Railway tracks stretch across long distances in open field locations where hauling in a bulky welding machine or a stable electrical power supply is simply not practical. Thermit welding gets around this problem entirely by relying on a self-sustaining chemical reaction, aluminium powder reacting with iron oxide, which on its own releases enough heat to melt steel and produce a superheated liquid that is poured directly into the gap between two rail ends. Once this molten steel cools and solidifies, it forms one continuous joint as strong as the rail itself. Since the process needs no external electricity and works reliably on thick rail sections out in the field, thermit welding is the standard method used for joining railway tracks.