A Winter Conundrum - climbing salt

[WhatReally]

Per photo, snow and salt melted off my boots treads seems to have "climbed" out the the tray where I keep them. I find this absolutely bizarre.
Any thoughts?

 

[Borek]

Nice one.

Probably some combination of temperature gradient, air movement drying the salt, tray surface hydrophobicity/hydrophilicity and a wicking effect of the salt that already crystallized. Not that I have a quick and obvious idea about details, but it might be quite non trivial and depend on very particular position of the tray near a heater, vent and so on.

 

[WhatReally]

Makes sense. Thanks!