Postglacial eruptive history of the Askja region, North Iceland

Margaret E Hartley,Alexandra De Joux,Thorvaldur Thordarson

doi:10.1007/s00445-016-1022-7

Margaret E Hartley, Alexandra De Joux + Show 1 more

Open Access

https://doi.org/10.1007/s00445-016-1022-7

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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 Vatnaoldur (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 km3 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.

Highlights

Numerous studies have examined the relationship between volcanism and glacial cycles, both on local and global scales (e.g. Rampino et al 1979; Nakada and Yokose 1992; Jellinek et al 2004; Huybers and Langmuir 2009; Watt et al 2013 and references therein)
At least 39 km3 of basaltic lava has been erupted at Askja since the area became ice-free; an additional volume of 9.6–16.5 km3 forms the 300–500 m-thick lava pile that partially fills Askja caldera
Much of Askja caldera floor is occupied by lava flows that post-date 1477 AD, while the oldest lavas exposed in the caldera floor pre-date 1158 AD

Summary

Introduction

Numerous studies have examined the relationship between volcanism and glacial cycles, both on local and global scales (e.g. Rampino et al 1979; Nakada and Yokose 1992; Jellinek et al 2004; Huybers and Langmuir 2009; Watt et al 2013 and references therein). It has been estimated that global subaerial volcanic activity increased by a factor of 2–6 between 12 and 7 ka, due to enhanced eruption rates in deglaciating regions (Huybers and Langmuir 2009). There is considerable interest in the feedbacks between subaerial and submarine CO2 emissions and glacial cycles: recent papers have proposed that pulsing of ocean ridge magma productivity, and CO2 emissions, may feed back into climate cycles and possibly contribute to the abrupt ending of ice ages on a 100-kyr timescale (Burley and Katz 2015; Crowley et al 2015; Olive et al 2015; Tolstoy 2015).

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