woensdag 10 juli 2013

Melting of the ice, backwards

A few days ago, two workmen were fixing my sewer and plumbing system underneath my house (It was kinda smelly). During the coffee break (which is the theme in my blog, all good things come from a coffee break), I had to explain what I did at the university. So I explained that I was looking at the motion of the Earth's crust due to ice loading during the late-Pleistocene ice age (well not in those words, and I did not mention, that I was doing this with satellite data, because my experience tells me to leave this part out. If you use the word satellites, people just stop listening and laugh). They found it very interesting ;).

I know, it is an abstract subject and difficult to grasp (it took me several months to fully understand the complexity of the problem, I am still working on how to solve it). Last week I needed to look at the ice sheet, that caused the motion of the crust that we observe today. People have made models on the growing and melting of this ice sheet, using all kinds of observations, from markings on rocks, bird droppings and pre-historic campfires. One of these models is called ICE-5G, constructed by W.R. Peltier from the Department of Physics in the University of Toronto, Canada.

To get a feeling that an ice sheet can deflect the Earth's crust, you should first get a sense of magnitude of this ice sheet. Therefore I made an animation that shows the growing of the ice sheet until its largest magnitude 21,000 years ago (21 ka). The animation starts with the present and goes back in time with steps of 500 years. The color scale illustrates the thickness of the ice sheet, going up to 3 km (that is a lot of ice).


I have not plotted topographic height variations, because I want to emphasize the ice sheet thickness (oh, and really watch the movie at 720p HD).

The movie starts with the view of Northern Europe. The current ice sheet of Greenland is visible and a little bit of ice on the Russian island, called Nova Zemlya (a very important island in Dutch history). The first 8500 years back in time does not show any ice in North Europe. So it gives you some time to orientate yourself. The viewpoint rotates around Scandinavia from Canada and ends in Russia. you see Scandinavia in the middle. 

When going further back in time, some ice is visible in Sweden. Also the ice on the island Spitzbergen grows a little bit. This growing (or melting, because we go back in time, get it?!?) continues and even ice in Scotland is accumulating. The Last-Scottish ice sheet peaks at 13,000 years ago, but vanishes again, when we continue to go back in time. The ice on North Europe, Iceland, Spitzbergen and in the Barentz Sea, however, keeps on growing. 

The Scottish ice sheet reappears 15,500 years ago (or melts away, keep focused, its so confusing.) and continues to grow. Eventually it will be connected to the big ice sheet on top of Scandinavia. This ice bridge is resting on the continental plate underneath the North Sea. Oh yeah, there is a large spike at 18,000 years, but I think this is a glitch in the model/processing (I don't believe in extreme local snowfall), ignore it. 

21,000 years ago the North Europe ice sheet is at its largest. In all its glory pressing down on dirt, rock and crust. This impression, this footprint is still observed today as very small land uplift rates and gravity field changes.


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