How big of an area will the ash plume affect?
That’s a very good question because, depending on the size of the eruption, it could either affect just the volcano itself or it could affect the entire planet. There have been eruptions in the past. Tambora was one, Krakatoa – back in the 1800’s, and Katmai in 1912. Those types of eruptions are so large and they put so much ash in the atmosphere that they would actually circle around Earth with the winds and cause climactic change in essentially the entire planet. There was one instance, and I cannot remember which eruption it was, back in the 17 or 1800’s, there was actually a period of starvation in Europe because the crops wouldn’t grow because there was so much ash in the air that the sun was blocked and the temperature dropped by several degrees and hence, destroyed all the agriculture of the time. So it definitely can have a global impact on the entire planet. But those are for very, very large eruptions. It is not very common.
