| How to melt mantle rock |
The region of the planet that is responsible for providing the melt needed to initiate volcanic eruption is the mantle. While pop-culture may think that the mantle is molten in nature, in reality it is nearly 100% solid. There are three ways to melt mantle rock (after Asimow, 2000):
Raise the Temperature: While this may seem the most obvious way to induce melting of mantle material, this method by far is the least common of the three. Lower the pressure: This is the most common way to melt mantle material. If we have a region of solid mantle moving closer to the surface in an isothermal fashon, then the pressure becomes lower; thus we can promote melting by reducing the confining inter-moleculear pressure. Change Chemical Composition: The addition of different chemicals from outside a magmatic system (mainly volitiles (gasses)) to a gassless melt can cause the the mantle system to lower its point of initial melting (or lower its liquidus). One famous volitile is water, which upon its introduction to a segment of mantle, usulally along subduction zones, acts to break up the chemical bonds that exist in the then-solid mantle material and thus promote melting. |