|Dune complex of China's Badain Jaran Desert. Source|
martes, 25 de noviembre de 2014
Formation of the highest sand dunes on Earth
In physical geography, a dune is a hill of sand built by either wind or water flow. Dunes occur in different shapes and sizes, formed by interaction with the flow of air or water. Although the most widely distributed dunes are those associated with coastal regions, the largest complexes of dunes are found inland in dry regions and associated with ancient lake or sea beds.
How highest sand dunes on Earth are formed?
To explain how Earth's tallest dunes formed, scientists previously focused on wind conditions and sand characteristics. Recent research by Yang et al. (2011) suggested that a more complicated process is at work. By combining Landsat images that show variation in dune morphology (shape and size) with gravity measurements of the hilly bedrock below, Yang and colleagues showed that dune height is significantly influenced by local geology.
Yang et al. (2011). Formation of the highest sand dunes on Earth. Geomorphology, 135: 108-116
Characterization of dune morphology has historically been based on relationships between dune forms and wind regimes with dune height shown to be sensitive to atmospheric boundary layer depth, sand availability and sediment properties. While these parameters have been used in numerical simulations to model the occurrences of some types of dunes, they cannot alone explain the great diversity in form and size seen on Earth and on other solar system bodies. Here we present results from our studies of dune formation in the Badain Jaran Desert in western China, where Earth's tallest dunes occur. We measured the variability of the dune morphology in this desert on the basis of LANDSAT ETM+ data, and we detected the bedrock landforms beneath the aeolian sands by applying gravity methods. Wind records from stations at the periphery of the desert and SRTM topographical data were examined also to augment the interpretation. Our studies demonstrate that in addition to average wind parameters, dune height is highly sensitive to local geology, subsurface characteristics, and topography, and interactions between changing climate conditions and aeolian and fluvial processes. These additional factors need to be considered in the interpretation and simulation of dunes on Earth. We anticipate that analysis of anomalous dune heights like those seen in the Badain Jaran may also provide critical information on subsurface characteristics and environmental conditions on Earth and on other planetary bodies.
Miquel Mir Gual