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American Geophysical Union
AGU journal highlights -- Jan. 7, 2014 The following highlights summarize research papers that have been recently published in Geophysical Research Letters (GRL) and Water Resources Research (WRR).
In this release:
Kīlauea magma chamber inflation triggered strong 2007 earthquakes Seal-borne sensors are valuable for studies of Southern Ocean conditions Laboratory experiments examine earthquake precursors Tree ring records reconstruct streamflow variability in northern Utah Chain reaction drainage of supraglacial lakes led to breakup of Larsen B Ice Shelf Improving estimates of greenhouse gas emissions from lakes
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1. Kīlauea magma chamber inflation triggered strong 2007 earthquakes
Hawaii's Kīlauea volcano has been erupting since 1983. Starting in 2003, researchers noticed an inflation of the magma chamber beneath the volcano, an inflation that accelerated in 2006. In June 2007, the volcano's eruption peaked with a burst of activity known as the Father's Day event. In the buildup to the Father's Day eruptions, according to new research by Wauthier et al., a pair of large-magnitude earthquakes hit, with an epicenter beneath the volcano. Earthquakes are common around the volcano, which sits on Hawaii's Big Island, but with magnitudes of 4.7 and 4.1, the two 2007 earthquakes were among the most powerful recorded in the region since records began in 1959.
Most volcano-tectonic earthquakes have very small magnitudes, and no known mechanisms exist to explain the powerful Kīlauea earthquakes. Analyzing a range of seismic and geodetic data, the authors suggest that the large-magnitude quakes were caused when inflation in the magma chamber beneath Kīlauea caused preexisting faults to slip. The authors suggest that a similar mechanism could play out at other volcanoes worldwide.
Source:
Geophysical Research Letters, doi:10.1002/2013GL058082, 2013
http://onlinelibrary.wiley.com/doi/10.1002/2013GL058082/abstract
Title:
Moderate-magnitude earthquakes induced by magma reservoir inflation at Kīlauea Volcano, Hawai'i
Authors:
Christelle Wauthier and Diana C. Roman: Department of Terrestrial Magnetism, Carnegie Institution of Washington, USA;
Michael P. Poland: Hawaiian Volcano Observatory, USGS, Hawaii, USA.
2. Seal-borne sensors are valuable for studies of Southern Ocean conditions
Icy conditions make it difficult to monitor the southern part of the Southern Ocean using floats or ship-based sampling. For about a decade scientists have been mounting temperature and salinity sensors on the heads of seals from several colonies around Antarctica. There is now a fairly large data set of seal-derived hydrographic data.
Roquet et al. sought to determine how valuable these data are in studying ocean conditions. They conducted two numerical ocean circulation experiments, one using data from a global network of floats to constrain the model and one also using seal-based data. The only difference between the two experiments was the inclusion of the seal-based data.
The authors find that including the seal-derived data modified the estimated circulation patterns and improved the model's agreement with satellite data on sea ice concentrations. They conclude that sensors mounted on animals can provide a valuable contribution to monitoring polar conditions.
