Why does salt on snow create Ice?

Question

I think I kind of understand this process but I would like someone to explain it more completely.

For those who aren't aware here is the scenario I'm talking about:

As terrain maintenance at my local ski slope we often use salt to firm the snow around jumps on warm slushy days. Throwing down a even layer of salt causes the snow to become firm and icy on its top layer (thus causing jumps to hold up better during heavy use).

My best guess to this phenomena is that the latent heat of vaporization in the melting of some of the snow causes the snow below to become colder. As the snow on top melts it sinks down leaving an icy layer on top.

Am I on the right track? or is something else going on?

Answer 1

Salt lowers the melting point of water. When you throw it on snow (in not-too-cold weather), it causes some of the snow to melt, and the snow surrounding it will melt until the concentration of salt is low enough that the melting point of the salt water is above the ambient temperature. This will form a layer of ice. You can achieve roughly the same effect with a hair dryer.