Miles Canyon EarthCache
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This site is a very popular site visited by all those who travel to Whitehorse. There is little room for larger RV's to turn around so ensure you park at the top of the curve by the portable toilets
Formed by a lava flow from a now extinct volcano, this narrow canyon was a formidable obstacle for the early Stampeders who travelled to the Yukon during the Klondike Goldrush. Many lost their possessions and even their lives when they attempted to continue their travel down the Yukon River to Dawson City to discover their fortunes in gold. Near the end of the Goldrush, entrepenuers built a tram to bypass the canyon and the series of rapids for a significant cost. With the building of the hydroelectrical dam, the water deepened and tamed the water somewhat but many still experience a thrill when they canoe or kayak through the steep canyon walls.
Rocks that make up this canyon are among the youngest in southern Yukon. Several times between fifteen and nine million years ago (Pleistocene age), lava erupted quietly, as from a Hawaiian volcano, from a vent near the Mount Sima ski area in the Alligator Lake volcanic field close to Whitehorse. The lava flowed like a slow-moving river into the Yukon River valley, where it cooled to form basalt layers up to 15 m thick. Lava shrinks as it cools, forming near-vertical fractures perpendicular to the surface of the flow. Columns formed from five or six intersecting cooling fractures are a distinctive feature of many basaltic flows. The Miles Canyon Basalts is a cluster of basaltic lava flows and cones.
The Yukon River has eroded a canyon through the basalt, exposing it to view at Miles Canyon and Whitehorse Rapids. Only the top 10 meters of this layer is currently visible at the bridge. Prior to the building of the Whitehorse dam in 1959, the water level was about 10 meters lower, exposing much more of the lava.
The Yukon River generally flows through glacial deposits in this part of the Yukon. These silts, sands and gravels are soft, allowing the river to meander from side to side in the valley bottom, sometimes splitting to form braids. This meandering and braiding effect slows the river current. In comparison, the basalt rock here in the Canyon is much more resistant to lateral erosion and does not allow the river to meander. This channels the water and increases the velocity significantly.
To receive credit for this find, please email the answers to the following questions:
1. Who named the canyon and who is it named for?
2. Who is the suspension bridge that spans the canyon named after and when was it dedicated?
3. How thick is the lava flow?
Additional Hints
(Decrypt)
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