Grain stream
A grain flow ( Engl . Grain Flow ) is a mass transport process such. B. a sand slide on the leeward side of a dune .
Origin and special features
At the beginning of the process only gravitational forces act at first , which is why z. B. in the formation of dunes a slope of about 30 degrees is necessary to cause the sediment grains to flow. When the particles are in motion, grain collisions occur, which loosen up the sediment and exert additional pressure on the grains contained. Due to the higher grain density in the lower area, there is a higher shear force that drives the larger particles into the upper areas. These particles then act as a kind of sieve that only lets small grains through into the deeper areas of the grain flow. These mechanisms result in an inverse gradation within a grain flow, with the coarser particles at the top and the finer ones at the bottom.
Classification
A distinction is made between unchanged and changed grain flows. While unchanged grain flows are only a few centimeters thick, changed grain flows can form thick sediments due to proportions of clay and rubble . Since clay acts as a kind of lubricant in this process , altered grain flows can already form on flatter slopes.
swell
literature
- Hans Füchtbauer (1988): 13. Transport processes and sediment structures. - In: Hans Füchtbauer [Ed.], Sediment-Petrology, Part 2, Sediments and sedimentary rocks. - 4th edition: 779–863, 61 figs., 9 tab .; Stuttgart (Swiss beard).
- Hans-Erich Reineck (1984): Actuogeology of clastic sediments. - Senckenberg-Buch , Vol. 61: 348 p., 250 fig., 12 tab .; Frankfurt am Main (Kramer).
- Andreas Schäfer (2005): Clastic Sediments. Facies and sequence stratigraphy. - X + 414 p., 342 ill .; Munich (Elsevier).