Source:
Geophysical Research Letters, doi: 10.1002/2013GL058304, 2013
http://onlinelibrary.wiley.com/doi/10.1002/2013GL058304/abstract
Title:
Estimates of the Southern Ocean general circulation improved by animal-borne instruments
Authors:
Fabien Roquet and Leon Chafik: Department of Meteorology, Stockholm University, Stockholm, Sweden;
Carl Wunsch: Department of Earth and Planetary Sciences, Harvard University, Cambridge, Massachusetts, USA;
Gael Forget and Patrick Heimbach: Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, Massachusetts, USA;
Christophe Guinet and Frederic Bailleul: Centre d'Etudes Biologiques de Chizé, Centre National de la Recherche Scientifique, Villiers en Bois, France;
Gilles Reverdin and Jean-Benoit Charrassin: Laboratoire d'Océanographie et du Climat: Expérimentation et Approches Numériques, Paris, France;
Daniel P. Costa, Luis A. Huckstadt and Kimberly T. Goetz: Department of Ecology and Evolutionary Biology, University of California, Santa Cruz, California, USA;
Kit M. Kovacs, Christian Lydersen, Martin Biuw and Ole A. Nøst: Norwegian Polar Institute, Tromsø, Norway;
Horst Bornemann and Joachim Ploetz: Alfred-Wegener-Institut, Helmholtz Zentrum für Polar- und Meeresforschung, Bremerhaven, Germany;
Marthan N. Bester and Trevor McIntyre: Mammal Research Institute, Department of Zoology and Entomology, University of Pretoria, Pretoria, South Africa;
Monica C. Muelbert: Instituto de Oceanografia, Universidade Federal do Rio Grande, Porto Alegre, Brazil;
Mark A. Hindell and Clive R. McMahon: Institute for Marine and Antarctic Studies, University of Tasmania, Hobart, Tasmania, Australia;
Guy Williams: Antarctic Climate & Ecosystems Cooperative Research, University of Tasmania, Hobart, Tasmania, Australia;
Robert Harcourt and Iain C. Field: Marine Predator Research Group, Department of Biological Sciences, Macquarie University, Sydney, New South Wales, Australia;
Keith W. Nicholls: British Antarctic Survey, Natural Environment Research Council, Cambridge, UK;
Lars Boehme and Mike A. Fedak: Sea Mammal Research Unit, Scottish Oceans Institute, University of St Andrews, St Andrews, UK.
3. Laboratory experiments examine earthquake precursors
Although it is not possible to predict when an earthquake will occur, many earthquakes have been found to have had some precursor activity. To study precursors of stick-slip behavior, Johnson et al. conducted laboratory experiments on a sheared granular material under normal stress ranging from 2 to 8 megapascals (290 to 1,160 pounds per square inch) as an analog for a fault under tectonic stress. They find that acoustic emissions and microslips are a precursor to larger movements. Very similar results are obtained in a discrete element simulation of sheared beads. These types of experiments could help scientists better understand when earthquakes are more likely to occur. As shown by a number of researchers, very similar activity preceding faulting can occur in the Earth.
Source:
Geophysical Research Letters, doi:10.1002/2013GL057848, 2013
http://onlinelibrary.wiley.com/doi/10.1002/2013GL057848/abstract
Title:
Acoustic emission and microslip precursors to stick-slip failure in sheared granular material
Authors:
P. A. Johnson, R. A. Guyer, P-Y. Le Bas and D. T. Trugman: Los Alamos National Laboratory, Geophysics Group, Los Alamos, USA;
B. Kaproth, M. Scuderi and C. Marone: Department of Geosciences, Pennsylvania State University, University Park, Pennsylvania, USA;
B. Ferdowsi and J. Carmeliet: Swiss Federal Institute of Technology Zürich (ETHZ) - DBAUG, Schafmattstrasse 6, CH-8093 Zürich, Switzerland; and Swiss Federal Laboratories for Materials Science and Technology (Empa), Dübendorf (Zürich), Switzerland;
M. Griffa: Swiss Federal Laboratories for Materials Science and Technology (Empa), Dübendorf (Zürich), Switzerland.
4. Tree ring records reconstruct streamflow variability in northern Utah
People in northern Utah, including Salt Lake City, depend on water stored as winter snow and delivered by mountain streams to populated areas. Climate models predict that in the near future, warmer temperatures will lead to a decrease in winter snow and streamflow in mountain streams, possibly leading to water shortages for the region.
To gain a longer-term perspective on water availability, it is helpful to have a record of past streamflow variability, but streamflow records are generally limited to relatively short term instrumental records. Allen et al. reconstructed streamflow in the Logan River—a main tributary of the Bear River that is the main source of inflow to the Great Salt Lake—for the past several centuries, going back to 1605. Their reconstruction, based on tree ring records from Douglas fir, pinyon pine, and Rocky Mountain juniper trees, indicates that streamflow was more variable, with more extreme droughts and floods, over the past several centuries than in the recent instrumental record. The authors suggest that water resources managers should take this higher variability into account when planning water management strategies.
