If you know exactly where to look you can see it from either Whistler or Blackcomb. Crucible Dome, known locally as "Ring Mountain", is not a particularly imposing landmark. Nestled into an obscure valley north of the Powder Mountain ice field it resembles a petrified baking failure, a fallen soufflé, perfectly round but listing badly. But for those of us who have an empathy for volcanoes of all shapes and sizes Ring Mountain is indeed special among our local hills.
I first learned about sub-glacial volcanoes from Bill Mathews, my U.B.C. geology professor and mentor, who showed us his slides of the classic "Table Mountains" of Iceland and described how they were formed. How lava erupted from a vent under the ice had thawed a pit and, unable to flow away, had piled up within the depression. He later identified similar flat-topped, steep-sided piles of lava on the Tuya Plateau in northern B.C. and published a paper in which he called them "Tuyas". The name stuck.
Many years later, when I was studying the volcanoes of the central Garibaldi Belt, I discovered that Ring Mountain and several of its neighbours were clearly the result of sub-glacial eruptions. They must have formed when the Cordilleran Ice Sheet was near its maximum between one million and 12,000 years ago when glacier ice periodically filled the valleys of the southern Coast Mountains.
The circular form, flat top, and steep sides of Ring Mountain are characteristic of tuyas; and lavas in its lower part show evidence of quenching by water or ice. But the thick, southerly sloping cap flow that gives Ring Mountain its skewed profile is a typical dry-land lava flow whose upper surface is strewn with bombs and coarse ash. It seems that Ring Mountain began its life as a mound of quenched lava under thick ice cover. As it grew larger it was surrounded by a moat-like depression filled with meltwater. At some point the enclosing ice dam gave way, draining the lake and leaving the newly-formed tuya high and dry. The final massive flows of viscous lava issued along its northern rim and spread out across its dry surface while bombs and ash rained down from a fire fountain at the vent.
But my memory of working on Ring Mountain is much more than just rocks. We camped on the shore of a small, pristine lake near the southeastern flank of the dome. Each day's climb started with a walk through meadows crowded with alpine flowers and ended with a dip in the lake. And each day revealed new clues and new mysteries about the way ice and lava combined to shape part of our recent geological past. While Betty and I had the luxury of a helicopter, the place we camped is a modest eight kilometre back-pack from the head of the Callaghan Lake road. Whatever your interest in the mountains – geology, wildlife, or just getting away from it all – Ring Mountain is an alpine destination worth every bush-whacking step of the hike or ski in.
Written by: Jack Souther