Two depth hoar crystals, photographed using polarized light. The width of the image is approximately 5 cm. Note that each crystal is pointed towards the top of the image and widest towards the bottom of the image. Water vapor is moving upwards, from the bottom of the image towards the top of the image. Hence the depth hoar crystals are growing downwards and INTO the source of water vapor. As each wave of water vapor condenses on the depth hoar crystal, the crystal becomes larger. The result is a very unstable crystal that acts like a lever.