A fallstreak hole, or hole punch cloud, in altocumulus clouds. Supercooled water droplets in the centre of this cloud have turned to ice, perhaps as a result of an aircraft's passage through the cloud. As the ice crystals grow they fall to a lower altitude, leaving a hole in the cloud. The freezing effect ripples outwards expanding the hole. The iridescence effects around the edge of the hole indicate that the remaining cloud is composed of supercooled water and not ice.