Interaction of Ice Sheet Loading, Tectonics and Subglacial and Subaerial Volcanism in Iceland
Abstract
Volcanism in Iceland is dominated by basaltic, rift-related eruptions. By making use of the density contrast between subaerially-formed lavas and subglacially-formed hyaloclastites, segments of the volcanic zones in Iceland have been studied with gravimetry to obtain the volume of, a) subaerially-erupted lava flows, and b) subglacially-erupted material. These data provide estimates of production rates of magma during the Holocene, and during late-Pleistocene glaciations, especially the Weichselian glaciation. The large volumes obtained for early Holocene lavas confirm a peak in magma productivity at the start of the Holocene, in some areas through the formation of large shield volcanoes. A likely cause for this peak in volcanism is enhanced decompressional melting in the mantle as the load of the Pleistocene ice sheet disappeared. The style of volcanic activity during glacial periods is very different from that of interglacial periods. During glacial periods the volcanic material is cooled very rapidly by interaction with ice and meltwater. This leads to formation of steep-sided mountains, mainly composed of pillow lava, hyaloclastite tuffs and breccias. During interglacial periods, shield volcanoes and extensive lava fields are created. The subglacial style of activity creates a rugged landscape that may later be partly buried by subaerial lavas during ice-free periods. Where grabens are active during glacial periods their subsidence is only to a limited extent compensated by accumulation of new material within the grabens. This is due to limited spreading of material erupted in subglacial eruptions; it is mainly piled up above the vents. At the start of interglacial periods the grabens are therefore deep and effective traps for lava. Large accumulations of lava may pond in the grabens and in valleys between hyaloclastite ridges. Estimates of magma production rates for the three areas studied so far indicate much higher rates during the Holocene than during the Weichselian glaciation.
- Publication:
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EGS - AGU - EUG Joint Assembly
- Pub Date:
- April 2003
- Bibcode:
- 2003EAEJA....12796G