The curious growth of a snow crystal
Temperature and humidity affects the shape of snowflake crystals. The
temperature of formation determines the original crystal shape. Large
("dendritic") flakes grow best between -10° and -12° C. Plates grow
at warmer or colder conditions.
Humidity -- water vapor pressure in the cloud -- affects the growth rate due to deposition. A flake that passes through dry air may sublimate (lose mass by converting from solid to gas).
Because temperature and humidity change as a flake bounces around in a cloud, the basic shapes can blend into countless crystal shapes. An ice crystal may also collide with another crystal and aggregate into a snowflake of a different shape. Or crystals may grow as they accrete (collide and adhere) tiny drops of liquid water in the cloud.
More, much more, on snowflakes.
Applet and illustrations copyright (C) 2003 Tom Whittaker, S.V. Medaris, and Steve Ackerman. The Motion-W® and Bucky Badger® logos are trademarks of the University of Wisconsin-Madison.
