Melt embayments and diffusion profiles to determine magma ascent rate

Quartz crystals (A) often contain melt embayments (tubular melt-filled pockets burrowed into the side of volcanic crystals) (B), which preserve volatiles (water, carbon dioxide, and sulfur) that have different concentrations in different parts of the embayment (C). The changes in concentrations within the embayments can be directly measured and modeled to infer the speed of magma as it ascended in the lead up to an eruption (D).