evilgenius wrote:I've often wondered what these changes mean for the part of all this we can't see from above, the flow of molten or semi-molten rock underneath. Take Greenland, for instance, it's covered in ice. Isostasy means that it will remain at equilibrium as the ice covering it goes away. That also means it won't project as deeply into what lies below it. What's that going to mean for the flow of rock? I wonder if anybody is doing any studies about earthquake occurrence and Arctic melting, whether there is any correlation far enough out in the timeline from observed changes according to how fast rock moves? Same goes for if the hotspot under Iceland could be affected? You'd think not, but pressure differences have a way of changing complex systems in ways that are unexpected. Anyway, just a thought.
Yeah, Plantagenet, this warming trend during winter may be bad news for the Greenland ice cover, and that chain of land north of the Northwest Passage. It will be years yet before they melt out enough to cause the huge sea level rise most people fear, but along the way because they cover a huge surface area they will melt out enough to endanger places like the Nile Delta. We don't know if they are going to do that in a hurry, but if this trend keeps up you can say with remarkable certainty that they will in time. People argue that places like Greenland both lose and gain ice cover. What that means, though, is that for some period of the year there will be more water in the ocean, especially as the process goes through a tipping point. Even if some kind of remarkable feed back cycle we haven't thought about occurs and puts a stop to this I don't think at this point that the most vulnerable low lying areas can escape. It's so scary because the refugee crisis we have now is too much for us, and it is nothing like the one that changes like that would bring.
Basically, you can look upon events like Hurricane Katrina as one offs, or you can look at them as warnings of what is to come, telling you to make this or that stronger, or abandon one concept or another. Or you can refuse to change anything, not learn from the opportunity, and be totally unprepared for when anything similar, or worse, happens down the road. Katrina (and Sandy) was a trial run for how cities can be affected by sea level rise. It isn't just the emotional toll we should concentrate on. How effective were the countermeasures? Can we build sea walls and dykes that will work? If we can it would be easier to build them now, while we can still access the ground with relative ease. We have to consider what happens to them during storms. How does that change the calculus for whether people shouldn't simply move from low lying areas? What's the real time frame for moving people if the world does have to make those tough choices?
Because the chunk of plate the Greenland land mass sits on has a certain amount of flexibility it works kind of like a paper plate. If you stretch a sheet over the open top of a large box or similar object and set a paper plate on the taut sheet it is analogous to the continental plate floating on the magma below. If you pile ice cubes on the middle of the plate what happens? The center of the plate goes down just like you wrote, but the out edge of the plate also goes up a little bit. If you let the ice melt and run away the center of the plate will indeed rise back closer to its former altitude, but at the same time the outer edge of the island, much of which is mountainous, will also sink back down as the plate is not as heavily depressed in the center.
This kind of plate flexing is already a well known phenomenon, the Laurentide ice Sheet depressed everything in Eastern Canada and the Midwestern and eastern USA as far south as 39 degrees latitude in its extreme extent. as a result the state of Michigan and the province of Ontario are still rebounding in altitude even today, 17,000 years after the ice cap melted away. At the same time the coastal land in Virginia, Maryland and North Carolina is sinking as the shape of the continental plate returns to its pre ice cap shape.