beneath Katla volcano. At present, the cause of change of the magma plumbing system is not clear, but might be related to eruptions of eight known Holocene lavas around the volcano. Two cycles are observed throughout the Holocene, each involving three stages of plumbing system evolution. A cycle begins with an interval characterized by simple plumbing system, as indicated by uniform major element compositions. This is followed by an interval of sill and dyke system, as depicted by irregular temporal variations in major element compositions. This stage eventually leads to a formation of a magma chamber, represented by an interval with increasing concentrations of incompatible elements with time. The eruption frequency within the cycle increases from the stage of a simple plumbing system to the sill and dyke complex stage and then drops again during magma chamber stage. In accordance with this model, Katla volcano is at present in the first interval (i.e. simple plumbing system) of the third cycle because the activity in historical time has been characterized by uniform magma composition and relatively low eruption frequency.
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TL;DR: Tephrochronology is a unique stratigraphic method for linking, dating, and synchronizing geological, palaeoenvironmental, or archaeological sequences or events as discussed by the authors, which can be used for correlational purposes.
620 citations
Cites background from "Katla volcano, Iceland: magma compo..."
...…and insight into petrogenesis (e.g., Kohn and Topping, 1978; Wilson and Hildreth, 1997; Nakagawa et al., 1999; Smith et al., 2002, 2005, 2006; Óladóttir et al., 2008; Turner et al., 2008b), and for volcanic hazard prediction and risk management (e.g., Shane and Hoverd, 2002; Hurst and Smith,…...
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...As well as providing isochrons for palaeoenvironmental research, tephras provide a comprehensive record or dossier of explosive volcanism and recurrence rates in the Quaternary or earlier and can therefore be used to establish time-space relationships of volcanism and insight into petrogenesis (e.g., Kohn and Topping, 1978; Wilson and Hildreth, 1997; Nakagawa et al., 1999; Smith et al., 2002, 2005, 2006; Óladóttir et al., 2008; Turner et al., 2008b), and for volcanic...
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Journal Article•
TL;DR: In this article, the authors estimate that Icelandic volcanism has produced around 2400 eruptions and about 566±100 km 3 of erupted magma in the last 11 ka, using a postglacial eruption data set.
Abstract: Iceland is one of the most active and productive terrestrialvolcanic regions, with eruption frequency of �20 events per century and magma output rates of�5 km 3 per century Although Iceland is dominated by mafic magmatism and volcanism, as is evident from 91:6:3 dist ribution of mafic, intermediate and silicic erup- tions, its record also features most common terrestrial mag ma types and eruption styles Postglacial volcanism is confined to the neovolcanic zones where 30 active volcanicsystems are responsible for most of the Holocene activity On the basis of our current post-glacial eruptiondata set we estimate that Icelandic volcanism has produced around 2400 eruptions and about 566±100 km 3 of erupted magma in the last 11 ka Effusive activ- ity accounts for�500 eruptions; the remainder is explosive and dictated by su bglacial mafic events (�77%), demonstrating strong environmental influence on eruption s in Iceland In terms of magma output the record is dominated by large volume (>1 km 3 ) effusive mafic eruptions About 50 such eruptions have occu rred throughout postglacial time or�2% of the total number of eruptions However, collectively t hese events pro- duced about 55% of the postglacial magma volume The Eastern Volcanic Zone is responsible for >80% of the eruptions and�60% of the erupted magma volume and has been by far the most pro lific producer among the neovolcanic zones Furthermore, the volume of mafic effu sive eruptions is not evenly distributed through post-glacial time, because only 30% (111 km 3 ) of the total volume was produced in the last 5 ka and the re- maining 70% ( 258 km 3 ) between 5-11 ka However, the production rate per millenni a within these two periods appears to be fairly even, ranging from 20-30 km 3 in <5 ka period and 35-40 km 3 in the 5-10 ka interval The exception is the 10-11 ka interval, when�70 km 3 of mafic lava was formed by the effusive activity or close to double the volume produced per millennia in the period that f ollowed
203 citations
TL;DR: A review of the results of over 25 years of research into tephra horizons in the GRIP, GISP2 and NGRIP cores can be found in this article.
139 citations
TL;DR: Historical developments and significant breakthroughs are presented to chart the revolution in correlation and precision dating over the last 50 years using tephrochronology and cryptotephro chronology.
