AV俱乐部

Ice contact volcanism, and specifically subglacial volcanism, can provide information about paleo environments such as the extent and thickness of former glaciers and ice sheets. In southwest Iceland, approximately 30 km southeast of Reykjav铆k on the Reykjanes Peninsula, the regions of Northern Bl谩fj枚ll, V铆filsfell, and Arnar镁煤fur contain structures associated with Pleistocene ice contact volcanism. This study combines remote sensing classification of multispectral satellite imagery, field observations, and geochemical analysis to determine the relationship between these features. Remote sensing classification of SPOT 5 imagery using Geographic Information Systems (GIS) generates 16 significant spectral clusters. Determination of significant clusters and their spatial distribution facilitates subsequent field investigations. Ground truthing of Northern Bl谩fj枚ll reveals a flat topped volcano with steep sides that consists of basal pillow lavas, pillow breccia, altered hyaloclastite (palagonite), flow foot breccia, welded scoria, and superincumbent subaerial lava flows. V铆filsfell directly overlies Northern Bl谩fj脰ll and encompasses a conical mound of palagonite with isolated welded scoria, volcanic bombs, dykes with pillowed surfaces, and peripheral slump deposits. Arnar镁煤fur comprises a series of linearly oriented discrete mounds with rhythmically layered fine grained palagonite and clast supported beds that include varying proportions of armoured lapilli. Beds typically contain flow indicators such as climbing ripples, cross beds, and flutes. Electron microprobe analysis of major element concentrations in volcanic glass reveals that Northern Bl谩fj枚ll, V铆filsfell, and Arnar镁煤fur have indistinguishable olivine normative tholeiite compositions. Northern Bl谩fj枚ll is a tuya that emerged from a deep englacial melt water lake with a surrounding ice thickness exceeding 400 m, according to the passage zone elevation above the surrounding plain. V铆filsfell is a subglacial mound that formed beneath thin ice conditions with episodic melt water drainage during its emplacement. Arnar镁煤fur is an ice confined hyaloclastite flow deposit that combines characteristics of pyroclastic density currents, turbidites, and eskers. Statigraphic relationships suggest that Arnar镁煤fur formed in association with the V铆filsfell eruption as a result of gravity controlled mobilization of unconsolidated volcaniclastic material into an ice confined melt water drainage system. The chemical homogeneity of Northern Bl谩fj枚ll, V铆filsfell, and Arnar镁煤fur suggest a common magma source and rapid emplacement of the volcanic deposits relative to the evolution of the melt.

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Pages: 195
Supervisor: Barrie Clarke