An exploratory geothermal drilling operation in Hawaii has pierced a large, shallow and unexpected active magma chamber. Wait, this is more interesting news than it may seem at first blush.

The top of the chamber is around 2.5 km below the surface of Kilauea lava fields on the big island of Hawaii. That is very shallow... only a little over a mile - about 12 Manhattan city blocks - which isn't much in terms of crust thickness. But what makes this a particularly interesting find is that the molten rock down there isn't just some random lava flow, it's a giant cauldron of churning, incandescent liquid... a cavernous magmatic vault in the crust... and it's changing.

To give context, continents and ocean floors are made of very different kinds of rock, with major difference between them. The ocean floor includes the vast abyssal plains, deep-ocean trenches, and volcanic submerged mountain chains along the mid-ocean ridges. Most of that is made of some pretty basic planetary material: basalt, which sweats and oozes from raw upper-mantle rock when it reaches melting temperature. If you dissolve a little water into mantle rock - even as little as one or two percent water permeating the minerals - the melting temperature drops by hundreds of degrees. Under a world-sized ocean of water, the hottest mantle rock - freshly convected up from deeper places - can partially melt. When that happens, pools of buoyant magma distill from the denser solid rock into huge, deep chambers of roiling white-hot liquid. Magma close to the surface can erupt as lava, but deep chambers can sit for ages without erupting... slowly cooling and crystallizing into interesting things like granite, which makes up the continents.

Magma chambers are where, ultimately, the continents of our planet come from. Without a liquid ocean to wet and melt the upper mantle, volcanism would occur rarely... only where massive enough reservoirs of heat can build up very close to the surface, where lower pressures allow hot rock to liquidate. That's what happens on Venus. Every few tens of millions of years, enough throbbing heat builds up under the solid, dead crust to catastrophically melt whole regions of the surface at once. When that happens titanic volumes of the crust simply dissolve, releasing whole sea-volumes of lava to flood the world in glowing torrents that would be visible from space.

Luckily, Earth doesn't have that problem. Our oceans allow for magma to form at much lower heat densities, making magma chambers smaller, more common and more manageable... which allows life to persist over geologic time. Because magma chambers can form gradually, they can also cool gradually, and that slow cooling leads to the kinds of rock that you need to make big, tall, persistent continents. Granite is lighter than basalt and floats higher on the mantle, allowing for landmasses above sea level that stick around for eons and support a stable land-based ecology.

Which brings me back to why this discovery is so interesting. When the chamber was discovered it was found to contain liquid dacite, which is halfway between basalt and granite in composition... well on the way to forming continent-style rocks. This chamber is likely to be only about half a century old, based on where it is below lava flows of known age. This is interesting because we now have a window - in real time - into physical processes that are otherwise very difficult to witness in action.

For most of scientific history geologists have had to infer what kinds of processes operate in magma chambers, because it hasn't been practical to watch such processes happen in real time and in nature. We actually understand a lot about magma chambers, using information from experiments in the lab coupled with field work, despite never having a front row seat to the actual mechanism kilometers below the Earth's surface. Like evolution, the process that forms continents is difficult to catch in the act on the time scale of a human lifetime. Mostly we see the results of those processes after the fact, and have to piece together the entire scenario bit by bit using exploration, logic, evidence, and intellectual honesty as our tools.

Now we have a new window into the planet, and igneous geologists are thrilled, as they should be, showing once again the difference between science and faith. If the deep structure of the Earth was an article of faith in the world's major religions, discoveries like this new magma chamber would be lightning rods of controversy. Did those scientists really find that magma down there? Or are these simply more lies from the Magma-ists? How can magma be possible, when the Bible clearly states that "fountains of the deep" brought forth the Flood? Obviously one cannot have both magma and liquid water in the mantle, but the inerrant dogma must be true... therefore magma chambers cannot exist, and continents cannot move. How can we allow the indoctrination of our children into the atheist doctrine of Anti-Floodism? Shouldn't both sides be taught in science classes, to preserve the sanctity of academic freedom?

No.

Science accepts new ideas, rejoices when new discoveries are made that overturn or clarify earlier models, and moves on. If something new is discovered about how magmas crystallize, something novel and surprising, you can rest assured that many new papers will be written and many new careers will be made. If the old guys are wrong, some of them might grumble but most will applaud. That's how science works. Faith alone would still have us throwing human sacrifices into volcanoes, instead of using them to power our cities.

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Tags: Hawaii, Kilauea, geology, magma

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Comment by Planetologist on December 18, 2008 at 5:40pm
Indeed, it is truly laughable how wildly the YECs will twist and fold reality - including snipping off the bits that annoy them - to prop up their Paleolithic fireside tales.

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