June GEOLOGY highlights
Boulder, Colo. – The June issue of GEOLOGY covers a wide variety of potentially newsworthy subjects. Topics include: new evidence for an extended winter scenario following the K-T boundary event; atmospheric and tectonic forces that shaped Archean climate evolution; natural changes in the sea floor as a cause of coastal erosion; the relationship between Earth's rotational axis and low seasonal temperature ranges of the early Paleogene; evidence for a late Holocene earthquake in northern Puget Sound; and additional evidence for a Tacoma fault in Washington's Puget lowland.
Highlights are provided below. Representatives of the media may obtain complimentary copies of articles by contacting Ann Cairns at [email protected]. Please discuss articles of interest with the authors before publishing stories on their work, and please make reference to GEOLOGY in articles published. Contact Ann Cairns for additional information or other assistance.
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Methane emission from mud volcanoes in eastern Azerbaijan
Giuseppe Etiope, National Institute of Geophysics and Volcanology, Rome, Italy, et al. Pages 465-468.
This paper presents the results of the first detailed study (carried out in May 2003) of methane flux from mud volcanoes in eastern Azerbaijan, the territory with the world's largest mud volcanoes and the densest mud volcano population. Although the phenomenon of mud volcanism has being studied extensively in the past years, the importance of the global gas emission from mud volcanoes in the atmosphere budget and climate change remains uncertain mainly because of the lack of reliable direct flux measurements. The results presented in our paper imply that mud volcanoes emit significant amounts of greenhouse gas (methane) into the atmosphere, and this previously unrecognized source is comparable (by size) with other anthropogenic and natural sources of methane. This new finding opens a wide window of opportunity for geoscientists and atmosphere scientists and calls for additional measurements of gas flux from around the world to better constrain the contribution of mud volcanoes to the global sources of methane in the atmosphere.
Land-level changes from a late Holocene earthquake in the northern Puget lowland, Washington
Harvey Kelsey, Humboldt State University, Department of Geology, Arcata, CA 95521, U.S.A., et al. Pages 469-472.
A magnitude 6.5–7 earthquake struck the northern Puget Sound (Washington) area ca. 3000 years ago, resulting in abrupt uplift of the ground surface. The earthquake was discovered by geologists Harvey Kelsey (Humboldt State University, Arcata, California) and Brian Sherrod (U.S. Geological Survey) while investigating the record of sea level rise at coastal marshes on central Whidbey Island. The geologists noted that sea level abruptly dropped at one marsh relative to the other ca. 3000 years ago, which was odd because the two marshes are only a few miles from each other. Following up on a hunch that the reason for odd sea level behavior was an earthquake, Kelsey and Sherrod teamed up with coauthors Sam Johnson and Shawn Dadisman of the U.S. Geological Survey; these two marine geologists looked for evidence of the earthquake in seismic records in the ocean floor just offshore of the marshes. Johnson and Dadisman found that a fault, which probably caused the earthquake, cuts the seafloor and runs right between the two marshes. Kelsey and colleagues discovery of a prehistoric earthquake 3000 years ago in the northern Puget lowland is doubly shaky. That is, the region not only is prone to seismic shaking from subduction zone earthquakes offshore but also from magnitude 6.5–7 earthquakes that will let loose right beneath your feet, if your feet are standing somewhere in the urbanized coastal corridor from Everett, Washington north to the Canadian border.
Less ice, less tilt, less chill: The influence of a seasonally ice-free Arctic Ocean and reduced obliquity on early Paleogene climate
Jacob Sewall and Lisa Sloan, University of California, Santa Cruz, Earth Sciences, Santa Cruz, CA 95064, U.S.A. Pages 477-480.
The early Paleogene is a time in Earth's history that extends from 65 to 45 million years before present. Earth's climate during the early Paleogene was markedly different from Earth's climate today. Notable features of early Paleogene climate include polar temperatures that were significantly warmer than today (early Paleogene crocodiles have been found near Greenland) and seasonal temperature ranges in the centers of large continents (for example, Siberia and mid-western North America) that resemble the temperature ranges currently found in coastal California or Japan. For over twenty years, climate scientists have searched for the mechanism through which such a low range of seasonal temperatures could be achieved. Our climate modeling experiments suggest that the low seasonal temperature ranges of early Paleogene continental interiors can be achieved by reducing the tilt of Earth's rotational axis. When this reduced axial tilt is combined with increased global warmth from high greenhouse gas concentrations, our modeled early Paleogene climate matches climate data from the early Paleogene quite well.
Modeling ocean floor spreading rates through time: The matrix reloaded
Robert Demicco, State University of New York, Binghamton, Department of Geological Sciences and Environmental Studies, Binghamton, NY 13902-6000, U.S.A. Pages 485-488.
This paper sets up a procedure for modeling seafloor generation and destruction. The model is very general and allows for a variety of scenarios of crust production and destruction that can account for the present-day distribution of seafloor.
