Sharon Begley of The Wall Street Journal is one of the finest science reporters around. Her Friday column was typically interesting. It's about how global warming might lead to increased tectonic and volcanic activity:
One cubic meter of ice weighs just over a ton, and glaciers can be hundreds of meters thick. When they melt and the water runs off, it is literally a weight off Earth's crust. The crust and mantle therefore bounce back, immediately as well as over thousands of years. That "isostatic rebound," according to studies of prehistoric and recent earthquakes and volcanoes, can make the planet's seismic plates slip catastrophically, and cause magma chambers that feed volcanoes to act like bottles of shaken seltzer. "It's unavoidable that glacial retreat will induce tectonic activity," says geoscientist Allen Glazner of the University of North Carolina, Chapel Hill.
Obviously, these predictions are pretty hypothetical. But I'm not sure I want to live in a world where Sweden, Iceland and Northern Canada are full of Krakatoas...
[Thanks to the astute comments of Markk, I though I should make it clear that not all areas of the globe are equally affected by glacial retreat. Geologic studies have only shown that volcanoes in Iceland, the Mediterranean, Antarctica, Northern Europe, Northern Canada and eastern California were awakened by the disappearing glaciers.]
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Right - just like all the volcanos we see in the US midwest about 10000 years ago when even bigger glaciers retreated. Wait I can't find any. I am worried about warming, but not because of this.
Thanks for your comment, and sorry if my original post wasn't clear. This increased tectonic activity doesn't apply to all areas of the world. But when ice sheets retreated 10,000 years ago, Iceland experienced a surge in volcanic eruptions. Volcanoes in the Mediterranean, Antarctica and eastern California also seem to have been awakened by retreating ice.
What a notion!
Let me see if I understand this: there's a guy standing next to a mountain of ice. The ice, weighing in at a ton per cubic meter, is a big, big load on the earth below.
If the guy stands there, in place for 10,000 years with a shield that deflects falling ice while wearing a raincoat and sturdy waterproof boots -- eventually the ice will disappear, the neighboring earth with bounce back, throwing the pedestrian sideways, and pushing the edges of the tectonic plate down,down toward the mantle...
Now here's the part i don't quite understand.
As the earth rebounds, part of the plate goes up, the edge of the plate goes down..and then something happens down there in the darkness that squeezes rocks into a molton state, squishing them until they can't stand it and then boom! Boom! Boom! There are guysers of lava shooting up through volcanoes? And then our poor pedestrian, who hasn't had time to take off his boots, gets buried in lava and ash?
Is that what you're saying..or what Professor Glazner is saying?
What's missing from this tale is the part I can't see.
The Under-the-Ground part. Have I got it right?
Isostatic recovery is visible in archeological sites in Scandinavia, where the major Viking settlements of 1,000 to 1,500 years ago, seaports, are now very roughly 30 feet above sea level now. (This is going back to my visits there as a young student forty years ago so the numbers are very approximate). They even found that the piers of the docks were gradually extended down the bay as the water retreated over the centuries.
Second point, isostatic recovery won't cause volcanoes to form, but as I understand this post might add enough stress to existing volcano magma chambers (sources of lava under the volcano) to eventually cause eruptions. Since the isostatic recovery occurs over centuries, we're not talking about someone getting knocked over when the ice melts.
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