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A legacy of fire and ice

Volcanoes of the Garibaldi Belt add dramatic scenery to Whistler's mountain landscape

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If you know exactly where to look from the top of Whistler, the circular mound of Ring Mountain can be seen tucked in among the older peaks and at its base is a beautiful clear lake surrounded by flower-filled meadows. It’s a long day hike in from the Callaghan road but the campsite is worth every step of the way. With its pronounced southerly list Ring Mountain resembles a giant baking failure, a fallen souffle. Its circular form, flat top, and steep sides are characteristic of tuyas but the thick, southerly sloping cap that gives the 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 tuya surrounded by a moat of glacial 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.

Not all the lava that issued from ice-covered vents made it to the surface. According to Bill Mathews the sinuous ridges of columnar basalt at the south end of Daisy Lake and around the B.C. Rail quarry were formed where lava was confined to meltwater channels beneath the ice. And in the Cheakamus River valley, near the demonstration forest, Logger’s Lake now occupies the crater of a small andesitic volcano that was born and died beneath a kilometre of glacier ice. Next time you're biking along the Cheakamus Lake road take the time to pause at Crater Lookout or, better still, hike around the crater of this relic of the ice age.

The Cheakamus Valley volcano is a typical "sub-glacial mound," a blister of molten lava that was large enough to thaw a large cavity beneath the ice but not massive enough to melt an open pit – a sort of failed tuya that never developed discrete flows or the classic flat top. Its extremely long columns, formed by shrinkage during cooling, suggest that the Cheakamus lava cooled from a single large mass. Any loose pyroclastic bombs or blocks that may once have mantled it were swept away by the very ice that encased it. The remaining core of resistant andesite is deeply scoured by ice and the surface of the dome is strewn with glacial eratics, abandoned during the final withdrawal of the glacier.

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