Sheppard tells McKay that they are not naming the Ancient ship the Enterprise. In Stargate SG-1 (1997), Samantha Carter has a similar conversation with Jack O'Neill regarding the U.S. ship that came to be called Prometheus (see Unnatural Selection (2002)).
Supervolcanoes, by definition, eject over 1000 cubic kilometers of stuff. Some eruptions are fairly quick and explosive but some simply ooze out lava constantly for several thousand years. There have been several periods of supervolcano eruption in Earth's past and they tend to cause periods of mass extinction.