The Historical Grand Rapids of the Athabasca River
The Grand Rapids are on the Athabasca River between Athabasca and Fort McMurray. The rapids are formed by huge boulders that stretch across the river from bank to bank creating a major transportation hazard and a striking geological feature. During the fur trade, the Athabasca River became the Hudson's Bay Company's main river route to the north and the notorious Grand Rapids were the greatest obstacle on it. The rapids are still remote today and can be approached only by boat or aircraft. Because the isolation of this area and the difficulty of the rapids, a canoe tour should be attempted only by the most experienced canoeists. The Grand Rapids are impassable at any water level and have claimed the lives of a number of unsuspecting and ill-prepared canoeists.
Travelling the historic boat route down the Athabasca River from Athabasca (formerly called Athabasca Landing) to Grand Rapids, one reaches the tiny settlement of Pelican Portage, about 75 kilometres above the rapids. This was the site of a 19th-century gas well blowout that burned out of control for 21 years producing a bright, wild beacon to river traffic. The first sign of the Grand Rapids comes five kilometres upstream where you can begin to hear the roar of the rapids. At the rapids, 253 kilometres downstream of Athabasca Landing, a large island separates the river into an east channel and a more dangerous west channel. The rapids run for 1.6 kilometres dropping over 11 metres in the first kilometre over a sloping boulder dam.
The rapids are a result of river erosion of the 110-million-year old sandstone of the Grand Rapids Formation. This formation, which forms the large, nearly vertical outcrop on the east side of the valley, is divided into three major sandstone layers. The lowermost level creates the rapids because it is filled with large, two-to-three metre wide, concretions that often contain pieces of petrified logs. These concretions were formed in a similar fashion to those at Red Rock Coulee. As the river erodes away the sand matrix, these huge concretions come loose and dam the river bed.
West of this region, in the Wabasca Lakes area, the Grand Rapids Formation is well known as a subsurface oil sand deposit. The oil is found in the upper two layers of the formation while there is no oil in the lower boulder-rich layer that is responsible for the rapids.
Reprinted from A Traveller's Guide to Geological Wonders in Alberta by Ron Mussieux and Marilyn Nelson with permission of the authors and the Provincial Museum of Alberta.