of residual melt that was enriched in fast-diffusing H2O, but not yet evolved in slower-diffusing major elements, allowing Schipper and colleagues to put time scales on the onset of melt segregation within the framework that these subaqueous pyroclasts are among the fastest-quenched natural volcanic rocks known. Their results shed light on the earliest stages of melt segregation that are normally overprinted in slower cooling magmas and indicate that segregation begins over time scales of seconds rather than the days to centuries required of phenemonologically similar processes in lava flows or magma chambers.
Origin and evolution of interdistributary delta plains; insights from Mekong River delta
Toru Tamura et al., Geological Survey of Japan, AIST (National Institute of Advanced Industrial Science and Technology), Central 7, 1-1-1 Higashi, Tsukub, Ibaraki 305-8567, Japan; and Sheffield Centre for International Drylands Research, University of Sheffield, Winter Street, Sheffield S10 2TN, UK. Published online 28 Feb. 2012; doi: 10.1130/G32717.1.
River deltas have a range of geometry resulting from the interplay of coastal processes, river discharge, and sediment supply. Almost 25% of the world's population lives on deltaic lowlands, so prediction of delta growth is critical. However, knowledge of processes responsible for delta geometries is not well established, even though such knowledge is critical for risk management of land use and settlements on deltas. The Mekong River delta of southern Vietnam is one of the largest deltas in the world and offers a unique opportunity for understanding the sedimentary evolution of a river delta that is formed by a combination of tidal and wave processes. Toru Tamura of the Geological Survey of Japan and colleagues constrained the three-dimensional sedimentary evolution of the delta plains by determining ages of landforms that record past shoreline position and subsurface delta sedimePage: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 Related biology news :1
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