Abstract

Howe Lake (formerly called "Goudie Lake") is an unusual feature of southeast Saskatchewan. Almost perfectly circular (diameter 295 m), it is much deeper (26 m) than almost any other prairie lake. Initially noted in 1952, numerous investigations culminated in deep drilling and geophysical programs in the 1969–1976 period. The lake is the surface expression of a deep, funnel-shaped depression filled with coarse colluvium at the bottom and finer material near the top. A central pipe extends to a depth of at least 138 m. Radiocarbon dates and the history of deglaciation give evidence that the structure was formed between 12 000 and 12 500 years BP, shortly after the last ice sheet melted in the area. The structure was probably formed by a hydrodynamic blowout of water from the Mannville Group 400 m below surface. Extreme overpressure of water in the Mannville Group was probably induced by recharge from meltwater of the continental glacier then standing a few kilometres to the north of Howe Lake. The blowout was initiated at Howe Lake by fractures in the subsurface, related to a salt solution-collapse structure. Howe Lake probably served as a valve controlling the artesian pressure in the Mannville Group over a large area, until the active ice margin had retreated northeastward exposing lower elevation discharge areas. Hydrodynamic blowouts provide another process for the origin of breccia-filled pipes.

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