AGU journal highlights -- July 2, 2009

1. Ancient supervolcano's eruption caused decade of severe winters

Previous studies have suggested that Indonesia's Toba supervolcano, when it erupted about 74,000 years ago, triggered a 1,000-year episode of ice sheet advance, and also may have produced a short-lived "volcanic winter," which drastically reduced the human population at the time. Previous climate model simulations of the eruption have been unable to produce the glaciation, and there are no climate observations to support the volcanic winter. To investigate additional mechanisms that may have enhanced and extended the effects of the Toba eruption, as well as the volcanic winter, Robock et al. conduct six climate model simulations using state-of-the-art models that include vegetation death effects on radiation budgets, and stratospheric chemistry feedbacks that might affect the lifetime of the volcanic cloud. The authors use a wide variety of aerosol injection volumes, ranging from 33 to 900 times that of the 1991 Mount Pinatubo injection. They find that none of the models initiate glaciation. Nonetheless, they produce a decade of severe volcanic winter, which would likely have had devastating consequences for humanity and global ecosystems, supporting the idea that the Toba eruption produced a genetic bottleneck in human evolution.

Title: Did the Toba volcanic eruption of ~74 ka B.P. produce widespread glaciation?

Authors: Alan Robock and Georgiy Stenchikov: Department of Environmental Sciences, Rutgers University, New Brunswick, New Jersey, USA;

Caspar M. Ammann and Samuel Levis: National Center for Atmospheric Research, Boulder, Colorado, USA;

Luke Oman: Department of Earth and Planetary Sciences, The Johns Hopkins University, Baltimore, Maryland, USA;

Drew Shindell: NASA Goddard Institute for Space Studies, New York, New York, USA.

Source: Journal of Geophysical Research-Atmospheres (JGR-D) paper 10.1029/2008JD011652, 2009; http://dx.doi.org/10.1029/2008JD011652

2. Understanding fault movement during Wenchuan earthquake

The magnitude 7.9 earthquake on 12 May 2008 in Wenchuan, China, killed more than 87,000 people, injured 370,000, and caused extensive damage. Because some areas in the fault zone were inaccessible, scientists did not immediately have a detailed understanding of the fault movement during this event. To learn more, Hao et al. combine field investigations of the Longmen Shan fault zone with satellite observations to obtain details of the crustal deformation over the entire fault zone. They also create a model to simulate the motion of the fault zone. The model shows that thrust fault slips were dominant along the segment of the Yingxiu-Beichuan fault near the epicenter, while dextral fault slips dominated along the northeast segment of that fault. On the basis of observations and simulations, the authors conclude that the simultaneous ruptures of the Yingxiu-Beichuan and Guanxian-Anxian faults caused the Wenchuan earthquake. The results should improve scientists' understanding of the motion of the Longmen Shan fault zone during this disastrous earthquake.

Title: Coseismic surface-ruptures and crustal deformations of the 2008 Wenchuan earthquake Mw7.9, China