1977’s The Ice is Coming is the first volume in Patricia Wrightson’s Wirrun trilogy.
The Ninya, the ice folk who live unnoticed beneath Australia, have a dream: to return to the surface world, freeze it solid, and then be free to roam. Only the Eldest Nargun, a volcanic rock creature that can summon fire, could confound the Ninya. If the Ninya act quickly, by the time their ancient enemy learns what the Ninya are up to, it will be too late.
Unfortunately for the simple ice folk, they boldly discuss their vision unaware that someone is eavesdropping.