In reply to David Jonsson's message of Wed, 17 Jun 2009 14:48:21 +0200: Hi David, [snip] >> > The magma is hot becasue it is pressurised.
This is not the only reason it is hot. There is also *at least* radioactive decay. (And perhaps also some CF considering the small amount of Tritium that is occasionally also detected - though this could also be a byproduct of spontaneous fission). >>> When you pick >> it >> >up to earth it will expand and cool. >> [snip] >> Volcano. >> > >OK, I have to admit I haven't studied the magma but only the crust. And it >surprises me much that the magma has an adiabatic gradient of only 0.3 K/km. >How was that calculated? You did the calculation. AFAIK others just measure it. > >Admit that the crust will cool if picked up. Certainly something will cool (the energy to fight gravity has to come from somewhere), but what comes to the surface may not be the same thing that cools. I'm not sure how relevant it is, but I did the following simple calculation, which assumes that the gravitational energy of a falling body is all converted into heat. For stone, the specific heat is about 2 cal/gm*K. If we divide g (gravitational acceleration at the Earth's surface) by this, we get 11.7 K/km. Regards, Robin van Spaandonk http://rvanspaa.freehostia.com/Project.html
