How are sand dunes formed?
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Wind is the primary force that creates sand dunes. Sand itself is generally created by the erosion of rock material by water and ice.\n\nThere are two types of movement that wind causes in sand. One is called saltation. Wind picks up grains of sand and gives them forward momentum, but they will often fall back and bounce repeatedly, or cause other grains to move. This is about 75% of all movement of sand to form dunes. \n\nThe other movement method is called surface creep. Surface creep is the process where heavier sand grains are moved forward along a surface as saltating grains strike them.  It is estimated that about 25% of sand movement is moved this way. \n\nAs this moving sand encounters obstacles or changes in elevation such as a basin, the irregular flow of the wind will cause sand to accumulate in the "wind shadows." However, obstacles are not necessary to make dunes. The bouncing sand grains will gradually slow, losing energy from impacting heavier grains, and the sand itself tends to slow the wind speed close to the ground. Together, this differential speed of motion among grains, and saltation drag on the wind, will begin to produce small piles of sand, or ripples. Larger grains will tend to accumulate because the wind cannot move them, and cause more ripple effects.\n\nTrue dunes are formed when relatively strong winds blow over fine grained sands. The coarser grains tend to stabilize the windward surface of the dune, and finer grains are moved by saltation upward and over the peak of the dune, where they fall out of the wind and slip downward. \n\nIn areas of active dunes the dunes will migrate in the direction of the wind over periods of years. Many of the largest sand dunes in the world are considered paleodunes that are no longer moving. \n\nTo read more about sand dunes and how they form, as well as some information on the different types of sand dunes go here:\nhttp://www.nps.gov/whsa/Sand%20Dune%20Geology.htm
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The sand is wind blown, as it flows over the surface irregularities in the surface, or eddies in the wind slow it down in places and the sand is deposited ontoi the ground, this causes further flow disturbance and the sand pile expands upwards (in height).  The mini dune will have sloping sides, the side into the wind being longer and less steep than the leward side, and there is a limit for the steepness of the slope which is maintainable with dry sand(not sure what it is but look it up).  If the slope is greater than the limit, the sand will roll down hill spreading the dune along the ground (in the direction the wind is going).  This fills in the gap in front of the dune and raises the surface level, allowing more sand to build up on top, which then begins to move forward in a repeating cycle.
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There is only one basic source of sand for a beach, and that is from rivers. Secondarily, some beaches are created by ocean currents such as long-shore migration, where the sand is being moved along the shore to spots it may not have been before. \n\nAs far as river deposition, it will vary according to the sediment load of the river. The Mississippi River moves on average about 436,000 tons of sediment in a day. That one day's deposit of sediment probably has enough sand in it to create a fairly nice beach. Since the sand will most likely be deposited in a mouth bar or somewhere else on the delta, it may not be in the form of a beach, but that process is the source of almost all sand on beaches. Even beaches covered with volcanic sediments like in Hawaii still  most often depend on a river or stream to carry the sediment to the beach. In an extreme volcanic eruption a beach of volcanic ash might be deposited in a few hours. \n\nLong-shore drift creates many beaches, and is a relatively slow process. On some coastlines the wave action variation between winter and summer will make some sandy beaches disappear in winter and come back in summer, so in these cases it may only take a few months to create the beach.\n\nThe part of your question that you didn't ask: How long does it take to create the sand on a beach? That answer could be thousands to millions of years, as rock such as granite has to be weathered and eroded to create the sand grains that make up most sand.
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All waves go outward from their source, they don't all go straight to the beach, that's just the only place you can see them.  Waves originate from wind and other forces causing water particles to build up and roll over and on top of one another...they are usually not very noticable until they come closer to shore and the compression between the particles is sent upward.
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1. Yes and no.  Sand comes from rocks.  Metamophic rocks are shaped by extreme pressure which is responsible for some of the patterns you might see in rocks.  \n2. Yes.
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did you mean how do clouds form?\n\nIf so, they form from water evaporating on the surface of the earth. As the vapour rises, it reaches cooler, higher areas of the atmosphere and the vapour begins to condense, around microscopic particles in the air. Once this process has started, other molecules will start to join in, until the vapour condenses and clumps together. When enough forms, it is no longer lighter than air, and rain will occur.
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The valley is formed from rifting, so a streching of the crust creates an opening.  This also creates high mountains around the valley.  These mountain erode and this sand, gravel and mud is deposited into the new valley.  THey are transported mainly via streams and rivers, which all combine to form the Rio Grande River itself.
