I like that Wolfram Alpha will just do this one for you: http://www.wolframalpha.com/input/?i=volume+of+lake+superior+%2F+(area+of+north+america+%2B+area+of+so

I like that Wolfram Alpha will just do this one for you: http://www.wolframalpha.com/input/?i=volume+of+lake+superior+%2F+(area+of+north+america+%2B+area+of+south+america) http://www.wolframalpha.com/input/?i=volume+of+lake+superior... It struggles with the more esoteric aquifers, and doesn't understand "North and South America" as an object, but still pretty cool.