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Hello guys - i want create Sand Dunes like in this Picture: I startet to create a simple Perlinnoise in a Point-Vop to Displacement geometry...

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Sand dunes are hills of sand that are deposited by the wind. Wind transports sand across the sand dunes that causes abrasion, it's when sand scrapes against rocks and creates damage. Wind can tear down land forms and erode sediments.

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That's the question for two Utah Boy Scout leaders who decided that a hoodoo-that's the name for a rock formation that looks like a column with a mushroom cap-needed to lose its top.

It seemed to them as if the cap were precariously balanced and could fall and hurt someone. So the guys toppled it. And made a video of their feat and posted it to YouTube. After being booted as Boy Scout leaders on Tuesday, the pair could face criminal charges for the incident at Goblin Valley State Park.

For insights into these rock formations-and whether they're indeed precarious-we turned to Marjorie Chan , a professor in the department of geology and geophysics at the University of Utah.
So what is a hoodoo?
A spire of rock that has an easily eroded column and a more resistant cap. Sometimes they look like mushrooms. They are kind of eerie, so they're called "hoodoos" and also have other names, from "fairy chimneys" to "goblins."
And what creates these freestanding columns?
It's a function of weathering and erosion in desert climates. Water from streams, runoff, and intense thunderstorms wear down the rock, especially along joints and cracks in the formation. Wind is the fine sculptor that does a lot of the smoothing and finishing.

There are two different things when we talk about the age of these features. Number one is the basic rock: When was it deposited? About 170 million years ago, a tongue of the ocean came down from the north; sand and mud were deposited near an ancient shoreline. They were buried and turned into the Entrada Sandstone formation. So that's the age of the unit itself-when it was laid down.

But the formation of the hoodoos, these erosional remnants, is much younger. That age is not really clear and is very difficult to date. They're the result of a gradual process of erosion that began about 25 million years ago.

Hoodoos occur in many places, but Goblin Valley has a high concentration in a small area. To me, Goblin Valley is a magical place. It's a place I took my kids when they were young, one of the very few places where kids can crawl all over the rocks and play hide and seek, because these goblins are [scaled in a way] that kids love and can explore. I would be sad if, because of what happened, the parks don't allow as much free access.

Wind and weather does. There are clays [in the rocks] that shrink and swell. If we have a big thunderstorm, a flash flood, there's more water erosion. The rocks are constantly modified by the elements because the environment is dynamic.

People have been walking around the goblins for years. One of the things we don't know is the effect of foot traffic and people climbing on goblins.

I believe we need to do a better job of inventorying these goblins, to do a census and measurements, to evaluate how they change over time.

Some of them are precariously balanced. You have the softer rock underneath the more resistant sandstone cap, and [the softer rock] does tend to weather away. It's surprising that an accident hasn't happened before.

We don't know. It could have toppled over, but it could have lasted another hundred years or more.

The proper thing to do, if you see something that looks precarious, is to report it. Let the people in charge make the decisions about what to do.

The backlash he's experienced shows that people feel strongly about these extraordinary rock formations that are part of the park. And they feel that the rocks belong to everyone.

We need to be good stewards of this magical landscape. We should preserve it and enjoy it.

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After Utah Video Scandal, a Primer on Hoodoos

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That's the question for two Utah Boy Scout leaders who decided that a hoodoo-that's the name for a rock formation that looks like a column with a mushroom cap-needed to lose its top. It seemed to them as if the cap were precariously balanced and could fall and hurt someone.

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Frost wedging is the main process that forms the hoodoos. As water from snow melts, it creeps up into the cracks of the rocks, then as it freezes it expands and cracks the rocks. After multiple processes the rocks form a hoodoo. Dissolution also occurs because of the acidic rainwater breaks down limestone.

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The Pinnacles, Nambung National Park, Western Australia - Tourism Australia

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Discover a true desert landscape in Nambung National Park, where the weathered rock spires of the Pinnacles rise out of yellow sand dunes. Learn more.

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A natural arch, natural bridge, or (less commonly) rock arch is a natural rock formation where an arch has formed with an opening underneath. Natural arches commonly form where inland cliffs, coastal cliffs, fins or stacks are subject to erosion from the sea, rivers or weathering ( subaerial processes).

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Dissolution happened in cold wet winters when rain dissolved the limestone rocks that hap been placed down. Wind came into place and blew most of the vegetation away leaving only rocks, looking like spiky rocks.

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Archs are formed when big cliffs are surrounded by a river or ocean and the saltwater dissolves the limestone rocks and creates a window looking like an arch. Also if the cliff is located near where a sink hole is and the ground just sinks then it can also create an arch.