Abstract: From its Icelandic origins in the study of visible tephra horizons, tephrochronology took a remarkable step in the late 1980 s with the discovery of a ca. 4300-year-old microscopic ash layer in a Scottish peat bog. Since then, the search for these cryptotephra deposits in distal areas has gone from strength to strength. Indeed, a recent discovery demonstrates how a few fine-grained glass shards from an Alaskan eruption have been dispersed more than 7000 km to northern Europe. Instantaneous deposition of geochemically distinct volcanic ash over such large geographical areas gives rise to a powerful correlation tool with considerable potential for addressing a range of scientific questions. A prerequisite of this work is the establishment of regional tephrochronological frameworks that include well-constrained age estimates and robust geochemical signatures for each deposit. With distal sites revealing a complex record of previously unknown volcanic events, frameworks are regularly revised, and it has become apparent that some closely timed eruptions have similar geochemical signatures. The search for unique and robust geochemical fingerprints thus hinges on rigorous analysis by electron microprobe and laser ablation-inductively coupled plasma-mass spectrometry. Historical developments and significant breakthroughs are presented to chart the revolution in correlation and precision dating over the last 50 years using tephrochronology and cryptotephrochronology.
125 citations
Cites background from "Katla volcano, Iceland: magma compo..."
...…building comprehensive frameworks, lattices and catalogues of volcanic events (e.g. Haflidason et al., 2000; Davies et al., 2002; Hall and Pilcher, 2002; Wulf, 2004; Olad ottir et al., 2008; Smith et al., 2011; Zanchetta et al., 2011; Blockley et al., 2012; Wulf et al., 2012; Bourne et al., 2015)....
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TL;DR: The Vedde Ash is the most important volcanic event marker layer for the correlation of Late Quaternary palaeoenvironmental archives in Europe and the North Atlantic as discussed by the authors, and has been traced across much of northern and central Europe, into northwest Russia, within North Atlantic marine sediments and into the Greenland ice cores.
101 citations
Cites background or result from "Katla volcano, Iceland: magma compo..."
...Our data show that the VA was generated by mixing of separate rhyolitic and basaltic magma batches, which is in agreement with previous theories of bimodal volcanism from the Katla volcano (Lacasse et al., 2007; Óladóttir et al., 2008)....
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...Similar mixing processes have been previously postulated for eruptions from Katla system by Lacasse et al. (2007) and Óladóttir et al. (2008)....
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...Basaltic eruptions of Katla are also common (Óladóttir et al., 2008), however the VA represents the only distally detected tephra which contains both the basaltic and rhyolitic phases....
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References
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TL;DR: In this paper, the authors identified 205 eruptions in historical time by detailed mapping and dating of events along with extensive research on documentation of volcanic activity in historical chronicles and classified them into three categories: effusive, effusive and mixed.
571 citations
"Katla volcano, Iceland: magma compo..." refers background in this paper
...Thordarson and Larsen 2006 and references therein)....
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...In historical time, Katla has been the most productive volcanic system in Iceland when volume of magma erupted is considered ( Thordarson and Larsen 2006 )....
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TL;DR: In this paper, the authors report the results of a regional broadband seismic experiment undertaken to determine the three-dimensional velocity structure of the upper mantle beneath Iceland using relative travel times of body waves from teleseismic earthquakes.
Abstract: Oceanic hotspots are generally accepted to be the manifestations of plumes of hot, upwelling mantle material1,2, but the nature of such flows remains enigmatic. Iceland, for example, is one of the most thoroughly investigated hotspots, yet previous seismological3–5 and geodynamic6–12 studies have been unable to constrain the width or temperature of the plume. Here we report the results of a regional broadband seismic experiment undertaken to determine the three-dimensional velocity structure of the upper mantle beneath Iceland using relative travel times of body waves from teleseismic earthquakes. Inversion solutions of the data show a cylindrical zone of low P- and S-wave velocities that extends from 100km to at least 400km depth beneath central Iceland. The radius of the low-velocity anomaly is about 150km, and its magnitude is approximately 2% for P waves and 4% for S waves, indicating that Iceland is underlain by a hot, narrow plume of upwelling mantle.
503 citations
"Katla volcano, Iceland: magma compo..." refers background in this paper
...The elevated volcanic activity in Iceland is due to the superimposition of the North Atlantic ridge system and the Iceland mantle plume (e.g. Vink 1984; Wolfe et al. 1997)....
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TL;DR: In this article, four previously known ash layers (Ash Zones I and II, Saksunarvatn and the Settlement layer) all originating in Iceland have been identified in the Central Greenland ice core GRIP.
496 citations
TL;DR: In this paper, the authors present a model of the triggering of volcanic eruptions based on fractional crystallization and oversaturation of volatile species in a shallow magma chamber and calculate the overpressure in the chamber and consequent increase in its volume by deformation of the surrounding rocks.
452 citations
"Katla volcano, Iceland: magma compo..." refers background in this paper
...the lithostatic pressure; Tait et al. 1989; Gudmundsson 1995)....
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TL;DR: The Skaftar Fires 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).
Abstract: 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.
424 citations
"Katla volcano, Iceland: magma compo..." refers background in this paper
...basaltic tephra layers of the tholeiitic magma suite (e.g. Jakobsson 1979a; Larsen 1984; Thordarson and Self 1993)....
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