Slate Islands (Ontario)
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The Slate Islands archipelago is formed of two main islands, five minor islands and numerous islets located in northern Lake Superior, 10 km (6.2 mi) south of the town of Terrace Bay. The islands were created by a meteorite impact which formed a crater about 32 km (19.9 mi) wide.[1] In 1985, the Ontario government established the Slate Islands as a natural environment provincial park. The islands are notable for having Ontario's largest herd of woodland caribou.[2]
The total surface area is about 36 km². The nearby 'Leadman Group' of islands one km east is often considered part of the Slate Islands.
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[edit] Flora
The cooling effect of Lake Superior make the Slate Islands a particularly harsh habitat for its latitude. As a result, islands harbour arctic and alpine plant species such as Dryas Drumondii and Alpine Bistort, the latter of which is an Inuit delicacy eaten with seal oil.[3] These arctic disjunts are reminders of ice ages and associated tundra conditions in this area in the past.
[edit] Fauna
The islands are home to woodland caribou which have been studied extensively from 1974 to today by Dr. A.T. (Tom) Bergerud. The caribou are a classic example of island biogeography in action; the islands are notable for species that are absent but present on the adjacent mainland (red squirrel, moose, white-tailed deer, and grouse). No ungulates were present on the islands until the caribou arrived in the early 1900s. And, no predators of caribou were present. Caribou reached and maintain higher density than anyplace in the world here. Wolves reached the archipelago in the early 1990's preying heavily on the caribou but for reasons not entirely known they disappeared a few years later. Other mammals found on the islands include beaver, muskrat, snowshoe hare, short-tailed weasel, red-backed vole, and red fox.
The waters surrounding the Slate Islands have been protected from commercial fishing to preserve one of the last native stocks of lake trout in Lake Superior. The Islands have been a source of lake trout brood stock used at the Dorion Fish Hatchery, and fingerlings are planted back to Lake Superior to restore the fishery.
[edit] Human History
Human sites have been found on the islands dating to about 1000 A.D.[4]
A lighthouse was built on Patterson Island, the largest island, in 1903 to help ships locate the harbour at the nearby town of Jackfish, Ontario. The island is named after William Patterson, a former lieutenant-governor of Saskatchewan. Later, a fishing station was built on McColl Island.
The original forests on the islands were modified by logging and forest fires. Up until the 1940s, the islands were used to stockpile boomed logs from the mainland Lake Superior north shore for export on lake freighters to pulp mills in the United States.
In 1985, the Slate Islands were protected as an Ontario provincial park. There are no facilities and the islands can only be accessed via boat or airplane. The islands remoteness is enforced by almost 9 km of open, wild, Lake Superior water and its distance from any large communities. It is frequented by naturalists, fishing parties, sailors exploring this Great Lake, and recently by an increasing number of sea kayaking parties.
[edit] Geology
The Slate Islands mark the centre of a large meteorite impact crater. The original crater rim is estimated at about 32 km (19.9 miles) in diameter, but this and most of the crater has subsequently eroded away, leaving the islands which are interpreted as a central uplift. The age of the impact event is estimated to be about 450 million years (Ordovician).[5] Another source estimates the age at 800-500 million years (late Proterozoic to early Paleozoic).[6] The islands are not made of slate; the rock is mainly of volcanic and sedimentary origin.[7] Allogenic breccia is present, notably on the east and north sides of the islands.
[edit] Notes
- ^ Sharpton, V.L. and Dressler, B.O. 'The Slate Islands Impact Structure: Structural Interpretation and Age Constraints', Lunar and Planetary Science. March 1996: vol. 27, page 1177
- ^ Chisholm, B. and Gutsche, A., Superior: Under the Shadow of the Gods, Lynx Images, 1998, p. 180
- ^ Chisholm et. al., ibid, p. 180
- ^ Chisholm and Gutsche, ibid, p. 178
- ^ ILSG Slate Islands trip. Retrieved on 2008-03-30.
- ^ Sharpton, V.L. and Dressler, B.O. ibid, p. 1178
- ^ Ontario Parks website. Retrieved on 2008-03-30.
[edit] References
- Chisholm, B. and Gutsche, A. (1998). Superior: Under the Shadow of the Gods, Toronto: Lynx Images. ISBN 0-9698427-7-5
[edit] External links
- Slate Islands at Earth Impact Database
- Aerial Exploration of the Slate Islands Structure
- Slate Islands, Ontario Parks
- Slate Islands Provincial Park, Terrace Bay, Ontario
