Magma mixing and hybridization processes at the alkalic, silicic, Torfajökull central volcano triggered by tholeiitic Veidivötn fissuring, south Iceland

Blake, Stephen

doi:10.1016/0377-0273(84)90033-7

Cited by 63 publications

(38 citation statements)

References 34 publications

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“…Effusive dacite to rhyolite eruptions are significant but relatively rare occurrence and generally have produced small volume (<0.2 km 3 ) subaerial block lavas, coulees and domes as well as steep-sided subglacial domes and table mountains ranging in volume from <0.1 to ∼5 km 3 (Saemundsson, 1972;Blake, 1984;Macdonald et al, 1990;McGarvie et al, 1990;Tuffen et al, 2001Tuffen et al, , 2002. The aspect ratio of block lavas and coulees in Iceland is typically 0.02-0.05, which is very low compared to the typical aspect ratio of ∼0.1 for the same flow types in other volcanic regions (Walker, 1973a).…”

Section: Effusive Eruptionsmentioning

confidence: 99%

Volcanism in Iceland in historical time: Volcano types, eruption styles and eruptive history

Thordarson

Larsen

2007

Journal of Geodynamics

507

454

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The large-scale volcanic lineaments in Iceland are an axial zone, which is delineated by the Reykjanes, West and North Volcanic Zones (RVZ, WVZ, NVZ) and the East Volcanic Zone (EVZ), which is growing in length by propagation to the southwest through pre-existing crust. These zones are connected across central Iceland by the Mid-Iceland Belt (MIB). Other volcanically active areas are the two intraplate belts ofÖraefajökull (ÖVB) and Snaefellsnes (SVB). The principal structure of the volcanic zones are the 30 volcanic systems, where 12 are comprised of a fissure swarm and a central volcano, 7 of a central volcano, 9 of a fissure swarm and a central domain, and 2 are typified by a central domain alone.Volcanism in Iceland is unusually diverse for an oceanic island because of special geological and climatological circumstances. It features nearly all volcano types and eruption styles known on Earth. The first order grouping of volcanoes is in accordance with recurrence of eruptions on the same vent system and is divided into central volcanoes (polygenetic) and basalt volcanoes (monogenetic). The basalt volcanoes are categorized further in accordance with vent geometry (circular or linear), type of vent accumulation, characteristic style of eruption and volcanic environment (i.e. subaerial, subglacial, submarine).Eruptions are broadly grouped into effusive eruptions where >95% of the erupted magma is lava, explosive eruptions if >95% of the erupted magma is tephra (volume calculated as dense rock equivalent, DRE), and mixed eruptions if the ratio of lava to tephra occupy the range in between these two end-members. Although basaltic volcanism dominates, the activity in historical time (i.e. last 11 centuries) features expulsion of basalt, andesite, dacite and rhyolite magmas that have produced effusive eruptions of Hawaiian and flood lava magnitudes, mixed eruptions featuring phases of Strombolian to Plinian intensities, and explosive phreatomagmatic and magmatic eruptions spanning almost the entire intensity scale; from Surtseyan to Phreatoplinian in case of "wet" eruptions and Strombolian to Plinian in terms of "dry" eruptions. In historical time the magma volume extruded by individual eruptions ranges from ∼1 m 3 to ∼20 km 3 DRE, reflecting variable magma compositions, effusion rates and eruption durations.All together 205 eruptive events have been identified in historical time by detailed mapping and dating of events along with extensive research on documentation of eruptions in historical chronicles. Of these 205 events, 192 represent individual eruptions and 13 are classified as "Fires", which include two or more eruptions defining an episode of volcanic activity that lasts for months to years. Of the 159 eruptions verified by identification of their products 124 are explosive, effusive eruptions are 14 and mixed eruptions are 21. Eruptions listed as reported-only are 33. Eight of the Fires are predominantly effusive and the remaining five include explosive activity that produced extensive tephra layers...

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Section: Effusive Eruptionsmentioning

confidence: 99%

Volcanism in Iceland in historical time: Volcano types, eruption styles and eruptive history

Thordarson

Larsen

2007

Journal of Geodynamics

507

454

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“…According to one interpretation [Blake and Fink, 1987; Vogel et at., 1989] the Obsidian Dome eruption tapped a dike in which the two end member magmas were density-stratified (marie below silicic). The higher initial effusion rate selectively drew the less viscous mafic lava up through the overlying silicic cap [Blake, 1984]; as the eruption rate waned, the mafic/silicic interface was depressed and the more silicic magma came up the conduit. Our morphologic results can be used to place bounds on this transition: we infer that during the early marie stage the rate declined from 11 to 3 m3/s, while in the later more silicie stage the rate decreased further from around 3 to 0.6 m3/s.…”

