AGU Journal Highlights -- Aug. 14, 2007

Title: An observational case study of mesoscale atmospheric circulations induced by soil moisture

Authors: Christopher M. Taylor and Phil P. Harris: Centre for Ecology and Hydrology, Wallingford, U.K.;

Douglas J. Parker: Institute for Atmospheric Science, School of Earth and Environment, University of Leeds, Leeds, U.K.

Source: Geophysical Research Letters (GRL) paper 10.1029/2007GL030572, 2007

7. Dehydration of water-bearing minerals helps to lubricate faults

Accurate seismic hazard assessments depend on deep knowledge of fault dynamics and motion during earthquakes. Scientists must understand the mechanical properties of faults, especially at the fast slip rates that occur in earthquakes. Although theoretical studies in major fault zones suggest that faults might be weak during large earthquakes, laboratory experiments and deep borehole measurements worldwide show that average stresses in the crust must be generally high. Noting that hydrous minerals such as serpentine are common in mature fault zones, Hirose and Bystricky conducted high-velocity friction experiments on simulated faults in serpentinite at earthquake slip conditions. They find that the fault strength dramatically decreases due to rapid heating produced by fast slip rates. They hypothesize that the rapid heating separates hydroxyl ions (OH-) from the serpentine mineral structure, forming water. This free water helps to lubricate the fault plane. The authors expect that this fault-weakening mechanism may explain the lack of pronounced heat flow in major faults such as the San Andreas.

Title: Extreme dynamic weakening of faults during dehydration by coseismic shear heating

Authors: Takehiro Hirose: Department of Geology and Mineralogy, Graduate School of Science, Kyoto University, Kyoto, Japan; currently at Istituto Nazionale di Geofisica e Vulcanologia, Roma, Italy;

Misha Bystricky: LMTG, Université de Toulouse, CNRS, IRD, Observatoire Midi-Pyrénées, Toulouse, France.

Source: Geophysical Research Letters (GRL) paper 10.1029/2007GL030049, 2007

8. Climate change and geoengineering: Is the cure worse than the sickness?

Global warming occurs when greenhouse gases, such as carbon dioxide from burning fossil fuels, build up in the atmosphere and alter outgoing longwave radiation. Some scientists have proposed that mitigating global warming could be accomplished by emulating a volcanic eruption because volcanic aerosols scatter incoming sunlight, reducing outgoing radiation. Trenberth and Dai caution against this mitigation proposal. They examine precipitation and streamflow records from 1950 to 2004 to document the effects of volcanic eruptions from Mexico's El Chichón (1982) and the Philippines’ Pinatubo (1991). They find that, following the 1991 eruption of Mount Pinatubo, there was a substantial global decrease in precipitation over land, a record decrease in runoff and river discharge into the oceans, and widespread drying over land during the following year. Thus, the authors conclude that major adverse effects, including drought, could arise from geoengineering solutions to global warming.

Title: Effects of Mount Pinatubo volcanic eruption on the hydrological cycle as an analog of geoengineering