During a volcanic eruption, lava, tephra (ash, lapilli, solid chunks of rock), and various gases, are expelled from a volcanic vent or fissure. Several types of volcanic eruptions have been distinguished by volcanologists. These are often named after famous volcanoes where that type of behavior has been observed. Some volcanoes may exhibit only one characteristic type of eruption during a period of activity, while others may display an entire sequence of types. Volcanic eruptions arise through three main mechanisms: Gas release under decompression causing magmatic eruptions Thermal contraction from chilling on contact with water causing phreatomagmatic eruptions Ejection entrained particles during steam eruptions causing phreatic eruptions (Heiken & Wholtez 1985 A supervolcanic eruption at Lake Toba around 74,000 years ago could have wiped out as much as 99% of the global human population, reducing the population from a possible 60 million to less than 10 thousand; see Toba catastrophe theory. However, this theory is not widely accepted because the evidence is disputed, and there have been, for instance, no remains found. The eruption is not listed here as it was pre-historic and outside the scope of this article. Also, the Thera eruption in the Aegean Sea between 1550 and 1650 B.C. may have caused a large number of deaths throughout the region, from Crete to Egypt. See also La Garita Caldera, Yellowstone Caldera, and Supervolcanoes. pzdr licze na najlpesza:]
