Now I may not be a science buff, but this concept is extremely interesting. Basically, it is just a volcanic eruption of such scale that it causes adverse effects on the environment not just nearby, but for hundreds or even thousands of miles in every direction. In the 1700’s a particularly powerful explosion in Iceland caused the direct death of some 9,000 people- as well as most of the nation’s livestock, leading to further death (and lots of it) as a result of starvation. The ash cloud caused by the eruption also caused a 9 degree plunge in the temperature in the US. How many volcanoes are there on Earth?