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A talus slope is formed mainly by frost wedging and dissolution. As water creeks into the small cracks in the large rocks, and as it freezes it wedges rocks and breaks them apart causing them to fall down the cliff and bundle up at the bottom of the cliff. Some dissolution occurs if there's ever any rain.

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V-shaped valleys are formed when rivers flow through a valley, and carry large boulders causing vertical erosion. At the same time the hillsides above get broken down by dissolution from the rain. Then because of gravity rock slides shove rocks down towards the river.

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Meandering stream dictionary definition | meandering stream defined

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meandering stream definition: nounA stream that has multiple successive meanders and develops in relatively flat areas, such as a floodplain, where sediment consists primarily of fine sands, silts, and muds. meandering stream ...

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A meandering stream forms when a river erodes the sides and widens the valley. And when it erodes it on the side it deposits a silt making the stream zigzag.

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This picture of the Nowitna River in Alaska shows two oxbow lakes - a short one at the bottom of the picture and a longer, more curved one at the middle-right. The picture also shows that a third oxbow lake is probably in the making: the isthmus or bank in the centre of the most prominent meander is very narrow - much narrower than the width of the river; eventually, the two sections of river on either side of an isthmus like that tend to break through and create a new, straighter course; a new river bank then starts to accumulate, sealing off the meander and leaving another oxbow lake.

An oxbow lake is a U-shaped lake or pool that forms when a wide meander of a river is cut off, creating a free-standing body of water. The word "oxbow" can also refer to a U-shaped bend in a river or stream, whether or not it is cut off from the main stream.

In South Texas, oxbows left by the Rio Grande are called . In Australia, oxbow lakes are called billabongs.

A meander develops into an oxbow lake

An oxbow lake forms when a meandering river erodes through the neck of one of its meanders. This takes place because meanders tend to grow and become more curved over time. The river then follows a shorter course that bypasses the meander. The entrances to the abandoned meander eventually silt up, forming an oxbow lake. Because oxbow lakes are stillwater lakes, with no current flowing through them, the entire lake gradually silts up, becoming a bog or swamp and then evaporating completely. When a river reaches a low-lying plain, often in its final course to the sea or a lake, it meanders widely. In the vicinity of a river bend, deposition occurs on the convex bank (the bank with the smaller radius). In contrast, both lateral erosion and undercutting occur on the cut bank or concave bank (the bank with the greater radius). Continuous deposition on the convex bank and erosion of the concave bank of a meandering river cause the formation of a very pronounced meander with two concave banks getting closer. The narrow neck of land between the two neighboring concave banks is finally cut through, either by lateral erosion of the two concave banks or by the strong currents of a flood. When this happens a new, straighter river channel develops-and an abandoned meander loop, called a cutoff, forms. When deposition finally seals off the cutoff from the river channel, an oxbow lake forms. This process can occur over a time from a few years to several decades, and may sometimes become essentially static.

Gathering of erosion products near the concave bank and transporting them to the convex bank is the work of the secondary flow across the floor of the river in the vicinity of a river bend. The process of deposition of silt, sand and gravel on the convex bank is clearly illustrated in point bars.

The effect of the secondary flow can be demonstrated using a circular bowl. Partly fill the bowl with water and sprinkle dense particles such as sand or rice into the bowl. Set the water into circular motion with one hand or a spoon. The dense particles quickly sweep into a neat pile in the center of the bowl. This is the mechanism that leads to the formation of point bars and contributes to the formation of oxbow lakes. The primary flow of water in the bowl is circular and the streamlines are concentric with the side of the bowl. However, the secondary flow of the boundary layer across the floor of the bowl is inward toward the center. The primary flow might be expected to fling the dense particles to the perimeter of the bowl, but instead the secondary flow sweeps the particles toward the center.

The curved path of a river around a bend makes the water's surface slightly higher on the outside of the bend than on the inside. As a result, at any elevation within the river, water pressure is slightly greater near the outside of the bend than on the inside. A pressure gradient toward the convex bank provides the centripetal force necessary for each parcel of water to follow its curved path.

The boundary layer that flows along the river floor does not move fast enough to balance the pressure gradient laterally across the river. It responds to this pressure gradient, and its velocity is partly downstream and partly across the river toward the convex bank. As it flows along the floor of the river, it sweeps loose material toward the convex bank. This flow of the boundary layer is significantly different from the speed and direction of the primary flow of the river, and is part of the river's secondary flow.

A Horseshoe or oxbow lake near Hughes, Arkansas. The bulges in the border reflect changes in the course of the river; when the river shifted its course and cut off the former channel, the border remained unchanged.

