How does plate tectonics explain the distribution of Canada's major mountain belts?

• A. The Appalachian Mountains formed by ancient collisions; the Cordillera is an eroded structure.
• B. The Western Cordillera formed by subduction and uplift along the western margin; the Appalachians formed by ancient collisions; interior plains are eroded remnants.
• C. All mountains formed by meteor impacts.
• D. The mountains are only due to glacial carving.

Answer: (B)

Plate tectonics shows how different interactions at a continent’s margins create distinct mountain belts and landforms. Along the western edge, subduction of oceanic crust beneath North America lifts and deforms the crust, building the Western Cordillera with tall, rugged mountains and ongoing tectonic activity. Out on the eastern side, ancient continental collisions welded landmasses together long ago, forming the Appalachians; over hundreds of millions of years, erosion has worn them down to lower, rounded remnants. The interior plains lie inland of these belts and are largely flat because the old mountains have been worn away and sediments have accumulated, creating broad plains. So, subduction and uplift explain the western cordillera, ancient collisions explain the Appalachians, and erosion accounts for the eroded remnants that make up the interior plains.