In an 1889 travel article, the New York Times waxed enthusiastic about a nearby but, it said, little visited attraction: "the wondrous Palisades…. basaltic precipices of the Hudson." Rising on the west side of the lower Hudson River for 20 miles in New Jersey and New York, the towering Palisades are actually the visible remnants of enormous floods of magma that flowed hot about 200 million years ago, cooling into a vast expanse of basalt that extends to Europe, Africa and South America, much of it buried deep under the Atlantic Ocean. 

Early Dutch New Yorkers called the staircase-like basalt of the Palisades "trap rock"; not because it trapped anything, but after their native word for "step". But a new scientific analysis suggests that the related basalt formations buried under the U.S. east coast and extending out to sea might someday be doing some critical trapping after all—of greenhouse gas emissions from the likes of giant coal-burning power plants. 

The analysis, published this month in the Proceedings of the National Academy of Sciences, suggests that expanses of basalts along and just beyond the heavily populated east coast might be ideal for locking-up billions of tons of carbon dioxide (CO2). 

Advocates of "clean coal" technology see carbon sequestration—capturing and then storing CO2 deep underground—as a way for the world to keep burning the cheap and abundant fossil fuel without aggravating global warming. Whether carbon capture and storage will ever turn out to be economically or environmentally feasible remains open to often-fierce debate. But the prospect of injecting CO2 into basalt formations could at least resolve one major fear: that the gas might eventually escape to the surface. 

The Ultimate Repository

Basalt, it turns out, is capable of performing what seems like sheer alchemy: It can transform normally buoyant CO2 dissolved in water into something decidedly non-buoyant—solid rock. Essentially, a series of chemical reactions combines carbon dioxide with calcium in the basalt to form calcium carbonate, or limestone. 

Dennis Kent, a professor of geological sciences at Rutgers University, and one of three co-authors of the study, says that transformation from gas to solid could make basalt formations "the ultimate repository" for excess carbon. 

Although the report notes that some basalt formations on land might suffice as storage sites, the deeper formations under sea beds could be particularly attractive when it comes to preventing CO2 from escaping, according to study co-author David Goldberg, a geophysicist at Columbia University's Lamont Doherty Earth Observatory. 

Hundreds or even thousands of feet of sediment can lie atop undersea basalt formations. In addition to a thick cap of solid basalt that would lie above any suitable deeper injection site, those thick blankets of sediment could serve as an additional impermeable cap during the years the CO2 was becoming mineral. (Research has yet to fully detail just how long it would take for a volume of CO2 to transform into rock.) 

The new study points to an array of expansive east coast basalt formations, including four undersea of more than 380 square miles each off New Jersey, New York, and Massachusetts, as well as large formations on land and under the seas in and around Georgia and South Carolina. 

Globally, potential for carbon storage in formations of basalt and other "ultramafic" rocks (those with minerals that react with carbon dioxide to form more minerals) could be enormous. Goldberg and Columbia scientist Angela Slagle have estimated that basalt formations under oceans worldwide alone have the potential to store tens of trillions of tons of CO2. 

According to the analysis, a single formation buried under the coastline near Sandy Hook, N.J., just south of the city of New York, could store 900 million tons of CO2, or 40 years of emissions from three to four large coal-burning power plants, although the report also notes that a great deal of research, including drilling to map and characterize formations, still lies ahead. 

Elsewhere in Europe, the U.S. and the Middle East, research on whether basalt and similar formations can indeed offer a safer pathway to carbon storage is accelerating. 

Real-World Testbeds

Until recently, the only real-world attempts to study basalt injection have been small experiments in test wells in the Pallisades rock by Columbia geochemist Juerg Matter and fellow scientists. But beginning in February, Matter and a team of researchers from France and Iceland plan to kick off a larger-scale pilot project at a geothermal power plant owned by Reykjavik Energy. (In this case, the CO2 isn't a by-product of combustion, but comes up from underground as traces of geothermal gas in the huge volumes of steam that provide most of Iceland's heat and electric power.) 

Over about nine months, the "CarbFix" project will inject about 2000 tons of CO2 into a 2000 foot hole bored into an island that itself is more than 90 percent basalt. According to Matter, the researchers will use additional holes drilled a few hundred yard away to monitor changes in groundwater, which should show how effectively and quickly chemical reactions are occurring. 

Meanwhile, in the United States, environmental engineer B.P. "Pete" McGrail, at the U.S. Department of Energy's Pacific Northwest National Laboratory, reports that his team has completed drilling and prep work for another experimental project to inject about 1000 tons of CO2 into a basalt formation under the southeastern corner of the state of Washington. McGrail is waiting for permits to be finalized, but noted in an email, "If our permit is approved, CO2 injection would occur sometime this summer." 

McGrail says he concurs with the new report's suggestion that undersea basalt formations could someday become major repositories for carbon, but suggested that "those opportunities would develop later down the road after pilot and commercial studies show feasibility in terrestrial settings." 

Basalt isn't the only rock that reacts with carbon dioxide. As PM reported in 2008, Columbia's Peter Kelemen continues to investigate the potential for a type of rock called peridotite, not only to lock-up carbon captured from the likes of power plant emissions, but even to yank volumes of the greenhouse gas directly out of the atmosphere, with some help from water and heat from the earth's interior. 

Notably, about half the nation of Oman lies atop formations of this rock. If it turns out to work, what Kelemen calls "air capture" could effectively help neutralize, as he told us, the "substantial portion of CO2 that comes from places where we wouldn't have any hope of capturing it—CO2 emitted by cars, for example."