Earthquakes shown to release some greenhouse gases

Science : Tetrafluoromethane (CF₄) is a greenhouse gas that persists in the atmosphere for 50 000 to 100 000 years. It is commonly produced by the weathering of granite and other metamorphic rocks by rainfall. Now Daniel Deeds of the US Geological Survey and his colleagues have discovered that CF₄ is also produced by tectonic activity. Surprised to find the chemical in groundwater samples collected near an active fault in the Mojave Desert, the researchers then examined 14 samples taken from aquifers along part of the San Andreas Fault. All but one of the samples showed higher CF₄ levels than did water that had been exposed to the air. That suggested the gas was being absorbed from stone deep underground. The researchers also found that the samples from closer to the fault had higher concentrations of the gas than did those from farther away. Whether the CF₄ is produced by the fracturing of rocks during earthquakes or by pressure stresses is not clear. However, the discovery that CF₄ levels are not exclusively tied to weathering means they are no longer a reliable indicator of past changes in climate.