Saguenay River (Boreal shield)
Source: Lac Saint-Jean, Quebec
Mouth: St. Lawrence River at Tadoussac, Quebec
Direction of flow: east
Length: 165 kilometres from Lac Saint-Jean to Tadoussac (698 kilometres to the head of Rivière Péribonka)
Origin of name: probably from the Algonquin or Montagnais, saki, meaning “place where the water flows out”
The Saguenay is a majestic river that rises in the Laurentian Highlands, then flows through a two-kilometre wide trough in the Precambrian Shield. In places, cliffs rise 500 metres above the river. The lower Saguenay is a 250-metre-deep fjord (Canada’s most southerly) carved by glaciers of the last ice age, about 10,000 years ago. Tidewaters surge as far upriver as Chicoutimi. The Saguenay ends its course in the St. Lawrence estuary.
The deep, cold waters of the Saguenay fjord and part of the St. Lawrence estuary are rich in unusual marine life and protected as an underwater national park, the Saguenay-St. Lawrence Marine Park. Isolated populations of fish such as Greenland halibut and Arctic cod, normally found only in Arctic waters, likely survived in the Saguenay’s icy depths when the end of the last ice age warmed the surrounding waters 10,000 years ago.
Four species of whale are found at the mouth of the Saguenay: the blue (the largest animal on the planet), fin, minke and beluga. Unlike other whale species that migrate to other oceans, the beluga stays year-round in its home waters of the Saguenay fjord and the St. Lawrence estuary. It does not therefore escape the soup of chemicals concentrated in the plankton, krill and fish that make up its diet. A century ago, there were an estimated 5,000 belugas in the St. Lawrence and Saguenay systems. Today, there are only about 500. In recent years, significant conservation efforts have been undertaken to save the St. Lawrence beluga, listed as an endangered species.
The Saguenay River was once the gateway of a native trading network extending all the way to James Bay. For at least 5,500 years, aboriginal peoples met at the confluence of the Saguenay and St. Lawrence rivers to harvest fish and marine mammals. French explorer Jacques Cartier explored the mouth of the Saguenay in 1535, where he interpreted native descriptions of the river basin as the homeland of a rich and powerful people. He called it the “Kingdom of the Saguenay,” a name still in use today. The first trading post in Canada was established at Tadoussac in 1600.
The Saguenay’s wealth of water power and forest resources was not fully exploited until the 20th century. Aluminum smelters and pulp and paper factories brought prosperity to the valley, turning it into one of Quebec’s main industrial hubs. It is the most thoroughly French-speaking region of Quebec and the political stronghold for the province’s independence movement.
While paper mills and aluminum smelters ensured the economic self-sufficiency of the Saguenay region, the river paid the price of industrial development. Its waters were tainted by both industries, particularly between the 1930s and 1970s. Much of the pollution was concentrated at the mouth of the river, where sediments are contaminated with polycyclic aromatic hydrocarbons and heavy metals such as mercury. Under the St. Lawrence Action Plan, programs were initiated in the 1990s to curb industrial effluents into the Saguenay River.
Scientists have found that the disastrous flood of 1996 had a positive impact on the waters of the Saguenay and some of its tributaries. Floodwaters carried more than six million tonnes of relatively clean sediment downriver, burying chemical pollutants on the bottom of Baie des Ha!Ha! and parts of the Saguenay fjord under a blanket up to 50 centimetres thick. Researchers continue to monitor the bed of the bay and the fjord to ensure that pollutants remain permanently trapped under the new layer of sediment.
This animation shows a cross-section of the earth’s crust at the Saguenay River. As time progresses, labels, colours and arrows indicate tectonic stresses and movements. Different layers form, rise and fall.
The Saguenay fjord was created over hundreds of millions of years during the geological formation of the Canadian Shield. Successive glaciations and sea coverage has resulted in interesting stratification, sedimentation, salinity and temperature phenomena as well as extremely contrasted water depths.
Click where indicated to see how it was formed.
During the Precambrian era, the entire Saguenay region was a gigantic mountain range called the Grenville mountains. As a result of enormous pressure and high temperature, 20 to 25 kilometres of rocky mass covered the plutonic and metamorphic rock of the area. This is thought to be the beginning of the Laurentide mountain chain.
Until the end of the Precambrian era, 544 million years ago, the only landmass on Earth was a single vast continent. When it broke apart, the Canadian Shield was surrounded by ocean. At this location, the Earth’s crust underwent tremendous tectonic stress. Geological processes raised masses of anorthosite, or black granite, to the surface, which subsequently eroded.
Towards the end of the Cambrian era, the Ordovicien Ocean, located southeast of the Canadian Shield, began to close up. This contraction caused the sinking of the Shield. Consequently, the Canadian Shield was covered by a shallow warm sea in which limestone began to form. About 250 million years later, the continental fragments re-united to form one continent known as pangea.
About 200 million years ago, the breakdown of pangea resulted in the formation of the Atlantic Ocean and fragmentation into landmasses that moved against each other along various fault planes. Between a "north" fault and a "south" fault, a rock basal complex collapsed and created the Saguenay graben, a long flat-bottomed basin 250 km long and 50 km wide.
The opening up of the Atlantic Ocean led to the isolation of North America and its movement toward the North Pole. During this time, the region became significantly eroded and the layer of limestone was virtually eliminated. In the Saguenay graben, however, the limestone deposits are protected by the downward shifts caused by collapses along the fault lines.
During the quaternary epoch, 80,000 to 12,000 years ago, the climate and sea level fluctuated. The region was completely covered with a two to three kilometre thick layer of ice that moved along the rocky basal complex. The glacier rounded mountain peaks and cut deeply into the Saguenay graben, widening it in certain places, and deepening it considerably in others.
The weight of the quaternary epoch glacier was so great that it caused the gradual sinking of the region. When the glaciers melted some 10,000 years ago, the graben was consequently flooded by seawater, creating the Laflamme Sea which left behind clay deposits in the area.
After the glaciers melted and released their enormous weight, the continent gradually rose. This isostatic raising of the crust lifted the regional relief, forcing the water into the Laflamme Sea. In the Chicoutimi area, the rivers of the region carried sand and silt that eroded the former deposits and shaped the fjord valleys of today.
As a result of the raised landmass, only salt water is left in the present Saguenay fjord. This isostatic lifting of the continent has also led to the formation of step-like terraces. These are composed of clay and/or fluvio-glacial sediments.