Iodine monoxide, IO, is observed in satellite measurements following the eruption of the Kasatochi volcano, Alaska, in August 2008. Large IO columns are detected by SCIAMACHY on ENVISAT and by GOME-2 on MetOp-A for several days. IO amounts are approximately 1 order of magnitude smaller than those of BrO. Details in the spatial distributions differ between IO, BrO and sulfur dioxide, SO2
. The total mass of IO in the volcanic plume is determined to be on the order of 10 Mg.