The Queen Charlotte Islands were covered in glaciers during the LGM .
Because of the weight of the ice , the mainland of northwest North America was so depressed that sea levels at the Last Glacial Maximum were over a hundred metres higher than they are today ( measured by the level of bedrock ) .However , on the western edge at the Queen Charlotte Islands ( which , contrary to popular myths of ice-free refugia , were entirely glaciated during the LGM ) the lower thickness of the ice sheet meant that sea levels were as much as 170 metres lower than they are today , forming a large lake in the deepest parts of the strait .