The Hudson Bay Lowlands (HBL) is the rocky interior lowland region encircling Hudson Bay. This vast area is characterized by an immense wetland system and a landscape still recovering from the last ice age. It is a massive, flat plain that acts as a transition zone between the boreal forest to the south and the Arctic tundra to the north.
Defining the Hudson Bay Lowlands
The Hudson Bay Lowlands is the largest wetland complex in Canada and one of the largest in the world, covering approximately 320,000 square kilometers. This expansive region is situated between the southern and western shores of Hudson and James Bays and the inland edge of the Canadian Shield. The Lowlands span across three provinces, with the majority lying in northern Ontario, and smaller portions extending into Manitoba and Quebec.
The Lowlands are characterized by extremely low relief, with local elevations typically under two meters and maximum elevations reaching only about 120 meters at the inland boundary. Numerous wide, slow-moving rivers, such as the Severn, Winisk, and Attawapiskat, drain through this plain, carrying fresh water into the saltwater of Hudson and James Bays. This low-lying, poorly drained environment creates a landscape of bogs, fens, and swamps.
Geological Foundation and Isostatic Rebound
The region is an extensive sedimentary basin where flat layers of Paleozoic and Mesozoic sedimentary rock, primarily carbonate strata like limestone, rest atop the much older Precambrian Canadian Shield. This sedimentary overlay distinguishes the Lowlands from the rugged, exposed granite and gneiss bedrock of the adjacent Shield. The lowland nature is a direct result of the immense weight of the Laurentide Ice Sheet, which was centered over this region during the Pleistocene Epoch.
The ice sheet compressed the Earth’s crust, causing the land to sink. When the ice melted about 8,000 years ago, the depressed area was initially flooded by the Tyrrell Sea. Since the removal of the weight, the land has been slowly rising in a process called isostatic rebound. This geological uplift is one of the continent’s most rapid, occurring at a rate of up to 1.3 meters per century in some areas.
This ongoing rebound causes the ancient seafloor to emerge, resulting in conspicuous geological features known as raised beaches. These hundreds of low, dry, gravel ridges, which were once shorelines, form the “rocky” component of the otherwise ill-drained plain. The uplift continues to expose new land, causing the Hudson Bay shoreline to retreat northward by several meters each year.
Ecology of the Muskeg and Permafrost Landscape
The environment is dominated by muskeg and permafrost. Muskeg, a type of acidic peatland, covers the majority of the Lowlands, making it the world’s second-largest peatland complex. Poor drainage is exacerbated by underlying impermeable silt-clay soils and the presence of frozen ground.
Permafrost, ground that remains frozen for at least two years, is present throughout the region. The Lowlands sit in a zone of discontinuous permafrost, often found beneath insulating layers of peat. This frozen layer acts as a barrier, preventing water from draining downward and forcing it to pool on the surface. This saturated condition fosters the growth of sphagnum moss and other water-tolerant vegetation, which slowly accumulates to form deep peat deposits.
The landscape features formations like peat plateaus and palsa fens, which are mounds of peat elevated by an ice core within the permafrost. The Lowlands support a mix of black spruce, tamarack, sedges, and arctic shrubs. This environment provides habitat for specialized wildlife, including polar bears along the coast and vast numbers of migratory waterfowl and shorebirds.