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.


Rod said...

Please forgive the completely off-topic comment!

WoGE#167 has been languishing for so long on Ron Schott's site that the Google imagery has actually changed. I think it's probably just escaped the attention of the geoblogosphere because the momentum was lost back in early spring, but it's time to get things rolling again. Ron tried to give a big hint recently, but he did it through Twitter. I thought I'd take the more drastic measure of posting a hint on some previous WoGE winners' sites: Windley and Allen, 1993.

Raymond said...

I am an Inuk formerly from Arviat in Nunavut Canada on western Hudson Bay, some years ago I saw a computerized generated image on how the Hudson Bay will look like in 5,000 years from now, it looked like a very narrow lake, are there websites that one can see this? thanks.

Chris M said...

Raymond, I haven't seen a map like that, but it sounds very interesting!

john delano said...

This is an area Hudson Bay that has a very low "gravity" reading because of very dense rock deep down , just like an ocean trench.
The rest of the gravity low reading is the massive magma below the deep layer down to 30,000 feet-6 miles down!
It is impossible for a 50,000 year ago ice sheet the size of 2 miles high to create a magma mass.
The heat of friction under an ice flow at least 6 miles deep into the crust and 10 miles high to develop the magma mass described.
That size ice mass had to have a date that should be dated in the surrounding rock o 600 to 400 million years ago.

john Delano