GEOLOGY

Detailed explanation-1: -The strongest types of eruptions, with a VEI of 8, are so-called “Ultra-Plinian” eruptions, such as the one at Lake Toba 74 thousand years ago, which put out 2800 times the material erupted by Mount St. Helens in 1980. Hekla in Iceland, an example of basaltic Plinian volcanism being its 1947–48 eruption.

Detailed explanation-2: -The most powerful eruptions are called “plinian” and involve the explosive ejection of relatively viscous lava. Large plinian eruptions–such as during 18 May 1980 at Mount St. Helens or, more recently, during 15 June 1991 at Pinatubo in the Philippines–can send ash and volcanic gas tens of miles into the air.

Detailed explanation-3: -In Plinian eruptions the fragmentation of magma is very high and the surface area of fragments exposed to the atmosphere is, therefore, also high. Consequently, eruptions of this type are characterized by a higher efficiency in utilization of thermal energy than other volcanic eruptions.

Detailed explanation-4: -Plinian eruptions are extremely explosive eruptions, producing ash columns that extend many tens of miles into the stratosphere and that spread out into an umbrella shape. These large eruptions produce widespread deposits of fallout ash. Eruption columns may also collapse due to density to form thick pyroclastic flows.