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Much of the research on subglacial volcanism has been conducted on basaltic volcanoes. Hence, a "classic" model for subglacial eruption has been developed, and describes many basaltic edifices quite well; intermediate and rhyolitic subglacial volcanoes have slightly different internal stratigraphies and lithological characteristics. A basaltic subglacial eruption typically begins with passive effusion of lava into a meltwater vault within the ice, forming a pile of pillow lavas which grows upwards. Pillow fragment breccias may be generated as pillows roll down the steep flanks of the edifice. As the meltwater chamber grows within the ice, a cauldron or depression forms in the ice above it, and ice and water both flow towards the vent area. As the eruption proceeds, eruptions typically become phreatomagmatic (explosive), generating hyaloclastite. |
| As fragmental material is generated, it rolls down the steep flanks of the volcano and commonly produces an outward-dipping, delta-like sequence. The growing volcanic pile may also be intruded by fresh lavas to form jointed units or dykes. Eventually, the ice cauldron above the vent melts through, forming a chimney. If the eruption ceases before the vent reaches the water's surface, a conical subglacial mound is formed. |
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If the eruption continues to until the volcanic pile breaches the water surface, eruption again becomes passive, with relatively flat-lying subaerial flows being deposited on the top surface of the pile. As subaerially-erupted lava enters the water at the flanks of the volcano's cap, it breaks up, rolls downslope, and continues adding to the delta-like sequence. The landform is now a tuya. The tuya's cap of subaerial lavas is more resistant to erosion than the hyaloclastite deposits, although hyaloclastite preservation potential is enhanced when it is altered to palagonite. |