Lenticular clouds. Stack of lenticular clouds, named for their smooth lens-like shape, seen over a mountain. Lenticular clouds often occur in vertical piles or stacks as here. They are produced when moist air ascends over a mountain, and air waves form on the lee side of the mountain. As the wind rises and moisture is present in the air lenticular clouds rise up. If alternate layers of moist and dry air are present, the clouds form into a stack. Photographed over the Mauna Kea volcano, Hawaii, from Waimea, after a storm on 29 December 1996. The summit of Mauna Kea is 4205 metres above sea level.