Building Ice-Age Dyngjufjöll: Processes, Products and Environments

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The processes, products and paleoenvironments of large volume, polygenetic, ice-confined volcanoes are very poorly known. Dyngjufjoll ("Askja"), in Iceland, is one of the largest and best exposed, formerly ice-confined,basaltic volcanoes on Earth, but previous work has concentrated on its more recent Holocene (i.e. ice-free) evolution. This project will focus on its older Pleistocene history by targeting one large massif (Austurfjoll) that preserves several hundred meters of glaciovolcanic rocks. There has been considerable interest recently in the role of volcanogenic, subglacial ice melting and drainage as a lubricant for rapid ice sheet movement, and its potential for sheet destabilization. Also, source area processes and products of large-volume volcanogenic meltwater floods (i.e.jokulhlaups)are a significant hazard to infrastructure (roads, bridges) and the local economy in south Iceland. The results of this study will help close some gaps in knowledge regarding the geologic and environmental impacts of volcano-ice interaction processes. Volcanoes like Dyngjufjoll are also the most relevant terrestrial analogs to constraining models of the interaction of large long-lived basaltic shield volcanoes and ice on Mars. The study will be conducted as part of an international collaboration with scientists from the UK and Iceland.This project will offer insights into two relevant aspects of the meltwater source region, namely temporal variations in the overlying ice thickness and the nature of water drainage and ponding, including possible jokulhlaup (i.e. release of large-volume volcanogenic meltwater) events. There are no studies of the record of jokulhlaups at a volcanic edifice source. Volatile analysis of pillow rind glass at Austurfjoll will help constrain estimates of paleo-ice thicknesses in central Iceland, and models that link deglaciation with increased rates of volcanism in this area. The age of the Dyngjufjoll glaciovolcanic massifs are currently unknown, but up to 16 terrestrial glacial events have been recognized in Iceland since 2.5Ma, so there is potential for these rocks to record evidence of pre-late glacial maximum ice thicknesses. It is proposed to apply an integrated approach to stratigraphy using detailed quantitative glass texture and component analysis, geochemical analysis, 40Ar-39Ar dating, detailed structural and facies mapping and logging. This project and approach to correlation is particularly relevant to interpreting the very many (1000) fissure-erupted, glaciovolcanic, clastic-dominated sequences (i.e. 'tindars') in Iceland, which represent an enormous database on the glacial history of Iceland. The results of this project will help refine the criteria by which the presence of former ice in glaciovolcanic (particularly clastic) sequences is recognized, and hence contribute to the growing use of such rocks as indicators of past climate.