# How much lava is there in earth?

by DrDu
Tags: earth, lava
 Sci Advisor P: 3,593 I was reading about the earths structure and learned that the mantle is solid, although it can deform plastically. In fact this follows from possibility of transversal seismic waves to propagate. This leaves me with the question where the magma that we observe in volcanos is formed and how much there is present at the crust-mantle boundary.
 Earth sciences news on Phys.org
P: 9,488
 Quote by DrDu I was reading about the earths structure and learned that the mantle is solid, although it can deform plastically. In fact this follows from possibility of transversal seismic waves to propagate. This leaves me with the question where the magma that we observe in volcanos is formed and how much there is present at the crust-mantle boundary.
I'm sure you've checked out wiki?
http://en.wikipedia.org/wiki/Magma

Here are two loosely related but interesting articles

THE DEEPEST HOLE
http://www.damninteresting.com/the-deepest-hole/

Drillers Accidentally Create First Live Magma Observatory
http://www.wired.com/wiredscience/20...gmaobservator/
 Sci Advisor P: 3,593 Thank you Greg! This only leaves open my question on the quantity of magma present at the crust-mantle boundary.
 PF Gold P: 5,458 How much lava is there in earth? That's not lava but magma. I'm not aware of trustworthy estimates about total quatities. There are numbers mentioned here but not tied a reference.
 Sci Advisor P: 3,593 Yes, you are right, I should have written magma in the tiltle, not lava. I have been reading the "subduction" article before but found it quite dubious, e.g. "The supercritical water, which is hot and more buoyant than the surrounding rock, rises into the overlying mantle where it lowers the pressure in (and thus the melting temperature of) the mantle rock to the point of actual melting, generating magma." I can't see how rising water can lower the pressure.
P: 747
 Quote by DrDu Yes, you are right, I should have written magma in the tiltle, not lava. I have been reading the "subduction" article before but found it quite dubious, e.g. "The supercritical water, which is hot and more buoyant than the surrounding rock, rises into the overlying mantle where it lowers the pressure in (and thus the melting temperature of) the mantle rock to the point of actual melting, generating magma." I can't see how rising water can lower the pressure.
The water pushes the grains in the rock apart, counter to the loading stress due to the overburden. The net is a drop in the effective stress.

c.f http://en.wikipedia.org/wiki/Effective_stress
 Sci Advisor P: 3,593 I did some reading. Apparently water reduces the melting temperatures by depolymerizing silicates in the melt thereby increasing the entropy of the melt: www.people.fas.harvard.edu/~langmuir/Papers/Katz G3 03.pdf Makes much more sense.
 Sci Advisor P: 3,593 I found some numbers on how much magma is generated by locations (subduction zones, hot spots etc) in H Bahlburg, C Breitkreuz, Grundlagen der Geologie, Spektrum Verlag, 2012. . The sum is of the order of 1 km^3 per year. I don't have the precise numbers at hand right now.
P: 747
 Quote by DrDu I found some numbers on how much magma is generated by locations (subduction zones, hot spots etc) in H Bahlburg, C Breitkreuz, Grundlagen der Geologie, Spektrum Verlag, 2012. . The sum is of the order of 1 km^3 per year. I don't have the precise numbers at hand right now.
That sounds small to me. It appears you are missing mid ocean ridges, which add about 20 km^3 per year.
 Sci Advisor P: 3,593 You are right. The numbers from the book are location intrusive extrusive subduction zone 8 0.8 mid oceanic ridges 18 3 intra plate volcanoes oceanic 2 0.4 continental 1.5 0.1
 P: 2 Lava being the unsolidified molten rock material deposited on the surface of Earth? A fraction of a fraction of a fraction of a percent. As defined as a solidified rock, the percentage of Earth's crust is over 66% hardened lava, in the form of basalt.
P: 275
 Quote by dannielwang Lava being the unsolidified molten rock material deposited on the surface of Earth? A fraction of a fraction of a fraction of a percent. As defined as a solidified rock, the percentage of Earth's crust is over 66% hardened lava, in the form of basalt.
You seem to have taken the view that the oceans are absalt, the continents (granite) are not, and so the ratio is as you have defined it. However you have failed to take into account the much greater thickness of the continental crust.
 Mentor P: 26,523 Please link to the source so we can verify, thank you. Also, this is a reminder to everyone posting "facts", you need to post a link to your source when you post facts about something that is not general knowledge, it's the only way we can determine which information is most accurate.

 Related Discussions Earth 8 General Discussion 16 Introductory Physics Homework 3 Introductory Physics Homework 1