Experimental constraints on magma ascent rate for the Crater Flat volcanic zone hawaiite
Mike Nicholis and Malcolm Rutherford, Brown University, Geological Sciences, Providence, Rhode Island 02912, U.S.A.. Pages 489-492.
One of the fundamental processes that control the style and magnitude of volcanic eruptions is the rate at which magma ascends to surface. Magma ascent rates are a function of both the volatile content and magma composition. In this study the volatile content for the hawaiitic magma composition erupted in the Crater Flat volcanic zone, located near Yucca Mountain, was constrained and used to experimentally determine magma ascent rates. A series of experiments was designed to simulate magma ascent in the Crater Flat volcanic zone. Crystal growth was quantified and compared in both natural rocks and experimental products to extract minimum values for magma ascent in the region. This data can be used in models that evaluate the magnitude of potential volcanic hazards.
Geologic evidence for Archean atmospheric and climatic evolution: Fluctuating levels of CO2 , CH4 , and O2 with an overriding tectonic control
Donald Lowe and Michael Tice, Stanford University, Department of Geological and Environmental Sciences, Stanford, CA 94305-2115, U.S.A. Pages 493-496.
The atmosphere and climate of early Earth, before 2.5 billion years ago, were fundamentally different than they are today. Before 3.2 billion years, Earth's surface and early life forms were probably roasting at a temperature of nearly 70 °C resulting from an effective carbon dioxide and methane greenhouse. Evolution of the first large blocks of continental crust 3.2–3.0 billion years ago caused the collapse of this early greenhouse through depletion of carbon dioxide by weathering and, eventually, of methane by formation of atmospheric haze. These events appear to have culminated in glaciation at 2.9 billion years. Eventually, reduced weathering and recycling of carbon dioxide saw the return of warm to hot greenhouse conditions after 2.7 billion years. A similar cycle of greenhouse collapse was initiated by formation of large new tracts of continental crust at about 2.7–2.5 billion years ago.
Long-term glacial erosion of active mountain belts: Example of the Chugach-St. Elias Range, Alaska
Jim Spotila, Virginia Tech, Geosciences, Blacksburg, Virginia 24061, U.S.A., et al. Pages 501-504.
The Chugach-St. Elias Range in southern Alaska exhibits the highest coastal relief and fastest short-term erosion rates on Earth. This mountain building is driven by micro-continental collision and facilitated by the erosive power of glaciers.
Deformation of Quaternary strata and its relationship to crustal folds and faults, south-central Puget Lowland, Washington State
Derek Booth, University of Washington, Department of Earth and Space Sciences, Seattle, WA 98195, U.S.A., et al. Pages 505-508. Young, folded deposits in the south-central Puget Lowland of Washington State provide increased resolution of the character and rate of crustal deformation as a result of tectonic forces, forces that continue to produce earthquakes across this region today. Tectonic deformation has been ongoing for at least the past few hundred thousand years, and these folded deposits probably account for ~10% of the total shortening of the western Washington crust in recent time as a result of tectonic compression. The Seattle uplift, the prominent broad belt of uplifted sediments between downtown Seattle and Tacoma on which these folds are displayed, is clearly bounded by a major fault on its northern edge (the Seattle fault, last active 1100 years ago) and displays intense folding along its southern edge, lending support to prior and ongoing geophysical studies that suggest the likely location of an equivalent "Tacoma fault."
Sulfur, heat, and magma budget of Erta 'Ale lava lake, Ethiopia
Clive Oppenheimer, University of Cambridge, Department of Geography, Cambridge, England, UK, et al. Pages 509-512.
Erta 'Ale volcano, in the Danakil desert of Ethiopia, is one of the most remote volcanoes on Earth. It is important for its location on the rift separating Africa and Arabia, and for its long-lived eruption. For at least a century, one or more lava lakes have been active at the summit of the volcano. These pour heat and gases into the atmosphere but seldom overflow their craters to produce lava flows. We have measured for the first time both the heat and sulfur gas emissions from Erta 'Ale using field instruments. The results reveal how much magma must be continuously supplied to the lakes in order to maintain them, and cast light on the plumbing system of this unique volcano.
Natural bathymetric change as a control on century-scale shoreline behavior
Andrew Cooper and Fatima Navas, University of Ulster, Environmental Studies, Coleraine, Northern Ireland BT52 1SA, U.K. Pages 513-516.
