Glacier caves and subglacial water.
Glacier caves, created when streams flowing down the adjacent valley side continue beneath the ice, tend to be elongated tunnels of approximately semi-circular cross-section, sloping down towards the centre of the glacier. Caves formed as a glacier loses contact with an irregular surface over which it is sliding are particularly common where the bed gradient increases: many are found against rock steps, and their length and cross-sectional form depend on the height of the up-glacier wall, the gradient of the floor along the ice flow direction, and the rate of sliding. Water within the caves may freeze onto cold rock surfaces. Water at a glacier bed may be in the form of a film which effectively lubricates the glacier-rock interface by submerging small irregularities which impede sliding, or it may flow through a system of distinct channels. Areas of subglacial terrain exposed around the margins of glaciers which have retreated in recent years provide evidence of glacial basal drainage systems. Glaciers and their hydrological systems are unlikely to be sufficiently stable for a long enough period both to initiate cave formation in calcareous bedrock and also to cause extensive development or modification in relatively unchanging conditions: most caves in soluble carbonates affected by glacial processes are likely to have experienced periods of development in widely-different conditions.
Glacier Caves
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Image: a glacier cave in Greenland, featured in the IMAX Film amazing caves, © MacGillivray Freeman Films.
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Caves inside ice are only possible in ice, which does not melt away every year. This kind of ice is called glacier, and is found all over the world. Huge glaciers cover the north and south pole. Other glaciers cover mountains in Greenland, Iceland, Norway, New Zealand and Alaska.
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Image: a glacier cave in Greenland, featured in the IMAX Film amazing caves, © MacGillivray Freeman Films.
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To remove ice from inside a glacier, all we need is a little bit of energy (aka warmth). The ice melts, and if there are cracks in the ice, the water flows out of the glacier.
Many glaciers of the world are in areas with seasons. In the warm season the surface of the ice starts to melt and the water flows down the ice shield. As it is a little warmer than the ice it also melts a little bit of ice where it flows, and so the water soon forms a gorge. As the ice is able to flow, the gorge closes some time after the water stops to flow. Only water flowing continually will keep the passage clear. But as it flows on the bottom of the gorge, the upper part of the gorge closes and the gorge becomes a cave.
A very special thing are the glacier caves of Iceland. This island has many volcanic regions, so it is rather common that volcanoes or warm springs are located below glaciers. This volcanic warmth melts ice at the bottom of the glacier thus producing a cavern inside. If the water has a way to flow out, it is air filled, if not it is water filled.
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