The porous rock soaks up moisture, degrading the limestone.

But the coroner jokingly reminded the jury that he was 'quite a porous rock' - considering the amount of her secrets that were leaked.

Inside the volcano, they contend, that seepage raised the pressure of groundwater held within the porous rock to its highest levels in a half-century.

Once separated, the gas can be stored in geological structures, either dissolved in water, held in porous rock or trapped under a layer of rock it cannot permeate.

These can be formed from molten droplets originating from meteor impacts or from volcanic action, or they can precipitate from solution inside of porous rock.