 Most diatremes in the Northwest Territories were formed by volcanic eruptions between 45 and 75 million years ago during the Eocene and Late Cretaceous periods.More recent volcanic activity has created a northwest trending line of volcanic rocks called the Wrangell Volcanic Belt.This volcanic belt lies largely in the U.S. state of Alaska, but extends across the Alaska-Yukon border into southwestern Yukon where it contains scattered remnants of subaerial lavas and pyroclastic rocks which are preserved along the entire eastern fringe of the ice covered Saint Elias Mountains.