Pam underneath mile 450 of the Trans Alaska Pipeline.  420 miles of the pipeline are above ground.  Specially designed vertical supports were placed in drilled holes or driven into the ground. In warm permafrost and other areas where heat might cause undesirable thawing, the supports contain two each, 2-inch pipes called "heat pipes," containing anhydrous ammonia, which vaporizes below ground, rises and condenses above-ground, removing ground heat whenever the ground temperature exceeds the temperature of the air. Heat is transferred through the walls of the heat pipes to aluminum radiators atop the pipes.