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Plant Response to CO2 Escaping from Fractures and Faults of Active Volcanic Systems
Houlie, N., Komorowski, J.C., de Michele, M., Kasereka, M. and Ciraba, H. 2006. Early detection of eruptive dykes revealed by normalized difference vegetation index (NDVI) on Mt. Etna and Mt. Nyiragongo. Earth and Planetary Science Letters 246: 231-240.

What was done
Using high-resolution multi-spectral data acquired by the Advanced Spaceborne Thermal Emission and Reflection (ASTER) radiometer on the Terra satellite viewing Mount Etna (Italy), as well as the high-resolution multi-spectral IKONOS instrument viewing Mount Nyiragongo (Democratic Republic of Congo), the authors documented "for the first time," as they describe it, "the existence of a strong link between pre-eruptive activity, the growth of vegetation on the volcano's active rift zones, and the location of likely future eruptive activity."

What was learned
On Mt. Etna, Houlie et al. detected an elevated NDVI [normalized difference vegetation index] signal on ASTER data with a width of 60 m and a length of about 3 km just north of the Pernicana fault in the North East Rift Zone, noting that "the NDVI signal [was] markedly visible for up to 2 years before the eruption on images taken in the same season in 2002 and 2003." Likewise, on a pre-eruptive 2001 IKONOS satellite image of Mt. Nyiragongo, they observed an NDVI signal with a width of 20 m that extended over a length of about 4 km on the flank-fissure system that became eruptive in 2002, as well a second such feature with a width of 20 m that extended about 1.5 km.

What it means
The five researchers state that the "anomalous elevated NDVI signal and the excessive photosynthetic activity it implies cannot be reconciled except by the combined role of subsurface enhanced heat flux, flux of CO2, and associated water condensation along a structural trend," although they later downplay the roles of heat and water. If they have any qualms about the role of CO2 in stimulating plant growth along the fault lines, it is that there might be too much of it. However, they state that "routine monitoring by staff of the Goma Volcano Observatory gives values between 2 and 6 vol.% [20,000 to 60,000 ppm] for the atmospheric concentration of CO2 directly inside the 2002 eruptive fractures where a relict moderate heat flux is present and where vegetation has been developing very well since the eruption [our italics]." Once again, therefore, we have a new set of situations where earth's vegetation has been demonstrated to positively respond to Very High CO2 Concentrations.

Reviewed 27 September 2006