Valerie Brown is to be congratulated for pursuing the
story line in “A Climate Change Solution?” that some of the
greenhouse carbon dioxide (CO2) that human activities are adding to
the atmosphere could possibly be sequestered deep within a stack of
basalt lava flows (HCN, 9/3/07). But the article
fails to describe how scientist Peter McGrail carried out his
laboratory experiments with basalt to get results labeled “pretty
close to serendipity.” The photo of McGrail holding a small vial of
powdered basalt suggests that he heated a mixture of this powder
and CO2 in a pressure vessel to get those results. If so, I find it
difficult to imagine how a similar result will occur by pumping CO2
down a 3,000-foot-deep well into massive basalt lava flows,
especially if small closed cavities (vesicles) in the basalt are to
be “… the targets of CO2 injection.”
As a professional
geologist who spent much of his career studying basalt, I find
Brown’s description of this most common of all volcanic rocks
lacking. For example, she writes “… minerals in the basalt,
principally calcium …” But calcium is simply one of many
elements in basalt; it is not a mineral,
although it can be a constituent of several different minerals. She
also writes that reactions between CO2 and basalt “… convert the
available elements into even more stable types of rock, such as
olivine.” But olivine is a mineral, not a rock,
and olivine occurs naturally in almost all basalt without any human
intervention.
Given its apparent lack of importance to
possible sequestration, undue emphasis is given to the columnar
structure present in some basalt. Moreover, while the large photo
of Devils Postpile in California illustrates such columns, why not
instead use a photo of one of the many highly photogenic examples
of basalt columns that are abundant within the Columbia River
basalt province, the very geographic focus for Brown’s article? And
why cite Wyoming’s Devils Tower as an example of columnar basalt,
when the rock of Devils Tower isn’t basalt … the rock described
as possibly “the holy McGrail of carbon sequestration.”
If HCN wants to educate readers about the
possibilities for CO2 sequestration in basalt, pertinent facts and
a tighter focus on the subject are desirable.
Wendell Duffield
Flagstaff, Arizona
Valerie Brown responds
I thank Dr. Duffield
for his close reading of my article. He is correct in regard to
calcium; it is an element, and I regret the error in describing it.
His other criticisms seem less instructive.
Dr. McGrail
told me that the results of his lab experiments with basalt and CO2
are being prepared for submission to a peer-reviewed journal. I
refer Dr. Duffield to the article cited in my piece, “Potential for
carbon dioxide sequestration in flood basalts” by B. Peter McGrail,
H. Todd Schaef, Anita M. Ho, Yi-Ju Chien, James J. Dooley, and
Casie L. Davidson; Journal of Geophysical
Research Vol. 111, B12202, doi:10.1029/ 2005JB004169,
2006, for an overview of the science and a statement of McGrail’s
hypothesis that carbonate minerals will form far more rapidly in
basalt than in sedimentary formations.
With respect to
the lab experiments, Dr. McGrail and his team are using a specially
customized high-pressure X-ray diffraction instrument that enables
them to observe the chemical reactions in real time so that they
can calculate the rate at which carbonate minerals are forming. The
basalt samples and the CO2 are placed in a small reactor cell and
subjected to temperatures and pressures similar to those that
prevail in the Grande Ronde formation of the Columbia River basalt
about 3,000 feet below the surface.
Dr. Duffield is
correct in saying that olivine is a mineral, but I think most
people would also consider it a rock.
I admit to waxing
lyrical about basalt’s columnar joining. That’s because it’s
beautiful, and High Country News deals with the
beauty, as well as the structure, of the natural world.
And Dr. Duffield is correct that some sources refer to Devils Tower
as phonolite, an igneous rock closely related to, and often
intermixed with, basalt. But even academic geologists refer to
Devils Tower as basalt occasionally. (See Growth,
Dissolution and Pattern Formation in Geosystems, Bjorn
Jamtveit and Paul Meakin, eds., Kluwer Academic Publishers, 1999,
p. 11: “The highlight of this chapter, from a geological point of
view, is an analysis of the origin of fracture patterns in columnar
basalt such as the Giant’s Causeway in County Antrim, Northern
Ireland and the Devils Tower in Wyoming.”)
This article appeared in the print edition of the magazine with the headline Fault lines.
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