How To Get Clean with a Batholith
During this past summer there was some worry about Mt. Dutton, near King Cove. Earthquakes in the area warned that magma, the melted rock and trapped gases from deep in the earth, might be moving under the region. Since Mt. Dutton is a volcano, there was a chance of magma moving under and up through the mountain in a volcanic eruption. Because of that possible danger, Mt. Dutton was quickly furnished with seismographs to telemeter the tremors to the Alaska Volcano Observatory and watching scientists.
The earthquake activity died away, and to everyone's relief, no eruption has occurred--yet, at least. But that doesn't mean nothing happened.
If magma is shifting and stirring but does not reach the surface, all of it won't necessarily drain back down to its deep sources. Nor is it necessarily biding time until a future eruption. The magma may stop and solidify in its tracks.
Should that happen, the residents of King Cove may encounter an igneous intrusion instead of an eruption. They may even find themselves sitting atop a batholith.
Igneous rocks are those that were once liquid-hot. If they burst through the surface of the earth before they solidify, they're volcanic. If they solidify underground, they're plutonic (after the mythic god of the underworld, not the Disney dog). Smallish intrusions of plutonic rock come in dikes and sills; really big ones--whole magma chambers solidified underground--are called batholiths, from Greek words for deep and rock. The visible portion of Mt. McKinley is a batholith, and far from the largest known. A fair catch-all term for all sizes of intrusion formed under the earth's surface is pluton.
Igneous rocks come in many varieties, with differences caused by the chemical composition of the parent magma, how much of the basement rock melted into the magma, and how rapidly the molten mass cooled into a solid.
Granite, the stone of which Mt. McKinley is made, is a plutonic rock formed from a magma chemically identical to that producing volcanic obsidian, the greenish-black glass that makes razor-sharp arrowheads. The rough, grainy granite took a long time to cool underground, so it contains many coarse crystals, while the glassy obsidian solidified so quickly out in the air that no crystals could form in the mix.
If the subterranean stirrings at King Cove lead to a new pluton, it might give the town a new energy source. Admittedly, the chances for such a beneficial outcome are exceedingly small. For one thing, the magma will have to stop fairly near the surface. For another, it would have to form a good-sized intrusion. But if those things happen, and if the local water table cooperates, the cooling magma might give rise to new hot springs. By pumping water down to the hot rock, it might even be possible to create a kind of artificial hot spring, or at least a geothermal well.
Some scientists believe that it is a batholith of just this sort that provides the heat for Pilgrim Hot Springs near Nome. Since those springs have been providing hot water for at least hundreds of years, the people of King Cove need not worry that their batholith would cool off very soon. However, they might have to wait a few generations for it to provide hot water instead of steam in their pipes.
