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Revolving Rivers
Revolving rivers are a surprising, uncommon way of sand pile growth that can be found in a few sands around the world, but has been studied in detail only for one Cuban sand from a place called Santa Teresa ( Pinar del Rio province). Description When pouring "revolving" sand on a flat surface from a fixed position, the growth of a conical pile does not occur by the common avalanche mechanism, where sand slides down the pile in a more or less random fashion. What happens in that a relatively thin "river" of flowing sand travels from the pouring point at the apex of the pile to its base, while the rest of the sand at the surface is static. In addition, the river "revolves" around the pile either in clockwise or counter-clockwise directions (looking from top) depending on the initial conditions. Actually the river constitutes the "cutting edge" of a layer of sand that deposits as a helix on the conical pile, and makes it grow. For small sandpiles, rivers are continuous, but they become ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Sand
Sand is a granular material composed of finely divided mineral particles. Sand has various compositions but is usually defined by its grain size. Sand grains are smaller than gravel and coarser than silt. Sand can also refer to a textural class of soil or soil type; i.e., a soil containing more than 85 percent sand-sized particles by mass. The composition of sand varies, depending on the local rock sources and conditions, but the most common constituent of sand in inland continental settings and non-tropical coastal settings is silica (silicon dioxide, or SiO2), usually in the form of quartz. Calcium carbonate is the second most common type of sand. One such example of this is aragonite, which has been created over the past 500million years by various forms of life, such as coral and shellfish. It is the primary form of sand apparent in areas where reefs have dominated the ecosystem for millions of years, as in the Caribbean. Somewhat more rarely, sand may be composed ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
