There is reason to believe that the explosion was phreatic. Water in closed pores-cavities in a temperature gradient moves to the heat source for two reasons. and 1) upon dissolution of a crystalline substance in an area of elevated temperature, transfer in a liquid solution to an area of reduced temperature and deposition there. As a result, the pore-cavity moves towards the heat source. 2) the Soret effect.

Tomas Petrov