Figure A10. Helmcken Falls Wells Gray Park owes its origin to the 142 m free-falling Helmcken Falls. The Helmcken Falls owe their origin to numerous lava flows that filled up the ancient channel of the Murtle River. At the end of the last ice age, massive floods from the melting ice carved a deep canyon into the underlying lava flows and formed Helmcken Falls. The face of the basaltic flows and falls remains vertical due to the nature of the basaltic flows. Basaltic lava shrinks as it cools and forms vertical columns. Rows of columns peal of the cliff face like slices of bread, preserving the vertical nature of the cliff. (Photograph by C.J. Hickson (Geological Survey of Canada)) larger image [JPEG, 26.4 kb, 264 X 390, notice]

The Wells Gray region of east-central British Columbia is a volcanic field made up of numerous, small, basaltic volcanoes. Individual volcanoes have been active for at least the last 3 million years during which time the region was covered by thick glacial ice at least twice, prior to the well known Fraser Glaciation (also known as the 'Wisconsin Glaciation'). Volcanic eruptions underneath and through the thick blankets of glacial ice produced numerous unique glacial volcanoes and deposits, including one explosive, subaqueous volcano, five tuyas, at least one subglacial mound, and numerous, thick, valley-filling deposits of volcanic rocks. Between the periods of glaciation, the volcanoes continued to erupt and filled river valleys with many layers of basaltic lava flows. The valley-filling flows, now incised by rivers, have created a unique landscape of steep, narrow valleys and numerous waterfalls. A particularly beautiful waterfall is the 142 m (465 ft.) high, free-falling Helmcken Falls (Figure A10). Its beauty and that of the surrounding area prompted the provincial government to set the area aside as a park in 1939.

Figure A11. Dragon Cone Dragon cone is the source of the 15 km long Dragon's tongue lava flow that dams Clearwater Lake. The cone, made up of cinders, blocks, and bombs, is perched on the side of a ridge of metamorphic rock. (Photograph by C.J. Hickson (Geological Survey of Canada)) larger image [JPEG, 26.6 kb, 400 X 266, notice]

A single road enters the park, but from it, a number of the park's volcanic features can be viewed. Short hikes lead to several spectacular volcanic features. The road terminates at the southern end of Clearwater Lake, where a short hike up the Kostal Lake trail leads to the Dragon's tongue lava flow (Figure A11). The flow, which is now punctuated by tree moulds visible from the trail, travelled 15 km from the vent. It forms a 3 m high dam across the southern end of Clearwater Lake, which maintains the existing lake level. This flow is just one of the examples of volcanic activity that have occurred in the region since the last ice age. This activity involved small fire-fountaining eruptions that produced cinder cones and lava flows. Other cones in the area include Kostal cone (at a few hundred years old, it is most likely the youngest in the region), Flourmill cone, and Spanish cones. Some lava flows at Wells Gray Park are unique in that they contain small, angular to rounded fragments of rock (called 'nodules') and crystals that come from the mantle below the Earth's crust. These green nodules are called 'peridotites' because they are composed predominantly of the mineral olivine (the gem form of which is known as 'peridot'). These lavas also contain large crystals of olivine, plagioclase, and pyroxene that crystallized deep within the Earth's crust and mantle. The lavas and the nodules they contain are similar to those erupted in the Volcano Mountain area of the Yukon Territory. The nodules help scientists determine what the mantle below the volcano is like.

Figure A12. Pyramid Mountain Pyramid Mountain, once mistaken for a cinder cone, is now known to have formed below several thousand metres of glacial ice. Hemmed in by the surrounding ice, the volcano erupted vigorously, creating layers of glassy, but vesicular, scoria intermixed with smoothed cobbles of granite and metamorphic rock. These rocks were picked up by a glacier many kilometres away and melted out of the ice because of heat from the volcano. Although it had a vigorous start, the eruption that formed Pyramid Mountain was not sufficiently sustained to form a larger edifice that could break through the surrounding ice and water to form a tuya. (Photograph by C.J. Hickson (Geological Survey of Canada)) larger image [JPEG, 14.5 kb, 400 X 262, notice]

A viewing platform on Green Mountain in the southern part of the park affords views of a number of the park's tuyas including McLeod Hill, Mosquito Mound, and Pyramid Mountain. McLeod Hill and Mosquito Mound are prominent, flat-topped, steep-sided volcanoes with a typical tuya shape (see Figure 23, stage 3b). Pyramid Mountain (Figure A12), with its pyramidal shape, is a subglacial mound that never broke through the overlying ice cap (see Figure 23, stage 2b).

Figure A13. White Horse Bluff White Horse Bluff is a deceptive volcano. Only a trained eye can pick out the yellow-weathering hyaloclastite and recognize that this is indeed a volcano. Formed by repeated subaqueous explosions, the volcano eventually built up above the water level. It was fed by dykes (dark areas on the cliff face) cutting through the hyaloclastite and ceased erupting soon after breeching the surface of the water. (Photograph by C.J. Hickson (Geological Survey of Canada)) larger image [JPEG, 21.0 kb, 400 X 261, notice]

White Horse Bluff, another distinctive subglacial volcano at Wells Gray Park, has a most unvolcano-like form (Figure A13). The bluff is an eroded remnant that marks the place of a violent eruption, thought to have involved the following sequence of events: 1) water, likely dammed by glacial ice, filled the Clearwater River valley; 2) the water flooded down the volcano's vent, producing large explosions of steam and broken lava fragments; 3) once the explosions had subsided, these fragments settled back into the water, building up a volcano composed almost entirely of fragmental volcanic glass (hyaloclastite).

Wells Gray Park has had a long history of relatively quiet fire-fountaining-style eruptions. More violent explosions are possible only in unique circumstances, such as an eruption into a lake. Any future eruption is most likely to affect only a limited area downslope from the volcano. Poisonous gases could be expelled and, as the flows are likely to travel long distances, it is conceivable that drainage systems could be rearranged and some river valleys might be dammed. Lava flows could start forest fires as most of the region is wooded. Salmon do not swim very far into the park, but future eruptions could have an impact on the significant recreational trout fishery in the park's lakes and river. Disruption of local air traffic and tourism is possible and could represent a crowd-control hazard in this remote yet relatively accessible region.