At a time when attention is focused on climate change and sea level rise as major drivers of coastal erosion, Cooper and Navas attribute major changes in the shoreline to natural changes on the seafloor. A resort beach at Newcastle, Northern Ireland has been losing sand and suffering periodic erosion while an adjacent military zone has been seeing substantial sand buildup. Using modern data plus information from a 100-year-old chart, they studied wave dynamics under past and present conditions. The changing seabed caused significant changes in the wave field. This in turn led to changes in the sediment transport pathways. As a result, areas of substantial erosion and accretion have developed on the shoreline. When the resort was built, sand was being transported to its beaches by wave action. Now that situation has changed because of the changing seabed. Ironically, while the recreational beach is suffering erosion, the whole coastal system has an abundance of sand that, under present conditions, is being redistributed in a pattern incompatible with human uses. The paper points out that such changes must accompany sea level change on all coasts but that a lack of historic bathymetric data has likely inhibited such research elsewhere. The findings highlight the difficulty of isolating the effects of sea level rise from other causes of coastal erosion.
Enhanced marine productivity off western North America during warm climate intervals of the past 52 k.y.
Alexander van Geen, Columbia University, Lamont-Doherty Earth Observatory, Route 9W, Palisades, NY 10964-8000, U.S.A., et al. Pages. 521-524.
The valuable network of records showing rapid and contemporaneous changes in climate across the globe has been expanded with a new location off the southern tip of Baja California, Mexico. Such records provide an indication of the way climate has changed in the past and, therefore, hopefully also an indication of the way climate may change in the future. The 15-m-long sediment core, which spans the past 52 k.y. and was analyzed at up to 1 cm resolution, indicates a remarkably consistent teleconnection between changes in marine productivity at this eastern Pacific location with millennial-scale climate change over the North Atlantic, as recorded by the oxygen isotopic composition of Greenland ice. Previous studies of Santa Barbara Basin off California had linked related observations to changes in ventilation of the North Pacific rather than changes in productivity. One possible interpretation of the new data is that the deep nutricline and low productivity in the region associated with modern El Niño conditions was dominant during the cooler climate intervals of the past 52 k.y.
Reconstructing paleoelevation in eroded orogens
Andreas Mulch, University of Lausanne, Department of Mineralogy and Geochemistry, Lausanne, 1015, Switzerland, et al. Pages 525-528.
One of the factors controlling global climate change is global topography. Understanding paleotopographic variations is therefore important when reconstructing past climate histories. Topographic variations influence the isotopic composition of rain water and the elevation of a mountain range can be reconstructed from the isotope information contained in any precipitation reservoir, ideally a bucket of water collected at the mountain top. Evidence from a newly discovered precipitation reservoir, the stable isotope record of surface waters in zones of crustal deformation, indicates that elevations in the early Eocene North American cordillera were 1000 m higher than today and strongly influenced continental precipitation and climate patterns.
Records of post-K-T boundary millennial-scale cooling from the western Tethys: A smoking gun for the impact-winter hypothesis?
Simone Galeotti, Università degli Studi di Urbino, Istituto di Geologia, Campus Scientifico, Urbino, Italy 61029, Italy, et al. Pages 529-532.
The events that transpired on the day the dinosaurs died are much debated. Did direct effects of the Chixulub bolide cause the mass extinction at the K-T boundary, was it the subsequent global wildfires or acid rain or an "impact winter" caused by an enshrouding layer of impact-induced dust and aerosols? Galeotti et al. have found some of the first evidence of a long (>2 k.y.) cold period immediately post-impact, which they argue, on physical oceanographic grounds, is consistent with a long >3 year impact winter scenario. The study supports the hypothesis that the K-T boundary event was caused by an impactor and furthermore conjectures that changes in ocean stratification associated with the event may provide a mechanism to extend the post-impact adjustment of the deep ocean system to long time scales; this may be important for understanding why the post-K-T carbon cycle recovery time was so slow.
Changes in geyser eruption behavior and remotely triggered seismicity in Yellowstone National Park produced by the 2002 M7.9 Denali fault earthquake, Alaska
Stephan Husen, Swiss Federal Institute of Technology, Swiss Seismological Services, Zurich CH-8093, Switzerland, et al. Pages 537-540.
Following the large 2002 M7.9 Denali fault earthquake, Alaska, we observed clear changes in geyser activity and a series of local earthquake swarms in Yellowstone National Park, despite the large distance of 3100 km from the epicenter. Several geysers altered their eruption frequency within hours after the arrival of large amplitude seismic waves (Love and Rayleigh surface waves) from the Denali fault earthquake. In addition, earthquake swarms occurred close to major geyser basins such as Upper Geyser Basin. These earthquake swarms were unusual compared to past seismicity in that they occurred simultaneously at different geyser basins throughout the Yellowstone National Park region. We interpret these observations as being induced by dynamic stresses associated with the arrival of the large-amplitude seismic waves from the Denali fault earthquake. These dynamic stresses interact with fluids at major geyser basins, changing local permeability and pore pressures. Although changes in geyser activity and earthquake triggering have been documented previously, we present evidence for changes in a hydrothermal system induced by a large-magnitude event at a great distance, and for the important role hydrothermal systems play in remotely triggering seismicity.
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