A fallstreak hole is a large gap, usually circular or elliptical, that can appear in cirrocumulus or altocumulus clouds. The holes are caused by supercooled water in the clouds suddenly evaporating or freezing, and may be triggered by passing aircraft. (also known as a holepunch cloud) forms when part of the cloud layer forms ice crystals which are large enough to fall as a 'fallstreak'. They form in clouds of supercooled water droplets, water below 0 °C but not yet frozen.