Jack Vance-esque fantasy, 2000s-ish published, MC great at climbing
I'm sure I read a fantasy book in the 2000s, that had a very Jack Vance-esque style: mages had to build up power through multiple days of meditation, they have different magical affinities.
Early on in the book, two mages are walking through torrential rain. The senior mage (sort of a fire mage?) is soaking; the junior mage is wisely wearing oiled cloaks and is basically dry. A dragon (?) attacks, and the lead mage wastes all their power firing a bolt of mage into the sky; it "boils a few rain drops". The junior mage has the talent to talk to rocks - they reawaken a volcanic trench and bring it down.
Later it matters that one of the main characters is a great climber - they might have been the bad guy? They climb up to a fortress or tower quickly and unexpectedly.
I think in the same book, a mountain gets turned to dust. The protagonist has to run like heck to avoid the dust avalanche suffocating them.
I remember really liking the book, and wanting to read sequels. Any help hugely appreciated!