Global warming, the result of high concentrations of greenhouse gases trapping heat in the atmosphere that would normally have escaped into space, presents a complex problem.
One possible approach, carbon sequestration, involves capturing carbon dioxide that would be emitted by industrial processes and storing it where it would be unlikely to be released into the atmosphere. This would help reduce carbon-dioxide emissions, slowing down the pace of climate change.
Researchers at the Lamont-Doherty Earth Observatory in New York, who have been working to identify possible storage sites, have found some possible candidate off the Eastern Seaboard.
"We are primarily looking for basalt lava flows that extend off shore," David Goldberg, a researcher at Lamont-Doherty, said. Basalt lava flows are artifacts of prehistoric volcanic activity; they can be found on land and at sea.
"These are good potential reservoirs for carbon dioxide storage because they have open porosity and permeability in the flow tops, are buried by thousands of feet of impermeable sediments, and geochemically convert carbon dioxide to solid carbonate over time," Goldberg said.
The porous and permeable tops of a basalt lava flow allow for injection of carbon dioxide, while the sediments on top of the flows prevent the carbon dioxide from escaping.
Furthermore, carbon dioxide can react with basalt to form stable, nontoxic carbonates, which further reduces the risk of leakage.
Goldberg's team of researchers has been searching for and testing basalt lava flows near the Eastern Seaboard.
"To a large extent we used previously published research," Goldberg said. "Some was from offshore geophysical surveys, drill and coring results, as well as surface geology maps."
In particular, they focused on the Central Atlantic Magmatic Province, a seismic region with abundant basalt flows. They sought to find basalt flows deep enough underwater for practical carbon sequestration.
"We suggest large potential lava flows extend off shore, and if proven, their properties are likely to reflect the properties of similar lava flows that have been observed and measured on shore," Goldberg said. "The basalt extent is potentially large enough to accommodate significant volumes of carbon dioxide along the East Coast."
Four regions in particular look promising: the Newark Rift Basin, the New York Bight, the Sandy Hook basin and the South Georgia Rift Basin.
Scientists have begun small-scale experiments at the Newark Rift Basin. In one experiment, conducted at the Palisades Sill, scientists injected dissolved carbon dioxide into the basalt flow and monitored the results. Then, 200 after injection, water samples showed decreases in the concentration of calcium and magnesium ions, suggesting that these ions had reacted with the carbon dioxide to form carbonates.
Core samples taken from Orange Mountain, a basalt formation in New Jersey, show that basalt flows in the Newark Rift Basin are porous enough for carbon dioxide injection.
While the New York Bight and Sandy Hook basin have not been tested for basalt flows, they both have significant amounts of sedimentation. Models of these regions suggest the presence of basalt flows deep beneath the sediments.
If these are present, Goldberg's team estimates that, in the Sandy Hook basin alone, as much as 900 million tons of carbon dioxide - the equivalent of 40 years of emissions from four coal plants - could be stored.
Stretching from beneath the coastal plains of Georgia and South Carolina, the South Georgia Rift Basin is the largest rift basin on the Eastern Seaboard. Given its extent it could be a tremendously valuable carbon sequestration site.
Now that they have identified some candidate sites, David and his coworkers have their work cut out. "The next steps are to conduct detailed geophysical surveying, both on shore and offshore, to identify basalt flows as research targets, then, test core samples to verify their basic properties and compositions," Goldberg said.
"It is probably most efficient to survey and core on shore first, then move to offshore locations. Ultimately a pilot carbon dioxide injection experiment similar to those being conducting in Washington State and in Iceland would be envisioned."
