Re: Is there a formula to measure how powerful an explosion is by it's size?

Isaac: 

Check out another MadSci entry first:   
madsci/907545968.As.r.html

The volume of conventional explosive may be prohibitive if you're trying 
to write a credible sci-fi (I sure hope that's the case): break out the 
cement mixers for this one.  TNT's density as an exclusive compound (no 
sawdust, primers, plasticisers, wrappers, etc) is 1.654 gm/cubic cm.  Do 
the algebra, I think you'll find that to get the desired blast radius, 
you'd have to replace most of the pavement in the parking lots and streets 
with pure TNT, or mix it with a plasticiser and start filling in peoples' 
pools as well.  If I did my math right, one megaton (1 million tons) of 
pure TNT fills a volume of about 158 million gallons.  That's about what 
the whole US uses in water every day to irrigate farmland. (according to  
http://www.cvwater.org/facts.htm  

Research of some historical wartime atrocities might shed light on 
relative destructive power, but remember, this is not a linear 
relationship, TNT's not the most potent conventional explosive, and mother 
nature always has a way of surprising scientists.

For more on momma nature's contributions, the eruptions that created the 
Yellowstone Caldera in Wyoming 
(http://vulcan.wr.usgs.gov/Volcanoes/Yellowstone/description_yellowstone.ht
ml) 600,000 years ago (give or take) were probably equivalent to hundreds 
of thousands of megatons, and the crater from that is only about 60 km in 
diameter, not nearly the size of your tri-state area.  

Meteorites are pretty powerful, too.  The kinetic energy of something 
massive like nickel-iron turns into heat and motion when the gravity-
assisted freefall stops.
 http://www.glasslock.com/i
ntro_to_airblast.htm  
This link will take you to some more of the less-weighty calculus involved 
in air blast theory.  Air blasts and ground blasts vary greatly, due to 
the density of the media and the resistance provided by the ground in 
each. 

Views from space-
Unless you happen to see an explosive catastrophe when the area is in the 
dark, or covered by high clouds, it would have to be significant against 
the background.  About 2/3 of the chemical energy expended in an explosion 
is wasted in fire.  By comparison to the detonation reaction, this is 
truly a waste, but it shows up in the dark.  (But the plasma that's 
generated would glow too, more fodder for sci-fi novels)  Cloud cover, 
assuming the blast was directed up (path of least resistance when in a 
hole is "up") would be a great indicator of disturbance, and the debris 
would make for some fantastic sunsets for your hero to fly off into.  I 
would recommend looking at some pictures of earth from space and basing 
your blast size roughly on landmarks, then using some of these other 
resources to make your own back-calculations.  

Best of luck in your figurings!   --Sarah