Hyaloclastite

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Hyaloclastite under the microscope: shards of yellowish rock glass

A hyaloclastite is a consolidated pyroclastic rock form that consists largely of fragments of volcanic glass .

composition

Hyaloclastite is a hydrated tuff - breccia , which is rich in black volcanic glass. This occurs in the form of flat, angular fragments with a size of one millimeter to a few centimeters.

Several minerals are found in hyaloclastic rocks. Sideromelan is an olive-green, obsidian-like, basaltic glass that was quickly quenched in water. It is transparent and pure; in contrast to the more common tachylite, the scattered iron oxide crystals are missing .

The glass fragments are usually surrounded by a yellow or brown layer of palagonite , which is formed when sideromelan reacts with water.

Emergence

Hyaloclastites arise when lava cools under water or ice cover and are therefore characteristic rocks in the area of ​​subglacial or submarine volcanoes and of Tuyas . The fragmentation of the volcanic glass occurs by the force of a volcanic explosion or by thermal shock during rapid cooling.

literature

  • R. Batiza, JDL White (2000): Submarine lavas and hyaloclastite , in: H. Sigurdsson, B. Houghton, SR McNutt, H. Rymer, J. Stix (Eds.), Encyclopedia of Volcanoes. Academic Press, San Diego, CA, pp. 361-381. ISBN 978-0126431407
  • MT Gudmundsson, F. Sigmundsson, H. Björnsson (1997): Ice-volcano interaction of the 1996 Gjálp subglacial eruption, Vatnajökull, Iceland , in: Nature, 389: 954-957. doi : 10.1038 / 40122
  • WH Mathews (1947): "Tuyas", flat-topped volcanoes in northern British Columbia , in: Am. J. Sci., 245 (9): 560-570. doi : 10.2475 / ajs.245.9.560
  • JL Smellie, P. Skilling (1994): Products of subglacial volcanic eruptions under different ice thicknesses: two examples from Antarctica , in: Sedimentary Geology, 91 (1-4): 115-129. doi : 10.1016 / 0037-0738 (94) 90125-2
  • JW Head, L. Wilson (2003): Deep submarine pyroclastic eruptions: theory and predicted landforms and deposits , in: Journal of Volcanology and Geothermal Research, 121 (3-4): 155-193. doi : 10.1016 / S0377-0273 (02) 00425-0

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