Definition of "unfrozen"

In getting out of this I found it easier to wade down a shallow unfrozen stream than to wallow through deep snow.

1915 April, Enos A. Mills, “In the Winter Snows”, in The Rocky Mountain Wonderland, Houghton Mifflin, page 259

One would assume that here the chief problem would be to keep the conductor rails and point mechanisms unfrozen.

1962 March, “Lessons of the Freeze-up”, in Modern Railways, page 145