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Does the Lake Freeze Over? 

ONCE IS A LIFETIME (Crater Lake froze over in 1924 and 1949)

The answer to the question about why Crater Lake rarely freezes

completely over, even when it gets very cold, has to do with two

factors

(1) The extreme depth of the lake, which stores the heat input

from the summer,

(2) The high winter winds, which provide the important energy

needed to mix the colder but less dense waters at the surface with

the more abundant, deeper, slightly warmer, and more dense water

of the lake.

In the winter, in the absence of wind, the lesser dense cold water

near freezing rises to the surface and the more dense surface water

at 38 to 39 degrees F. (3.5 to 4 degrees C) sinks towards the

bottom of the lake.

Scientific studies show that below a depth of about 820 feet (250

meters), most of the lake’s water remains at a temperature near

38.3 degrees F (3.5 degrees Celsius) all year round. During the

winter, the top 330 feet (100 meters) remains at a temperature

near 37 degrees F. (2.7 degrees C).

All it will take is one very cold windless night, and the lake will

begin to freeze. If it snows the next morning, or if it’s cloudy

without sun, the ice will continue to form, provided that there’s

no wind or that a veneer of ice has completely covered the lake,

eliminating wind as a factor.

Otherwise, in the presence of direct sunlight, the clear thin ice

layer will act like a lens. Penetrating sunlight will warm the water

underneath the ice, causing the thin layer of ice to melt from below.

If a layer of snow covers the ice, the sun will have little effect

on the water below the ice, and as long as it remains cold, ice will

continue to form.

However, as long as the ice does not cover the entire surface of

the lake and water is exposed to the air, the wind will do its part

to keep mixing warmer deeper water with the colder water of the

lake’s surface to prevent more ice from forming, and melting any

remaining ice.