Scale of volcanic activity. I am wondering if there is a simple computation (*) (using the mass, age, internal radioactive heating, magma viscosity, ...) that can give the order of magnitude of volcanic activity (measured for example by the volume of crust produced per year, thermal energy loss through eruptive activity,...). I know that astronomers do similar computations for stars, trying to estimate brightness, neutrino flux, lifetime, composition... (*) This computation could probably apply to any planet.

rocky Jacques D. Rutschmann

Dear Jacques,

I mentioned your question to Chuck Wood. Since Chuck spends the better part of most days thinking of space (he's Chair of the Space Studies Department), he promptly reminded me that modeling stars (ideal gases, homogeneous) is a lot easier then modeling the Earth (solid, liquids, gases; non-homogenous in composition, distribution in radioactive elements, and viscosity).

With that said lets do a simple computation. For 1 calorie of heat extracted from the mantle 0.01 g of melt is generated. Assuming a density of 3.2 gm/cc and a volume of 125 cubic km/year for new oceanic plate created at mid-ocean ridges (and probably ten other things I didn't even think of), about 5E12 watts of energy are transferred from the mantle to the surface by mid-ocean ridge volcanism.

So, I came up with this number and wondered if it means anything (does it say anything about the amount of thermal energy loss through eruptive activity). I found some interesting values for energy flow in the Earth. About 20-40 watts of energy are conducted from Earth's interior to the surface. So my value is not too far off and suggests volcanism plays a significant role in cooling the interior of the Earth. U.S. Energy consumption (in 1980) was 2.5E12 watts, roughly half the energy released by heat transfer at mid-ocean ridges.

Steve Mattox, University of North Dakota

Source of Information:
Harte, J., 1988, Consider a spherical cow, a course in environmental problem solving: University Science Books, Mill Valley, California, 283 p. 

Other Categories        Other Questions

To VolcanoWorld