Posted by Chris M Saturday, June 13, 2009

Isostatic Rebound Hudson Bay

The subject of this month's Accretionary Wedge is "Let's do a time warp". Basically, what past (or future) geologic events would you like to be able to observe.

The geologic event I choose is the isostatic rebound of the Hudson Bay region. At the end of the Pleistocene and the beginning the Holocene, the massive ice sheets covering northern North America began to melt. As the weight of thousands of meters of ice over the Hudson Bay region was removed, the surface began to rise.

As the land continued to rise, new shorelines were repeatedly being formed, as the old shorelines were elevated higher. In some places, over 175 old shorelines ring the present bay level. This is equated to over 300 m over rebound in places. And it is still rising.

If I was in a space ship, watching this event unfold in a few minutes rather than thousands of year, I would see a huge mass of ice melting, followed by a quick jump of the land surface. As time would pass, the speed of the rise would slow down. On the surrounding land surface, almost bare rock surfaces, sweep clean of soil by the glaciers, would slowly become colonized by mosses and lichen. Soil would slowly begin to form, allowing shrubs and trees to gain a foot-hold. Water that would have originally laid on the nearly flat surface, would have started to cut the beginnings of stream channels.

I have reached the present. What does the future hold? The land will continue to rise, in some places still over 100 m. As the climate warms (at least in the relative future), more trees will move even more, as the rate of soil creation increases with the warmer temperatures. Lakes will fill in and drainages patterns will become less deranged.