Postglacial eruptive history of the Askja region, North Iceland

Abstract

Temporal variations in magma discharge rates on Iceland's neovolcanic rift zones have been associated with deglaciation. We have used tephrochronological and stratigraphic dating of 175 separate eruptive units to estimate volumetric output and reconstruct eruption rates in the Askja region over the postglacial period. We have identified 14 tephra layers that can be used as time marker horizons in the near vicinity of Askja, including the Vatnaöldur (871 ± 2 AD) tephra which has not previously been reported in surface cover profiles in this region. Our improved tephrochronological resolution indicates that, over the past c. 1,500 years, Askja has been significantly more active than has previously been recognised. A minimum of 39 km 3 of basaltic magma has been erupted at Askja since the area became ice-free at around 10.3 ka. The absence of the 7.2 ka Hekla 5 tephra from the Askja region suggests that all postglacial lavas now exposed at the surface are younger than 7.2 ka. Time-averaged magma discharge rates at Askja were highest between 7.2 and 4.3 ka. However, the available tephrochronological resolution is not sufficient to resolve any peak in volcanic activity following deglaciation.

Rhyolitic and dacitic component of the Askja 1875 tephra in southern and central Finland: first step towards a Finnish tephrochronology

“…These deposits are, however, chronologically and geochemically separated, and Stömyren tephra may represent another tephra originating in Askja which has yet to be identified in the proximal records. Recent research on the eruptive history of the Askja volcanic system reveals that more frequent eruptions have taken place during the Holocene than previously estimated (Hartley et al ., ), which creates a possibility for further identifications of Askja‐origin deposits through detailed cryptotephra investigations in northern Europe.…”

Ice-confined construction of a large basaltic volcano—Austurfjöll massif, Askja, Iceland

“…Askja does not have a typical tuya or tindar morphology like previously described central volcanoes (Herðubreið;Werner et al 1996). Askja comprises four glaciovolcanic massifs, at least three calderas, ample Holocene basaltic lavas, and lesser volumes of silicic volcanic including the 1875 plinian eruption deposit (Sigvaldason 1968;Carey et al 2009;Hartley et al 2016). This paper describes the deposits and geomorphology of the Austurfjöll massif ( Figure 1) that makes up the eastern wall of the 1875 caldera.…”

“…The Weichselian activity has a strong parallel in Holocene volcanism at Askja, where similar activity (i.e. fissure eruptions of modest volume) has persisted from the early Holocene to the present day (Annertz 1985;Höskuldsson 1987;Sigvaldason et al 1992;Kuritani et al 2011;Hartley et al 2016) the most recent eruption being in 1961 (Thorarinsson and Sigvaldason 1962). It is likely that other large basaltic volcanoes in Iceland that interacted with an ice sheet also preserve evidence of prolonged multi-vent, multi-fissure eruptions through multiple ice-confined lakes.…”

The Importance of Icelandic Ice Sheet Growth and Retreat on Mantle CO2 Flux

“…The 1-D forward model used is highly idealized, and yet the agreement between the observations and model is encouraging and suggests the compositional change observed in lavas erupted during the late-Pleistocene to early Holocene is due to rapid deglaciation ( (a) Nb concentrations from the center of extension out to 60 km from the center of extension. This will have been the case up until at least ∼14 ka, where either magmatism was suppressed or when eruptions occurred, they will have been beneath at least 1 km of ice cover (Hartley et al, 2016). (b) Predicted CO 2 flux from the series of vertical melting models.…”