If we assume a sim- ilar value for magma emplaced beneath Alcedo, between 0.6 and 10% of the magma would need to crystallize each year, to give the model distribution of volume reduction at 95% confidence. Note that the probability distribution for percentage of crystallization is less well constrained than that for volume reduction, as it also de- pends on the total volume which is not so well constrained. Cooling of the solidified magma could also contribute further to the volume reduction, with up to 2% contraction being the estimated value for solidified Krafla magma. Loss of volatiles from the magma chamber would reduce the pressure, also leading to a reduction in volume, but the pressure decrease required to produce the surface displacements

would be between 23 and 370 MPa yr−1 at 95% confidence. This range is too high to be plausibly produced by the loss of volatiles alone. Ref 1