Section: Santiaguitomentioning

confidence: 99%

Morphology, eruption rates, and rheology of lava domes: Insights from laboratory models

1998

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Abstract. The growth of lava domes can be either quiescent or violent, with transitions between styles of behavior commonly occurring with little warning. Here we propose that the behavior depends on the eruption rate, the magma theology, and the thickness of the cooling surface. We present a model, based on laboratory simulations, field measurements, and photographic analysis, that relates the morphology and texture of a dome to the thickness of its cooled carapace, and thence to eruption conditions. A sequence of four main types of dome (spiny, lobate, platy, and axisymmetric) is identified in laboratory analog experiments with a Bingham plastic. These regimes are associated with progressively higher effusion rates, lower cooling rates, lower yield strengths, and (in real lava flows) decreasing tendency for explosive decompression during flow front collapse and are ordered according to the value of a single dimensionless number. The model allows an estimate of the yield strengths of the magma forming active domes based on data for the effusion rate and composition. It also permits the eruption rates of prehistoric or extraterrestrial lava domes and flows to be appraised from their morphology, if their compositions can be estimated. A comparison with the laboratory results suggests that the Venusian "pancake domes" are likely to have basaltic to basaltic andesitic composition.

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“…All collected samples were glassy throughout, and hydrated (perlitised) samples were avoided wherever possible, as were localities that showed evidence of postquenching movement. One sample contained a mafic Gunnarsson et al (1998) and Larsen (1984) b Simplified geological map of Torfajökull, based on Gunnarsson et al (1998);McGarvie (1984); McGarvie et al (2006) and Blake (1984) inclusion several centimeters across, with a discrete but crenulated contact with the obsidian. This inclusion was analysed for geochemistry.…”

Section: Sampling Methodsmentioning

confidence: 99%

“…More than 250 km 3 of rhyolite has been erupted at the complex in numerous, mostly subglacial eruptions (McGarvie 1985). Holocene rhyolite eruptions at Torfajökull have been triggered by laterally propagating tholeiitic dykes from the ERZ intersecting rhyolitic magma chambers beneath Torfajökull (Blake 1984;Larsen 1984;McGarvie 1984;Mørk 1984;McGarvie et al 1990). These dykes propagated from the Veiðivötn system and have originated from Bárðarbunga central volcano (Fig.…”

Section: Bláhnúkur and Its Geological Settingmentioning

confidence: 99%

Using dissolved H2O in rhyolitic glasses to estimate palaeo-ice thickness during a subglacial eruption at Bláhnúkur (Torfajökull, Iceland)

2012

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The last decade has seen the refinement of a technique for reconstructing palaeo-ice thicknesses based on using the retained H 2 O and CO 2 content in glassy eruptive deposits to infer quenching pressures and therefore ice thicknesses. The method is here applied to Bláhnúkur, a subglacially erupted rhyolitic edifice in Iceland. A decrease in water content from ∼0.7 wt.% at the base to ∼0.3 wt.% at the top of the edifice suggests that the ice was 400 m thick at the time of the eruption. As Bláhnúkur rises 350 m above the surrounding terrain, this implies that the eruption occurred entirely within ice, which corroborates evidence obtained from earlier lithofacies studies. This paper presents the largest data set (40 samples) so far obtained for the retained volatile contents of deposits from a subglacial eruption. An important consequence is that it enables subtle but significant variations in water content to become evident. In particular, there are anomalous samples which are either water-rich (up to 1 wt.%) or water-poor (∼0.2 wt.%), with the former being interpreted as forming intrusively within hyaloclastite and the latter representing batches of magma that were volatile-poor prior to eruption. The large data set also provides further insights into the strengths and weaknesses of using volatiles to infer palaeo-ice thicknesses and highlights many of the uncertainties involved. By using examples from Bláhnúkur, the quantitative use of this technique is evaluated. However, the relative pressure conditions which have shed light on Bláhnúkur's eruption mechanisms and syn-eruptive glacier response show that, despite uncertainties in absolute values, the volatile approach can provide useful insight into the mechanisms of subglacial rhyolitic eruptions, which have never been observed.

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Magma mixing and hybridization processes at the alkalic, silicic, Torfajökull central volcano triggered by tholeiitic Veidivötn fissuring, south Iceland

Cited by 63 publications

References 34 publications

Volcanism in Iceland in historical time: Volcano types, eruption styles and eruptive history

Volcanism in Iceland in historical time: Volcano types, eruption styles and eruptive history

Morphology, eruption rates, and rheology of lava domes: Insights from laboratory models

Using dissolved H2O in rhyolitic glasses to estimate palaeo-ice thickness during a subglacial eruption at Bláhnúkur (Torfajökull, Iceland)

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