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

Abstract

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...

Snæfellsjökull volcano-centred ice cap landsystem, West Iceland

“…The multi-lobed ice cap covers an area of almost 12.5 km 2 . It occupies the summit and fills the caldera of an active stratovolcano that reaches a maximum elevation of 1446 m above sea level (Thordarson & Larsen, 2007). The volcano is a stratovolcano-tuya hybrid formed in the trans-current fault-zone of the North Atlantic spreading ridge (Hards, Kempton, Thompson, & Greenwood, 2000;Thordarson & Larsen, 2007).…”

“…It occupies the summit and fills the caldera of an active stratovolcano that reaches a maximum elevation of 1446 m above sea level (Thordarson & Larsen, 2007). The volcano is a stratovolcano-tuya hybrid formed in the trans-current fault-zone of the North Atlantic spreading ridge (Hards, Kempton, Thompson, & Greenwood, 2000;Thordarson & Larsen, 2007). The highly variable volcanic conditions associated with this hybrid feature makes the geology of the area relatively complex (Figure 2), characterized by a suite of mildly alkali basalts and peralkaline rhyolites that are geochemically similar to those from the Icelandic Torfajökull volcano (Hards et al, 2000;MacDonald, McGarvie, Pinkerton, Smith, & Palacz, 1990).…”

Segmented lateral dyke growth in a rifting event at Bárðarbunga volcanic system, Iceland

“…It has an associated fissure swarm 11 extending 115 km to the SW and 55 km to the NNE. Activity in the last 2000 years includes both subglacial eruptions as well as major effusive fissure eruptions, with 23 verified eruptions in the last 1100 years 12 .…”

Extended SO2 outgassing from the 2014–2015 Holuhraun lava flow field, Iceland

“…The eruption produced 1.6 ± 0.3 km 3 of lava, forming an 84.1 ± 0.6 km 2 lava flow field (Gíslason et al 2015). This classifies the eruption as a flood basalt eruption following Thordarson and Larsen (2007). This makes the Holuhraun eruption the most voluminous effusive eruption in Iceland since the 1783-1784 Laki eruption (Schmidt et al 2015).…”