Holly E. Unwin

Abstract Silicic lavas can be produced by the sintering of pyroclasts in the volcanic sub-surface, and then advected out of the vent. Here, we provide evidence for this mechanism preserved in the exposed post-glacial remnants of a silicic volcanic conduit at Hrafntinnuhryggur, Krafla volcano, Iceland.

There is a large body of textural evidence for brittle fractures in silicic magma that have healed, all while temperatures remain high14,16,24,25,32,33. In Fig. 1, we provide an example from Hrafntinnuhryggur, in Krafla, Iceland (photo taken by Jenny Schauroth). Other examples have been documented in the products of both dominantly effusive11,17, and mixed explosive-effusive24 silicic eruptions. These healed, or partially healed, fractures often contain welded fragments9,34.