Amazing. I don't know of anything in human experience that would have led someone to anticipate this -- perhaps one of our geo-knowledgeable people can say more about this.

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On a tangent --

Mother Nature can store up some remarkably nasty stuff underground:

...Vast volumes of basaltic lava paved over a large expanse of primeval Siberia in a flood basalt event. Today the area covered is about 2 million km² and estimates of the original coverage are as high as 7 million km². The original volume of lava is estimated to range from 1 to 4 million km³.

http://en.wikipedia.org/wiki/Siberian_Traps

Of course that was about 500 million years ago. In what is almost the modern era, from the perspective of deep geology, events of this sort have been more moderate:

...The bulk of the volcanic eruption occurred at the Western Ghats (near Mumbai)some 66 million years ago....it is estimated that the original area covered by the lava flows was as large as 1.5 million km². The present volume of lava is estimated to have been 512,000 km³.

http://en.wikipedia.org/wiki/Deccan_Traps

And almost yesterday:

The Yellowstone Caldera, sometimes known as the Yellowstone supervolcano, is a volcanically active region in Yellowstone National Park. It measures 55 kilometers (34 mi) by 72 kilometers (44 mi)....within the past two million years, it has undergone three extremely large explosive eruptions, up to 2,500 times the size of the 1980 Mount St. Helens eruption....the most recent such eruption produced the Lava Creek Tuff 640,000 years ago and spread a layer of volcanic ash over most of the North American continent. Smaller steam explosions occur every 20,000 years or so; an explosion 13,000 years ago left a 5 kilometer diameter crater....

http://en.wikipedia.org/wiki/Yellowstone_Caldera

The widespread image of nature as benign and stable is false, and is a psychological obstacle to proper appreciation of the growing climate crisis.

Words and ideas I offer here may be used freely and without attribution.