Wiktionary
melt up
vb. Of the price of a security, to increase to an unexpected degree
Usage examples of "melt up".
If not for a recent melt up-country, the release of a torrent to stir the water and keep it liquid, there might even be a treacherous skim on the river itself.
So much has been known to chemists for years, but no one yet had hit upon exactly the right flux in which to melt up the carbon, or exactly the right pressure for the best results.