More than rocks under our feet
The geological landscape shapes our daily life more than many of us realize, but most people don't contemplate it very often. Like many residents of Whitehorse, I think my water comes from a tap. I also figure Whitehorse sprang up due to traditional fishing sites, impassable rapids, a gold rush and a railway. Geologist Charlie Roots is eager to demonstrate otherwise.
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Geoscape Whitehorse is a new poster created to help residents and students interpret the city's geological landscape.
(image: Geological Survey of Canada Miscellaneous Report 82e)
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"Whitehorse is here because lava flows constricted the river," says Roots, who works for the Geological Survey of Canada and helped develop a new community poster, Geoscape Whitehorse.
"Miles Canyon and the former Whitehorse Rapids formed where the river, diverted from its former valley bottom by sediments left from the Ice Age, cut a new channel through basaltic lava," explains Roots, going back to the cause of the good fishing and troublesome rapids.
He also directs me to a corner of the Geoscape poster that depicts local groundwater systems and water and waste transport. The colourful cross-sections and diagrams offer a clear reminder that my tap water has complex origins.
Geoscape Whitehorse - Geoscience for a Yukon Community is one of a series of similar maps created for eight Canadian cities to help residents and students interpret the geological landscape. A team of local scientists, teachers and heritage advisors worked together on the Whitehorse poster to make sure the information would be accessible and useful.
"We avoided geological jargon," says Roots, "and we focused on places that are familiar to Whitehorse residents." By using simple graphics and cutaway views, map users can relate the land surface to the buried third dimension, and to changes of the landscape with time.
Measuring 1 metre high by 1.5 metres wide, the large wall poster features an aerial photo of Whitehorse surrounded by a dozen blocks of information. Simple text and catchy headings -- like 'What goes down may come back up' or 'The big chill' -- are likely to make Geoscape Whitehorse a popular resource for Yukon teachers.
Roots is keen for city residents to gain a better understanding of the geological features that surround us.
"We want to make the story of rocks and sediment more accessible," he says. "Our reports are great for scientists and prospectors, but they're not easily used by people without geological training."
"We have tried to create a public document that gives people useful information to consider when making decisions on how they use the land."
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(image: Geological Survey of Canada Miscellaneous Report 82e)
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He points out that the public needs to understand basic principles of unseen features like groundwater so they can take care of precious resources. But Roots adds that it's not just residents who are fascinated by the Yukon's geological heritage.
"Many visitors to Yukon are very interested in this kind of information. For example, some visitors to Miles Canyon look beyond the bridge and Yukon's recent history and want to know about the lava columns and why the river is there."
In the Whitehorse area, this link to the landscape is a story about fire and ice.
Roots points to the Geoscape poster and a series of graphics that depict a landscape dating back 20,000 years when a sheet of ice two kilometres thick covered most of southern Yukon. When the ice melted, parts of the Whitehorse valley were left with mounds of sand and gravel, dotted with kettle lakes, while other parts were buried beneath silt and clay deposits of left from a vast glacial lake.
Southern Yukon has twice been affected by volcanic activity. Nine million years ago lava flowed from near Mount Sima into the Yukon River valley. Another eruption created cinder cones north of Alligator Lake about 3.5 million years ago.
"We're between volcanic eruptions in this region," says Roots, suggesting that the recurrence interval might be less than six million years.
But that doesn't mean recent volcanic events haven't affected people living in the Whitehorse area. The Geoscape poster includes information about an eruption 1200 years ago -- mentioned in some native legends -- when Mount Churchill near the Alaska-Yukon border spewed gritty volcanic sand across central and southern Yukon. Known as the 'White River Ash', evidence of this eruption is a white band just beneath the soil layer.
- The Geoscape Whitehorse poster is available for $15 from the Yukon Department of Energy, Mines and Resources (Elijah Smith Bldg.) and from the Geological Survey of Canada in Vancouver and Ottawa. The poster is being provided to school science departments free of charge. Geoscape posters for other Canadian communities are posted on the Internet, at geoscape.nrcan.gc.ca.
- For information about the poster, contact the Yukon Geological Survey in Whitehorse at (867) 667-8513.
