Volcanic Archives of Past Glacial Environments: Tindfjallajökull Volcano, Iceland

Moles, Jonathan (2019). Volcanic Archives of Past Glacial Environments: Tindfjallajökull Volcano, Iceland. PhD thesis The Open University.

DOI: https://doi.org/10.21954/ou.ro.0000f2a5


Volcanoes preserve evidence of past glacial environments in the characteristics of their erupted products and in the sediments and landforms that occupy their flanks. By investigating volcanic stratigraphies and by dating palaeoenvironmental evidence, the glacial history of volcanic regions can be reconstructed. This thesis presents a geological and palaeoenvironmental survey of Tindfjallajökull volcano (Eastern Volcanic Zone, Iceland), followed by a focussed study of the glacial environments associated with the Ring Fracture Rhyolites eruption of neighbouring Torfajökull volcano.

Geological mapping, supplemented by whole-rock geochemistry and 40Ar/39Ar geochronology, gives insights into the evolution of Tindfjallajökull during the late Pleistocene. Prior to 358 ± 15 ka, a basalt-dominated stratocone of lavas and fragmental rocks was constructed, which was then capped with rhyolitic and basaltic lavas. Following this stage, there was a period of erosion and further rhyolitic volcanism occurred in the area of the present-day summit (126 ± 18 ka). Minor basaltic to trachyandesitic and basaltic andesitic flank eruptions continued through to the end of the last glacial period. Eruptions have commonly interacted with ice and the resulting glaciovolcanic deposits provide a record of fluctuating glacial environments on the volcano.

The Torfajökull Ring Fracture Rhyolites eruption (~55 ka) breached an ice sheet >400 m thick, dispersing tephra ‘II-RHY-1’ up to 2300 km from Iceland and depositing the Thórsmörk Ignimbrite in an area of little or no ice ~30 km from source. Due to the presence of the II-RHY-1 tephra horizon in regional palaeoclimate records (e.g. the Greenland ice cores), the eruption can be precisely dated to the end of Greenland Interstadial 15.2. The widely dispersed products of the eruption are used to reconstruct coeval glacial environments in southern Iceland and across the wider North Atlantic region.

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