Source:
Water Resources Research, doi: 10.1002/2013WR014273, 2013
http://onlinelibrary.wiley.com/doi/10.1002/2013WR014273/abstract
Title:
A tree-ring-based reconstruction of Logan River streamflow, northern Utah
Authors:
Eric B. Allen: Department of Geology, Utah State University, Logan, Utah, USA;
Tammy M. Rittenour: Associate Professor, Department of Geology, Utah State University, Logan, Utah, USA;
R. Justin DeRose: Research Ecologist, Forest Inventory and Analysis, Rocky Mountain Research Station, Ogden, Utah, USA;
Matthew F. Bekker: Associate Professor, Department of Geography, Brigham Young University, Provo, Utah, USA;
Roger Kjelgren: Professor, Department of Plant, Soils, and Climate, Utah State University, Logan, Utah, USA;
Brendan M. Buckley: Lamont Associate Research Scientist, Tree Ring Laboratory, Lamont-Doherty Earth Observatory, New York, USA.
5. Chain reaction drainage of supraglacial lakes led to breakup of Larsen B Ice Shelf
In 2002, Antarctica's Larsen B Ice Shelf disintegrated over the course of just a few months. The shelf, which covered more than 3000 square kilometers (1158 square miles) of ice, had been stable for thousands of years before it broke up, and the processes involved in the sudden breakup were not well understood. Before the breakup, there were more than 2700 small supraglacial lakes on top of the ice shelf that had formed as ice melted gradually over the preceding years. Observations indicated that the majority of those lakes drained within the final few days before the ice shelf broke up, but scientists were not certain how that could have happened.
Now, using a simulation of the stresses that the lakes create on the ice shelf, Banwell et al. show that the draining of one supraglacial lake could result in fractures under other lakes, which, in turn, could cause more fractures under more lakes and thus cause numerous lakes to drain, in a chain reaction. The draining of many supraglacial lakes in a short time period ultimately led to the breakup of the entire ice shelf, the authors suggest.
Source:
Geophysical Research Letters, doi:10.1002/2013GL057694, 2013
http://onlinelibrary.wiley.com/doi/10.1002/2013GL057694/abstract
Title:
Breakup of the Larsen B Ice Shelf triggered by chain reaction drainage of supraglacial lakes
Authors:
Alison F. Banwell: Department of Geophysical Sciences, University of Chicago, Chicago, Illinois, USA; and Scott Polar Research Institute, University of Cambridge, Cambridge, UK;
Douglas R. MacAyeal: Department of Geophysical Sciences, University of Chicago, Chicago, Illinois, USA;
Olga V. Sergienko: The Atmospheric and Oceanic Sciences Program, Princeton University, Princeton, New Jersey, USA.
6. Improving estimates of greenhouse gas emissions from lakes
Lakes emit carbon dioxide and methane and are thus an important part of global climate. Many estimates of emissions for individual lakes are based on a measurement from a single location within the lake, but, as Schilder et al. point out, emissions can vary across the lake. They collected methane and carbon dioxide measurements at several locations for each of 32 lakes in Europe, and find that estimates based only on near-shore measurements tend to underestimate diffusive emissions, while those based only on center-lake locations tend to overestimate emissions. The study provides a method to improve estimates of greenhouse gas emissions from lakes.
Source:
Geophysical Research Letters, doi:10.1002/2013GL057669, 2013
http://onlinelibrary.wiley.com/doi/10.1002/2013GL057669/abstract
Title:
Spatial heterogeneity and lake morphology affect diffusive greenhouse gas emission estimates of lakes
Authors:
Jos Schilder, Maarten van Hardenbroek, Päivi Rinta, Tabea Stötter and Oliver Heiri: Institute of Plant Sciences and Oeschger Centre for Climate Change Research, University of Bern, Bern, Switzerland;
David Bastviken: Department of Thematic Studies-Water and Environmental Studies, Linköping University, Linköping, Sweden;
Paula Kankaala: Department of Biology, University of Eastern Finland, Joensuu, Finland.
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Contact:
Nanci Bompey
Phone (direct): +1 202 777 7524
E-mail: nbompey@agu.org
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