Clearwater Lakes

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Clearwater Lakes
Lac à l'Eau Claire
STS61A Clearwater Lakes.jpg
Clearwater Lakes as seen from a Space Shuttle (North is top right)
Location Baie-d'Hudson, Kativik, Quebec
Coordinates 56°08′N 74°18′W / 56.133°N 74.300°W / 56.133; -74.300Coordinates: 56°08′N 74°18′W / 56.133°N 74.300°W / 56.133; -74.300
Type impact crater lake
Primary outflows Clearwater River
Basin countries Canada
Surface area 1,383 km2 (534 sq mi) [1]
Max. depth 178 m (584 ft) [2]
Surface elevation 241 m (791 ft) [1]
Clearwater Lakes, 2013 image by NASA Earth Observatory

The Lac à l'Eau Claire (the official name, in French), also called the Clearwater Lakes in English, Wiyasakami in Cree and Allait Qasigialingat by the Inuit,[3] are a pair of annular lakes on the Canadian Shield in Quebec, Canada, near Hudson Bay.

The lakes are actually a single body of water with a sprinkling of islands forming a "dotted line" between the eastern and western parts. The name is due to the clear water it holds. There are actually 25 lakes with that name in the province (26 if the Petit lac à l'Eau Claire — the Small Clearwater Lake — is included). These are the largest and northernmost, and the second largest natural lake in Quebec after Lake Mistassini.[2]

In 1896, the explorer and geologist Albert Peter Low, a member of the Geological Survey of Canada, provided the probable origin of the lakes' descriptive name by highlighting the extraordinary clarity and depth of their icy waters.[3]

Impact craters[edit]

The Clearwater Lakes occupy the near-circular depressions of two eroded impact craters (astroblemes).[4] The eastern and western craters are 26 km (16 mi) and 36 km (22 mi) in diameter, respectively.[5][6] Both craters were previously believed to have the same age, 290 ± 20 million years,[7] promoting the long held idea that they formed simultaneously. According to this doublet impact crater theory initially proposed by Michael R. Dence and colleagues in 1965,[8] the impactors may have been gravitationally bound as a binary asteroid, a suggestion also made by Thomas Wm. Hamilton in a 1978 letter to Sky & Telescope magazine in support of the then-controversial theory that asteroids may possess moons (such as, for example, asteroid 243 Ida with its satellite Dactyl[9]). However, repeated 40Ar/39Ar dating of impact melt rocks from both impact craters suggests that Clearwater East has an age of approximately 460–470 million years, corresponding to the Ordovician time period, whereas Clearwater West was formed 286.2 ± 2.6 million years ago, in the early Permian.[10][11] Both Clearwater impact structures also carry different geophysical (natural remanent magnetization) signatures[12] and different geochemical fingerprints of the impacting meteorite in the impact melt of each crater.[13]

Clearwater East and Clearwater West are both complex craters with distinct central peaks. These peaks are caused by the gravitational collapse of crater walls and subsequent rebound of the compressed crater floor. Lake water and sediments cover the central peak of Clearwater East, but bathymetric surveys of the lake floor and core drilling confirm the presence of a peak in its center.[14]

Micro climate[edit]

Because of its size, Lac à l'Eau Claire can affect the local climate, as attested to by the distribution of plant species. Although the lake's shorelines are populated mainly by boreal species, the flora of the central islands in the western basin of the lake is characteristically arctic, making the islands an arctic enclave.[2]

National park[edit]

A vast area surrounding the lakes, Richmond Gulf (Lac Guillaume-Delisle), and Iberville Lake (Lac D'Iberville) are part of the 15,549 km2 (6,004 sq mi) Tursujuq National Park, Quebec's largest national park, opened in 2012.[2]

References[edit]

  1. ^ a b Statistics Canada > summary tables > Principal lakes, elevation and area, by provinces and territories
  2. ^ a b c d Ministère du Développement durable, de l'Environnement et des Parcs, Provisional Master Plan Parc national des Lacs-Guillaume-Delisle-et-à-l'Eau-Claire, Quebec, 2008, ISBN 978-2-550-52710-7 (Online version)
  3. ^ a b "Lac à l'Eau Claire" (in French). Commission de Toponymie Québec. Retrieved 2009-01-30. 
  4. ^ Robertson, P.B. & Grieve, R.A.F. 1975 Impact structures in Canada: Their recognition and characteristics. Journal of the Royal Astronomical Society of Canada, v. 69, pp. 1-21.
  5. ^ "Clearwater West". Earth Impact Database. University of New Brunswick. Retrieved 2008-12-30. 
  6. ^ "Clearwater East". Earth Impact Database. University of New Brunswick. Retrieved 2008-12-30. 
  7. ^ Reimold, W.U., Grieve, R.A.F. and Palme, H. 1981. Rb-Sr dating of the impact melt from East Clearwater, Quebec. Contrib. Mineral. Petrol. 76, 73–76.
  8. ^ Dence, M. R., Innes, M. J. S. and Beals, C. S., 1965. On the probable meteorite origin of the Clearwater Lakes, Quebec. Royal Astronom. Soc. Canada J. 59, 13–22.
  9. ^ Chapman, C.R., Veverka, J., Thomas, P.C., Klaasen, K., Belton, M.J.S., Harch, A., McEwen, A., Johnson, T.V., Helfenstein, P., Davies, M.E., Merline, W.J., Denk, T., 1995. Discovery and physical properties of Dactyl, a satellite of asteroid 243 Ida. Nature, 374, 783–784.
  10. ^ Bottomley, R.J., York, D., and Grieve, R.A.F. 1990. 40Argon-39Argon dating of impact craters. Proc. 20th Lunar Planet. Sci. Conf., LPI, Houston, pp. 421–431.
  11. ^ Schmieder, M., Schwarz, W. H., Trieloff, M., Tohver, E., Buchner, E., Hopp, J. & Osinski, G. R. 2014. New 40Ar/39Ar dating of the Clearwater Lake impact structures (Québec, Canada) – Not the binary asteroid impact it seems? Geochim. Cosmochim. Acta (in press).
  12. ^ Scott, R. G., Pilkington, M. and Tanczyk, E. I. 1997. Magnetic investigations of the West Hawk, Deep Bay, and Clearwater impact structures, Canada. Meteoritics Planet. Sci. 32, 293–308.
  13. ^ Palme, H., Janssens, M.-J., Takahashi, H., Anders, E. and Hertogen, J. 1978. Meteoritic material at five large impact craters. Geochim. Cosmochim. Acta 42, 313–323.
  14. ^ A One-Two Punch by NASA Earth Observatory

External links[edit]