<Li> The strongest types of eruptions, with a VEI of 8, are so - called "Ultra-Plinian" eruptions, such as the most recent one at Lake Toba 74 thousand years ago, which put out 2800 times the material erupted by Mount St. Helens in 1980 . </Li> <Li> Hekla in Iceland, an example of basaltic Plinian volcanism being its 1947--48 eruption . The past 800 years have been a pattern of violent initial eruptions of pumice followed by prolonged extrusion of basaltic lava from the lower part of the volcano . </Li> <Li> Pinatubo in the Philippines on 15 June 1991, which produced 5 km (1 cu mi) of dacitic magma, a 40 km (25 mi) high eruption column, and released 17 megatons of sulfur dioxide . </Li> <P> Phreatomagmatic eruptions are eruptions that arise from interactions between water and magma . They are driven from thermal contraction (as opposed to magmatic eruptions, which are driven by thermal expansion) of magma when it comes in contact with water . This temperature difference between the two causes violent water - lava interactions that make up the eruption . The products of phreatomagmatic eruptions are believed to be more regular in shape and finer grained than the products of magmatic eruptions because of the differences in eruptive mechanisms . </P>

How do icelandic volcano eruptions differ from hawaiian eruptions