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To understand sedimentary rock layers, it is important to understand that the earth's surface is always slowly - but constantly - changing.  Mountains and other areas that are raised above the surrounding land are subject to wind, rain, and water which constantly wear them down.  The bits of sand, pebbles, and rubble that get worn down from mountains, mesas, and cliffs are pulled by gravity to the low-lying areas (valleys, lake beds, sea-shores) where they collect over time.  Over millions of years, these deposits can harden and petrify into sedimentary rock layers.  Other sedimentary rock layers (like limestone) form on ancient sea or lake beds and are the remains of the various animals and plants that lived in the water.\n\nThus when you look at the different layers of the Grand Canyon, you are looking at the petrified remains of what was once the surface of the earth (or the bottom of a sea bed) at a time the region was being covered with sedimentary material.  Different rock layers occur when changes to the environment cause one type of material to stop being deposited and new materials get deposited instead.  For example, a shallow sea may create layers of limestone.  If the sea later dries up and the now exposed sea bed gets covered over with blowing dry sand, then a layer of sandstone will be deposited on top of the limestone.  In this way, geologists can see how the surface of the earth changes at a given spot over time.\n\nAs for the specific rock layers in the Grand Canyon, here is a VERY SIMPLISTIC description of the situation and processes that produced the major rock layers (from the oldest layer at the bottom to newest at the top):\n\nVishnu Schist (bottom) - 1.7+ billion years ago the area around Grand Canyon was a series of volcanic islands surrounded by a shallow sea.  The resulting deposits of ash, sand, and mud created shales, sandstones and mudestones that were eventually compressed and distorted with time and pressure into gneiss and schist.\n\nTapeats Sandstone - There is a long period where the rocks from this area did not survive and so no record is left (the Great Unconformity).  Eventually this area became part of the edge of the still forming North American continent.  Sandy beaches in this area around 540 million years ago created this sandstone formation.\n\nBright Angel Shale - The water moved further inland, causing this area to be frequently underwater and covered with deposits of mud (which is where shale comes from).\n\nMuav Limestone - The water got deeper and the area became part of the sea-floor proper leading to limestone deposits.\n\nFollowing the Muav Limestone, the sea appears to have receded and the land was again above water.  Little is left from this period.\n\nRedwall Limestone - Around 363 million years ago, the sea moves in rapidly again and the area is once again part of a sea floor leading to limestone deposits.\n\nSupai Group and Hermit Shale - This is actually a lot of smaller layers (a mix of shales, mudstones, and limestones) created as the sea came in and went out numerous times over a period of 30 million years.\n\nCoconino Sandstone - The seas pulled back and this part of North America became part of a vast sand-dune filled desert (similar to North Africa).  The Coconino Sandstone is the petrified remains of ancient sand dunes.\n\nToroweap Formation and Kaibab Limestone (top of canyon) - The sea came back and turned the area first into shallow mud flats (Toroweap) and then drowned it completely into a sea floor (Kaibab) about 240 million years ago.\n\nOne frequent related question... how can Grand Canyon rock layers be from the bottom of a sea when the canyon rim is at 6000+ feet elevation, did the water get that high?  The answer is no... at the time that the sea floor deposits were created, this part of North America was much lower (ie: below sea level).  \n\nThe reason you can find limestone rock layers with fossil fish and clams at high elevations above current se
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Hi, Ishan,\n\nsee below some useful links. One is a news story about China's creeping deserts (BBC link); however, with climate change this is also seriously affecting E. Africa, where one can almost watch the dunes moving.
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There are three major ways that rocks are formed. The first of these is from heat ie- igneous rocks. They are the volcanic rocks, among which are obsidian, and granite. Both obsidian and granite contain the same minerals but their different appearances are caused by differences in the speed of their cooling. Obsidian cooled very rapidly and has a glassy texture.  Granite cooled very slowly and the separate minerals crystallized into larger crystal. The three major minerals of granite and obsidian are quartz, feldspar, and mica, each cool at a different rate.\n\n\nGranite is an Intrusive rock=\nIgneous rock that cools and solidifies beneath the Earth’s surface\n\nObsidian is an Extrusive rock=\nIgneous rock that cools and solidifies at or very near earths surface eg- in a lava flow
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A sand fire is a type of major storm that occurs in Vulcan deserts. These storms advance at high speeds and are characterized by strong winds and blinding sand. The effects of a sand fire on the desert also generates dangerous lightning-like discharges of electrical energy close to the ground. Sand fire storms can last from hours to days.
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it's like sand dunes with limited plant growth
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Deltas and Estuaries are created at the mouths of rivers.\nAnother landform that is created close to the mouth of a river is an ox bow lake.
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The wind blows sand and rubble. Erosion might also cause the land to shift.
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Iron and water.  Just wash the sand off the iron.
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I think you mean rock fragments. If yes,\n\nRock fragments are further eroded by forces of nature: wind or water. depending on the level of disintegration, it forms various kinds of soil or sand.\n\nSometimes if fragments get buried under several layers of soil, fragments clump together to form sedimentary rocks\n\nHope that helps\n\nR
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Wind is the movement of air in response to formation of low pressure cells.\n\nAs someone else stated earlier, the uneven heating of the earth is the primary source for the formation of wind.\n\nCertain parts of the world gets more sunlight than others. This creates uneven heating.\n\nAreas that accumulate more heat are associated w/ low pressure cells. Warm air is less dense than cooler air & will rise.\n\nLike everything else in nature, air pressure tends to want to balance out. That means high pressure will move toward low pressure. This is the beginning of wind.\n\nThe process above describes the global movement of wind that is associated w/ pressure belts around the globe. These are called global winds (ie trade winds, easterlies, etc.)\n\nLocal winds such as valley & mountain breezes as well as sea & land breezes are created in the same way except on a much smaller scale.\n\nLocal winds begin w/ uneven heating of earth's surfaces and/or waters.\n\nFor instance, w/ a sea breeze, localized low pressure will form over land during the day since land heats up faster & to much higher temps than water.\n\nAs the air rises, cooler denser air from over the ocean moves toward the land to replace the air that has risen. This creates a convection current in which the air will circulate, creating a constant breeze.\n\nHowever, at night, the opposite is true. Low pressure forms over the water. Since water cools off more slowly than land surfaces, the water will be the source of the low pressure & the reverse will take place.