Complex circular subsidence structures in tephra deposited on large blocks of ice: Varða tuff cone, Oræfajokull, Iceland.

ABSTRACT: Several broadly circular structures up to 16 m in diameter, into which higher strata have sagged and locally collapsed, are present in a tephra outcrop on southwest Öræfajökull, southern Iceland. The tephra was sourced in a nearby basaltic tuff cone at Varða. The structures have not previously been described in tuff cones, and they probably formed by the melting out of large buried blocks of ice emplaced during a preceding jökulhlaup that may have been triggered by a subglacial eruption within the Öræfajökull ice cap. They are named ice-melt subsidence structures, and they are analogous to kettle holes that are commonly found in proglacial sandurs and some lahars sourced in ice-clad volcanoes. The internal structure is better exposed in the Varða examples because of an absence of fluvial i

SUBMITTER: Smellie JL 

PROVIDER: S-EPMC7175720 | biostudies-literature | 2016

REPOSITORIES: biostudies-literature