Yesterday Jonah Goldberg pointed to a story about previously unknown volcanoes 13,000 feet beneath the Arctic Ocean and asked:
“am I crazy for wondering why this story doesn’t even address — if only to shoot down — the idea that maybe it’s volcanoes, and not global warming, that are causing the melting ice caps?”
Goldberg isn’t crazy, nor is he the only one wondering such a thing. In December 2007 Ralph von Frese, an earth sciences professor at The Ohio State University, reported newly discovered volcanic activity beneath the ice sheet that covers nearby Greenland. His analysis determined that it is possible that recent volcanic activity there might melt enough water at the bottom of the ice sheets to accelerate their flow. Von Frese concluded that:
The behavior of the great ice sheets is an important barometer of global climate change . . . However, to effectively separate and quantify human impacts on climate change, we must understand the natural impacts, too.
That seems like a rather pragmatic approach, so let’s attempt to quantify the impact of the volcanoes recently discovered at the top of the world. What the Woods Hole Oceanographic Institute’s researchers found was a series of explosive volcanoes along the Gakkel Ridge, an underwater mountain chain 1,100 miles long. There, a series of earthquakes in 1999 were the result of volcanic eruptions each “as big as the one that buried Pompeii.”
Geologists tell us that when Mount Vesuvius erupted in 79 AD, burying the ancient Neapolitan city, it launched a cubic mile of molten rock into the atmosphere. Doing a little bit of math (see below) we find that a single Pompeii-sized eruption would release enough subterranean heat into the Arctic Ocean to put a hole in the polar ice cap the size of Massachusetts.
Granted, the expanse of the polar ice cap is much greater than the size of the Bay State, but the story says that there was apparently more than one eruption in 1999 when seismologists first learned of the issue. Climatologists before had barely even considered the effect of undersea volcanoes, whose effects are obviously not insignificant. The magnitude of the recently discovered eruptions undoubtedly explains some proportion of the melting ice caps that many before have attributed to the effects of man. As von Frese said, this little understood natural phenomenon deserves more scrutiny.
I say all this to point out what should be obvious but apparently isn’t: we barely understand the world around us. In all of recorded history we have only begun to scratch the vast amount of knowledge of the workings of our magnificent planet. This world is so enormous that we apparently have even missed the existence of one of Earth’s most powerful forces—a volcanic explosion—directly beneath this supposedly well studied area. For man, who possesses so little knowledge, to conclude that he and he alone is responsible for the changes we now observe around us is the height of hubris. Volcanoes, it turns out, rise to even higher heights than hubris.
That “little bit of math” part follows after the jump.
Before the math, I probably need to explain a little bit about enthalpy. A “little bit” is all I know, since it has been probably two decades since I’ve even said the word “enthalpy.” Still, the concept is pretty simple. If it takes a certain amount of heat energy to raise the temperature of a given quantity of something by one degree, it takes ten times that heat energy to raise the temperature of that same quantity by ten degrees. That simple linear equation holds until you reach the point at which its phase changes. For example, to raise the temperature of one kilogram of water one degree Celsius you must add 4,186 joules of heat. That means that to go from 0 degrees to 100 (from the freezing point to the boiling point) requires the addition of 100 times that amount, or 418,600 joules. However, that’s just the energy required to bring it to the boiling point. To actually boil the water takes another 2.3 million joules. That’s why when you heat water on the stove, it warms up quickly, but it always seems to take forever for it to actually boil.
The same works in reverse. When H2O goes down a phase it gives off the same amount of energy that it took to change into that phase. It’s not just water that behaves that way; every substance does. Even rock.
A cubic mile of molten rock, like was launched by Vesuvius on to Pompeii, converts to 4.186 billion cubic meters. At a density of 3,000 kilograms per cubic meter, that much molten rock works out to be approximately 1.25 x 1013 kg.
Basaltic magma has a specific heat of 1,000 joules per kilogram per degree Celsius. In other words, a kilogram of magma releases 1,000 joules of heat energy for every degree it cools until it transforms into a solid. A kilogram of molten rock at 1350 degrees Celsius, therefore gives off 250,000 joules of heat as it cools to its crystallization temperature of 1100 degrees Celsius. Passing through that phase from liquid to solid, that kilogram releases another 400,000 joules of heat. Then as the solid rock cools from 1100 degrees to 0 degrees Celsius it releases another 1,400 joules per degree, or 1,540,000 joules. In total, one kilogram of molten basalt at a temperature of 1,350 degrees releases 2,19 million joules of heat into the surrounding atmosphere. Multiplying the weight of a cubic mile of lava by the heat energy released per kilogram and we find that a Pompeii-sized underwater eruption releases 2.739 x 1019 joules of heat into the sea.
One kilogram of ice at 0 degrees Celsius requires the addition of 333,550 joules of heat energy to turn it into a liquid. Dividing that number into the quantity of joules of heat released by the volcano that we calculated above, we find that the cubic mile of magma can melt roughly 82 trillion kilograms of ice. A cubic meter of ice at 0 degrees weighs 917 kilograms, so that works out to roughly 90 billion cubic meters of ice melted by our undersea volcano.
Because of the shifting currents beneath the North Pole, the sea ice there is only two to three meters thick. Dividing 3 meters into the volume of ice that our volcano melted, we find that it would cover an area of just under 30 billion meters square, or a little less than 30 thousand square kilometers. Convert that into English, and it works out to 11,532 square miles of ice three meters thick, or an area about 10% larger than the state of Massachusetts.
Obviously, I’ve made some simplifications, like ignoring whatever effects the pressure of 13,000 feet of sea might have on the equation, and I haven’t taken into account the change in melting point as a result of the salinity of the ocean. But this is probably close enough to demonstrate that Jonah Goldberg’s original question is worthy of much more analysis.
In short: how much polar ice is melted by an undersea volcano? A whole lot.