What word has w for a vowel?

No, it isn't.

no

actually I seem to recall a geological term of Scandinavian derivation GWM refering to a glacial lake.

You may be thinking of an acronym. GWM can stand for Ground Water Management or Monitoring. You may be right, but a hasty search doesn't support it.

But the Word cwm (pronounced coom to rhyme with loom) has been imported from Welsh to mean a hollow at the head of a mountain valley. In this case the w is a vowel.