As Pangea broke up and the plates drifted apart 200 million years ago, magma seeped out of the fissures in the Earth's crust. That magma became flows of lava, and that lava, rapidly cooling in the air and water, became the basalt now found in places like the United States' Northwest and East Coast.
Now, researchers say, those basalt formations could become a main depository for excess carbon dioxide. A study in this week's Proceedings of the National Academy of Sciences points out the advantages of using the East Coast's on- and offshore basalt flows for the sequestration of carbon dioxide captured from power plants in the region.
In carbon capture and sequestration (CCS), carbon dioxide from emitters like coal-fired plants would be compressed into a liquid state and pumped into underground reservoirs such as empty oil wells. The idea is to minimize the climate change-related effects of carbon dioxide emissions by keeping, as much as possible, the carbon released from formerly underground mineral deposits out of the carbon-overloaded atmosphere.
The PNAS study's authors, from Columbia University’s Lamont-Doherty Earth Observatory, say basalt — particularly offshore basalt — may be the ideal choice for a sequestration reservoir.
Basalt's advantages are several-fold. The igneous rock is full of tiny pores into which the liquefied carbon dioxide might be pumped. Once contained deep within the rock formations, the carbon dioxide would react with the basalt to form, over a relatively short time period, a carbonate mineral resembling limestone. This is expected to significantly decrease the risk of leakage, a major concern with previous CCS proposals that looked at shale and sandstone repositories.
“The basalt itself is very reactive, and in the end, you make limestone,” co-author Dennis Kent said. “It’s the ultimate repository.”
But even storing carbon in basalt is far from a perfect a solution to the world's fossil fuel-caused problems, some activists say.
"It's great that the science is advancing, but the fact is the science isn't going to be ready in time," says Greenpeace's Emily Rochon.
The Intergovernmental Panel on Climate Change says global emissions are going to need to peak in five to seven years to avoid the worst effects of climate change, she says, and CCS technologies will not be commercially ready until 2020 to 2030. She says the focus, rather, should be on reducing the burning of fossil fuels.
It is not clear how much time it would take to implement the Columbia team's basalt plan, still in the preliminary stages. The next step would be "to get some exploratory surveying and drilling going," said lead author David Goldberg, a geophysicist. The study suggests nine areas to start with.
The main point of the study is that basalt may be a superior alternative to other CCS plans. A plan to inject carbon dioxide from a coal-fired plant in Linden, N.J., for instance, has drawn criticism because it is not clear the sandstone into which it would pump would prevent the carbon dioxide from leaking out again.
But deep within the offshore basalt formations, the carbon dioxide would be too heavy, relative to the surrounding water, to come back up, in addition to the fact that it would become solidified into carbonate minerals — and would have hundreds of feet of marine sediment above it. As it fills in the porous interstices of the rock, the carbon dioxide is expected to displace only seawater.
Using seismic and gravity measures, the researchers found basalt formations offshore, four of which are more than 1,000 square kilometers each. A smaller patch off New Jersey's Sandy Hook, they say, contains enough basalt to hold a billion tons of carbon dioxide. A July 2008 study by the same researchers found that 208 billion metric tons could be stored in the offshore basalt formations of the U.S. Northwest's Juan de Fuca tectonic plate — that is as much as 150 years' worth of U.S. emissions.
The added advantage of the East Coast sequestration sites, which are off the coasts of New York, New Jersey, Massachusetts and states further south, is that they are relatively close to the region's metropolitan centers, making transport from those centers' power plants easier.
"The coast makes sense. That’s where people are. That’s where power plants are needed. And by going offshore, you can reduce risks,” Goldberg said.
Such a breakthrough would go a long way toward decreasing emissions.
In a study released Monday, ABI Research predicted that new CCS projects will keep 146 million tons of carbon dioxide out of the atmosphere. Their estimates are based on markets for carbon emissions allowances encouraging firms to seek out technologies like CCS to limit their emissions.
From 2009 through 2014, they predict, $14.6 billion will have been invested in 73 new CCS projects.
But Rochon worries that these projects will redirect funds that might be better spent on technologies like those used to generate renewable energy. The Waxman-Markey American Clean Energy and Security (ACES) bill passed by the U.S. House of Representatives in June, she points out, provides far more funding for CCS technologies than renewables.