Mathematics – Logic
Scientific paper
Jan 1998
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1998lpico.953....2b&link_type=abstract
The First International Conference on Mars Polar Science and Exploration, Proceedings of the Conference held at Camp Allen, TX.
Mathematics
Logic
Glaciers, Glaciology, Iceland, Landforms, Volcanology, Land Ice, Lakes, Geomorphology, Volcanoes, Water, Topography
Scientific paper
About 11% (11,000 sq km) of Iceland is at present covered by temperate glaciers, ranging from small cirque glaciers to large ice caps. These glaciers are dynamically active with large mass turnover and high production of melt water. Lying on easily erodable beds, typical landforms are large outwash plains and moraines, as well as cirques, troughs, and U-shaped valleys. Surges and outburst floods from ice-dammed lakes are frequent. The presence of active volcanos beneath the glaciers adds dimensions to the erosional and sedimentological processes and their impact on landscapes. About 60% of glaciers in Iceland are underlain by the active neovolcanic zone, and outburst floods jokulhlaups) occur regularly from subglacial lakes at geothermal areas, occasionally due to subglacial eruptions. Their effects are seen in the transport and deposition of sediments over outwash plains and in the erosion of large canyons. Outburst floods from the subglacial lake Grimsvotn (one of the best-known localities in the ice cap Vatnajbkull) have occurred at 1-10-yr intervals, with a peak discharge of 600-40,000 cubic m/s at the outwash plain Skeioararsandur, a duration of 2 days to 4 weeks and a total volume of 0.5-4.0 cu km. Typically, the outlet-river discharge during jokulhlaups rises approximately exponentially as a function of time; falling rapidly after peaking. Such a discharge pattern can be explained as a flow through a single ice tunnel at the glacier bed. The flow is controlled mainly by tunnel enlargement due to melting of the walls by frictional heat generated by the flowing water. Occasionally the lake water may be above the melting point, expediating the expansion of the tunnel. Volcanic eruptions have caused tremendous jokulhlaups with dramatic impact on landforms. The observed high rate of melting during subglacial eruptions, suggest that magma is quenched from the melting temperature to 0C and fragmented into glass in a highly turbulent mixture with meltwater. During the initial phase of a volcanic eruption in 1996, meltwater was produced at the rate of 8000 cubic m/S. During the most violent eruptions, discharge of the jokulhlaups may rise in a few hours to a peak of several hundred thousand cubic meters per second. Some of these floods consist of a hyperconcentrated fluid-sediment mixture. Under the glaciers, volcanic eruptions produce hyaloclastite ridges and table mountains.
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