Cordilleran Ice Sheet - Sea Levels During Glaciation

Sea Levels During Glaciation

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, 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. This was because the much greater thickness of the centre of the ice sheet served to push upwards areas at the edge of the continental shelf in a glacial forebulge. The effect of this during deglaciation was that sea levels on the edge of the ice sheet, which naturally deglaciated first, initially rose due to an increase in the volume of water, but later fell due to rebound after deglaciation. Some underwater features along the Pacific Northwest were exposed because of the lower sea levels, including Bowie Seamount west of the Queen Charlotte Islands which has been interpreted as an active volcanic island throughout the last ice age.

These effects are important because they have been used to explain how migrants to North America from Beringia were able to travel southward during the deglaciation process due purely to the exposure of submerged land between the mainland and numerous continental islands. They are also important for understanding the direction evolution has taken since the ice retreated.

Even today, the region is notable for its rapid changes in sea level, which, however, have little effect on most of the coast due to the numerous fjords.