Carbon dioxide sequestration in basalt involves the injecting of  into deep-sea formations. The  first mixes with seawater and then reacts with the basalt, both of which are alkaline-rich elements. This reaction results in the release of  and  ions forming stable carbonate minerals.
Underwater basalt offers a good alternative to other forms of oceanic carbon storage because it has a number of trapping measures to ensure added protection against leakage. These measures include "geochemical, sediment, gravitational and hydrate formation." Because  hydrate is denser than  in seawater, the risk of leakage is minimal. Injecting the  at depths greater than  ensures that the  has a greater density than seawater, causing it to sink.
One possible injection site is Juan de Fuca plate. Researchers at the Lamont–Doherty Earth Observatory found that this plate at the western coast of the United States has a possible storage capacity of 208 gigatons. This could cover the entire current U.S. carbon emissions for over 100 years.
This process is undergoing tests as part of the CarbFix project, resulting in 95% of the injected 250 tonnes of CO to solidify into calcite in two years, using 25 tonnes of water per tonne of CO.