The Socorro Magma Body

Sandhill cranes only dance during the winter at New Mexico’s wildlife refuges.

Volcanologists and other Earth scientists do their thing year-round at one particular reserve:  the Sevilleta National Wildlife Refuge, located a few miles north of the city of Socorro, New Mexico.  It’s sits some 70 miles south of Albuquerque and about 50 miles east of the National Radio Astronomy Observatory’s Very Large Array.

The boffins aren’t installing seismometers at Sevilleta to monitor birds.  They are trying to learn more about the second-largest collection of magma ever found in Earth’s continental crust.  This underground magma sits just 12 miles  below the nature reserve and other nearby areas.

The Socorro magma body

It isn’t a volcano, since it hasn’t erupted yet. Technically speaking, the Socorro magma body is a sill (Fialco and Simons). That’s what geologists call magma that flows into other rock formations underground.

The Palisades, near New York City, is probably the most famous example of a sill.

640px-Edinburgh_Salisbury_Crags_2004-05-18

Salisbury Crags, near Edinburgh, Scotland, is another example of a sill. Image by an unattributed author.

Like all sills, the Socorro magma body covers a lot of area (a couple thousand square miles), but it’s shallowless than 500 feet thick. (Chapin and others)

But, unlike the Palisades, this New Mexican collection of magma is still on the move. Geologists know this because the region has frequent earthquake swarms and the ground there is rising slowly. (Chapin and others)

Will the molten rock eventually erupt, or will it stop moving and slowly cool back down into solid rock, like the Palisades did?

No one knows, so scientists are watching the Socorro magma body closely and trying to learn everything they can about it.

Why is there magma down there?

You don’t have to be a scientist to realize that some major geological violence has happened in this part of the Southwest.

This is especially noticeable in and around Albuquerque, New Mexico.

Although the city seems to sit on flat ground, it’s really in a valley that slopes down very gently to the Rio Grande. The sharp cliffs of the Sandia Mountains border this valley to the east, and Seven-Mile Hill, topped by a row of old volcanoes, marks the western edge.

640px-ABQ-West-Mesa

This is what Albuquerque looks like from the west mesa volcanoes.  Image by Wxstorm.

Some ancient geological movements dropped the valley floor many hundreds of feet straight down.

Albuquerque sits in what is known as the Rio Grande Rift, a system of lowlands named for the river that flows through it today. This rift formed in response to complex regional geologic and plate tectonics situations. Experts are still trying to work out the details. (Chapin and others; Zandt)

Another response to those geological forces was intense volcanism.

The view from Sandia Peak some 30 million years ago would have shown lava fountains west of the valley, not cinder cones.

And at least 19 of Earth’s 47 largest known eruptions—all of them VEI 8 or higher—happened in the New Mexico/Texas/Colorado region back then. (Mason and others) That period, which lasted tens of millions of years, is sometimes called the ignimbrite flare-up.

The geological situation that was causing it changed before the continent could split completely apart along the Rio Grande Rift. Basically, some 20 million years ago the San Andreas, which had been a subduction zone, turned into the fault line that we know today. (Chapin and others; Zandt)

This brought the flare-up to an end, but some volcanism has continued in the region ever since. Earth’s crust has been thinned by those ancient events, and the deeper layer underneath the crust has been disrupted. Magma can still leak through to the surface in some places.

Today experts say there is a 1% chance of an eruption in New Mexico during the next 100 years. Areas most at risk are in northern New Mexico and along the Rio Grande rift, where attention is focused on the Socorro magma body.

How much risk is there from the Socorro magma body? Scientists can’t be sure. It depends on whether that magma is the runny type that flows smoothly, like lava at a Hawaiian volcano, or whether it’s the sticky kind that clogs up volcanic conduits so that the volcano pressurizes and then explodes.

Both types have been frequently erupted in this region.

They say that an eruption of Hawaiian-style runny lava from the Socorro magma body would present only moderate risk to humans; sticky lava would be much more dangerous. (Chapin and others)

Geoscientists think the uplift over the Socorro magma body has probably been going on this way for tens of thousands of years. (Fialko and Simons) If there is any change, they will know about it immediately. Over 800 seismometers  are in place around the magma body, and the area is also monitored by satellite and other means.

And while they are evaluating hazard, they are also learning more about volcanic processes in rift zones and about the complex but fascinating geological history of the Enchanted Land.

SOURCES:

Front page image from Back to the Bosque, New Mexico State University.

Chapin, C. E., Wilks, M., and McIntosh, W. C. 2004. Space­time patterns of Late Cretaceous to present magmatism in New Mexico—comparison with Andean volcanism and potential for future volcanism. New Mexico Bureau of Geology and Mineral Resources, Bulletin 160. Socorro, New Mexico.

Fialko, Y., and Simons, M. 2001. Evidence for on-going inflation of the Socorro magma body, New Mexico, from Interferometric Synthetic Aperture Radar imaging. Geophysical Research Letters, 28(18):3549–3552.

Mason, B. G., Pyle, D. M., and Oppenheimer, C. 2004. The size and frequency of the largest explosive eruptions on Earth. Bulletin of Volcanology, 66:735–748. Doi:10.1007/s00445-004-0355-9.

Zandt, G. April 25. CONFIRM Lecture 25: An overview of the collapse of the American Cordillera

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