St. Lawrence Lowlands

The St. Lawrence Lowlands region is a geographical area of the Canadian province of Quebec that sits in a large, flat basin, extending from the Saint-Lawrence River and its estuary near Quebec City in the east to Longueuil and Montreal to the west.

St. Lawrence Lowlands
St. Lawrence Lowlands region

The St. Lawrence Lowlands is a region in Canada which are northeast of the Shield and south of the Appalachian Region. It is broken down into three parts:

West St. Lawrence Lowland

The West St Lawrence Lowland is a limestone plain between the Shield and Lakes Huron, Erie, and Ontario. A broad, shale lowland separates it from a broader dolomite and limestone plateau west of Lake Ontario. The plateau here is bordered east and west by the Niagara Escarpment, which has created gently sloping southwest hills. Glaciation has left an uneven layer of glacial till on this southern tip of Ontario, which contains different types of particles that accumulated from retreating glaciers in the past.

The glacier paused in the retreat at the southern edge of Lake Ontario between 14,500 and 12,500 years ago. A glacial lake left level clay and sand plains near the present lakes.

Central St. Lawrence Lowland

The West St Lawrence Lowland is located in the middle of Canada. It is a limestone plain surrounded by shale lowlands on the west and a broader dolomite and limestone plateau on the east. From the escarpment, the landscape slopes gently to lakes Huron and Erie with an elevation of 173 meters. As a result of glaciation, this location has extensive rolling drumlin fields where land is inlaid with a mixture of clay, sand, and other additives.

The western plateau saw a brief pause in glaciers 14-12,500 years ago. The clay and sand plains around today’s lakes were from glaciers’ prior history of glacial lakes that had to melt.

Central St. Lawrence Lowland

Geologically, this subregion is undulating, with some sedimentary rock hidden by glacial and marine deposits. The seven Monteregian hills are aligned west to east and exuded volcanoes made during the Atlantic Ocean’s making 120 million years ago.

The low, rolling moraine trends southwest from near Québec City to near the Vermont border. Near Québec City, shallow elevation terraces were deposited in the Champlain Sea, flooding the newly deglaciated lowland and leaving behind high, sandy terraces for streams to erode along with polder systems.

East St. Lawrence Lowland

This area is located at the St. Lawrence estuary and stretches into the Gulf of Saint Lawrence. It then narrows northeast at Belle Isle Strait. There are smaller, less mountainous regions in the north region of the Gulf of St Lawrence, such as Îles de Mingan; there is also a less mountainous coastal plain at less than 100 m in northwestern Newfoundland. There is also a more prominent, undulating plateau at 100–200 m with a central spine at 300 m on Île d’Anticosti. These fragments have a smooth terrain. The surface can be influenced by flat or gently dipping sedimentary bedrock, and various surface conditions may exist depending on the surface slope, amongst other factors.

Google maps of the St. Lawrence Lowland

St. Lawrence Lowland is a plateau along the St. Lawrence River between Québec City in the east and Brockville, Ontario, in the west, including the Ottawa River valley from St. Lawrence east to Renfrew, Ontario. The total area of this plain is 46,000 km2, with 5,000 km2 being in the U.S.

The St. Lawrence River and Great Lakes have been essential transportation routes for thousands of years because the region of Ontario is ideal for industrial, tourist, and agricultural activities.