![]() ![]() In places the slopes are incised with deep gullies due to erosion. It ranges from relatively flat in the north to steeper slopes in the south along the creek’s banks. The topography varies considerably in Larch’s Sanctuary’s stretch of Whitemud Creek. It is composed of sandstone, clay shale and numerous coal seams. Below this mix of silt and clay there is glacial till, then the bedrock of the Horseshoe Canyon formation. The Palliser Expedition named it for the white-coloured mud that settled out when Lake Edmonton covered the area. Whitemud Creek is a tributary of the North Saskatchewan River. Erosion then formed the Edmonton River Valley system we see today. Water flowing over the old glacial lakebed eventually established a preferred channel. ![]() Imagine huge flows moving several thousand cubic kilos of rock and sediment! The flood set the stage for the appearance of the North Saskatchewan River. One theory suggests the flood lasted only a few weeks. “The force of the flow ate at the ice above and the ground below, rapidly enlarging this sub glacial drain until, in a torrent of water and ice and rocks and soil, the lake poured out of its icy basin and into the Battle River, carving a deep channel as it went.” ( B. Water found a low point under the dam and began to flow south. When the lake disappeared, it did so in a flash of geological time. Water covered the area from Morinville to Leduc, from Stony Plain to Fort Saskatchewan. For almost 100 years, “Lake Edmonton” was walled in on three sides by sheets of ice. The Dramatic Break Up of Lake EdmontonĪs the thick ice sheet began to melt, a gigantic ice dam trapped the water. The last of four major glacial advances of ice buried Edmonton under an ice sheet more than 1 km deep. Glaciers flowed down to the plains of Western Canada. Roughly one million years ago, the Arctic ice cap began to grow. Bison, muskox, horses, woolly mammoths and mastodons wandered the grasslands and the thin boreal scrub bush. Tropical vegetation gave way to grasses and sedges better suited to a northern environment. As the North America Plate continued to move north, the seasonal lack of direct sunlight caused the extinction of many animals. Lush forests thrived due to abundant rainfall and the fertilizing effect of volcanic ash. Later, in the Mesozoic Era, the land cooled as continental drift moved Alberta into more northerly latitudes. This is the source of our vast oil and gas reserves. Gradually, thick deposits of organic materials accumulated and were buried on the ocean floor. The fossils from this time suggest the land was covered by a flourishing tropical sea. During this era continental drift took Alberta to a warm, sunny location somewhere between latitudes 30° north and 30° south. One of the oldest layers is likely the massively eroded Precambrian margin of the Canadian Shield. Edmonton sits on strata deposited by various geological processes. ![]()
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