 Farther north it is less clearly defined, forming a large arch that swings westward through central Yukon.Volcanoes within the British Columbia portion of the Northern Cordilleran Volcanic Province are disposed along short, northerly trending en-echelon segments which, in the British Columbia portion of the volcanic province, are unmistakably involved with north-trending rift structures including synvolcanic grabens and half-grabens similar to the East African Rift, which extends from the Afar Triple Junction southward across eastern Africa.The Northern Cordilleran rift system formed as a result of the North American continent being stretched by extensional forces as the Pacific Plate slides northward along the Queen Charlotte Fault to the west, on its way to the Aleutian Trench, which extends along the southern coastline of Alaska and the adjacent waters of northeastern Siberia off the coast of Kamchatka Peninsula.