twisted bits said:
The Mt St. Helens or even Krakatau eruption would look like a belch. It would be 500m + in height and the velocity would be in excess of 500 mph.
Actually, both are just pimples compared to really large explosive volcanic eruptions. St helens put out about 1/2 cubic Km in 1980 and Krakatoa, maybe 10 cubuc Km. The largest eruptions are almost always associated with continental collapse caldera complexes. Mt Pinatubo is a small one that had the largest eruption of the 20th century at 15 cubic Km.
The largest known eruptions came from the Long Valley Caldera in Ca. which put out around 1000 cubic Km that is known as the Bishop Tuff. The Jemez Caldera in NM put out the Bandolier Tuff in excess of 500 cubic Km about 700,000 years ago and Yellowstone had a similar sized eruption. These are on the order of 1000 to 2000 times the size of St Helens and 50 to 100 times Krakatoa. Luckily, they are mostly inland and don't generate tsunamis.
Major earthquakes, are a different breed of cat than volcanos. They may rupture along tens to hundreds of miles and suddenly move one block tens to hundreds of feet WRT the other. They often happen under water and really big ones can occur at both subduction zones like the one off Sumatra (relative motion upwards on 30° to 40° dipping fault zone) or on transform zones like the San Andreas (relative motion horizontal as fault blocks move past one another). The largest quakes generally have components of both types of motion.
