Editing Volcanism (section)

====Diapirs====
When material of a planetary body begins to melt, the melting first occurs in small pockets in certain high energy locations, for example [[Grain boundary |grain boundary intersections]] and where different crystals react to form [[Eutectic system|eutectic liquid]], that initially remain isolated from one another, trapped inside rock. If the [[contact angle]] of the melted material allows the melt to [[Wetting|wet]] crystal faces and run along [[Grain boundary|grain boundaries]], the melted material will accumulate into larger quantities. On the other hand, if the contact angle is greater than about 60 degrees, much more melt must form before it can separate from its parental rock. Studies of rocks on Earth suggest that melt in hot rocks quickly collects into pockets and veins that are much larger than the [[Crystallite|grain]] size, in contrast to the model of rigid melt [[percolation]]. Melt, instead of uniformly flowing out of source rock, flows out through rivulets which join to create larger veins. Under the influence of [[buoyancy]], the melt rises.<ref name=":2" /> Diapirs may also form in non-silicate bodies, playing a similar role in moving warm material towards the surface.<ref name=":3" />