http://www.sciencedaily.com/releases/2009/12/091231143142.htm

Learned of this over on sci.geo.earthquakes.

ScienceDaily (Jan. 4, 2010) — Scientists have successfully determined the permeability of the asthenosphere in the Earth's upper mantle and thus the rate at which melt rises to the Earth's surface: it flows up to 25 times faster than previously assumed. Thermo-mechanical and geochemical models on melt flows in volcanoes now have to be reconsidered.

• Melt Rises to Earth's Surface Up to 25 Times Faster Than Previously Assumed