Tuesday, October 19, 2010

Pic Today 10/19/10


Throughout the southern Missouri Ozarks,
"frost flowers" form on the stems of ironweed in the fall.
The formation of these exquisite paper-thin ice crystals
occurs when the temperature of the air falls below freezing,
but when the ground is not already frozen.

The sap in the stem of the plants will expand
(water expands when frozen)
causing long, thin cracks to form
along the stem near the ground.
Water is then drawn through these cracks
via capillary action and freezes upon contact with the air.
As more water is drawn through the cracks,
it pushes thin ice layers further from the stem
causing "petals" to form.

These beautiful and delicate "frost flowers"
usually melt when the sun's first rays appear,
and are only visible in the early morning.
(Frost flowers don't bloom in the winter.)

There is a current exhibit of Ozark "frost flower" photographs
on display at Missouri Botanical Garden, St. Louis.

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