River flood plains that contain rivers with a highly sinuous platform are populated by longer oxbow lakes than those with low sinuosity. This is because rivers with high sinuosity have larger meanders, and greater opportunity for longer lakes to form. Rivers with lower sinuosity are characterized by fewer cutoffs and shorter oxbow lakes due to the shorter distance of their meanders.

Oxbow lakes on New Zealand's Taieri River have been converted into water meadows.

Oxbow lakes form favorable habitats for wildlife communities. These often have unique characteristics. For example, the numerous oxbow lakes of the Amazon River are a favorable habitat for the giant river otter. Oxbow lakes may also be suitable locations for aquaculture.

Oxbow lakes contribute to the health of a river ecosystem by trapping sediments and agricultural runoff, thereby removing them from the main river flow. However, this is destructive of the oxbow lake ecosystem itself. Oxbow lakes are also vulnerable to heavy metal contamination from industrial sources.

Oxbow lakes may be formed when a river channel is straightened artificially to improve navigation or for flood alleviation. This occurred notably on the upper Rhine in Germany in the nineteenth century.

An example of an entirely artificial waterway with oxbows is the Oxford Canal in England. When originally constructed, it had a very meandering course, following the contours of the land, but the northern part of the canal was straightened out between 1829 and 1834, reducing its length from approximately 146 to 125 km (91 to mi) and creating a number of oxbow-shaped sections isolated from the new course.

Bole and Burton Round in West Burton, Nottinghamshire, England are a good example of previous lakes in a close proximity to one another.

Carter Lake, Iowa was created after severe flooding in 1877 led to the Missouri River shifting approximately two kilometres ( miles) to the southeast.

Cuckmere Haven in Sussex, England contains a widely meandering river with many oxbow lakes, often referred to in physical geography textbooks.

Halfmoon Lake in downtown Eau Claire, Wisconsin was formed due to a shift in the course of the Chippewa River, which now flows immediately to the south.

Kanwar Lake Bird Sanctuary, India contains rare and endangered migratory birds and is one of Asia's largest oxbow lakes.

The Oxbow, a four-kilometre (-mile) bend in the Connecticut River, is disconnected at one end.

There are many oxbow lakes alongside the Mississippi River and its tributaries. The largest oxbow lake in North America, Lake Chicot (located near Lake Village, Arkansas), was originally part of the Mississippi River, as was Horseshoe Lake, the namesake for the town of Horseshoe Lake, Arkansas. Reelfoot Lake in west Tennessee is another notable oxbow lake; it was formed when the Mississippi River took a new channel following the 1811-12 New Madrid earthquakes.

The upper reaches of New Zealand's Taieri River has also cut a multitude of oxbow lakes in its upper course near the town of Paerau. Some of this area has been converted into water meadows.

Vynthala Lake, Chalakudy, India is formed from a "cutoff" of the Chalakudy River which flows nearby.

There has also been a possible oxbow lake postulated in Saraswati Flumen near Ontario Lacus on Saturn's moon Titan.

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An oxbow lake is a U-shaped lake or pool that forms when a wide meander of a river is cut off, creating a free-standing body of water. The word "oxbow" can also refer to a U-shaped bend in a river or stream, whether or not it is cut off from the main stream.

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Sinkholes are cavities in the ground that form when water erodes an underlying rock layer.

Two types of sinkholes exist. One forms when the roof of a cave collapses and exposes the underground cavern. The second type forms when water dissolves the rock underneath soil and creates an underground chasm. Without rock to support it, the soil layer collapses and creates a hole on the surface.

Sinkholes have both natural and human causes. Land made of a soft underground rock layer, such as rock salt around the Dead Sea or limestone in Mexico's Yucatan Peninsula, are often riddled with sinkholes, since the rock layer is easily dissolved.

Manmade sinkholes are created when city development compromises the structural integrity of underlying rock. Roads, buildings, and other types of construction may cause water to collect in certain areas and wash away the supporting rock layer (especially at low sea levels and after a heavy rainfall).

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Find Out What's Creating These Mysterious Holes

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Sinkholes are cavities in the ground that form when water erodes an underlying rock layer. Two types of sinkholes exist. One forms when the roof of a cave collapses and exposes the underground cavern. The second type forms when water dissolves the rock underneath soil and creates an underground chasm.

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Hydrolysis destroys the outside of the bank of the stream as well as abrasion and erosion. After a long period of time the river starts to pave away, then as a flood occurs it fills the river.

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As bedrock and water combine the ground breaks down all the limestone and collapses the cave roof. Also as moisture saturated the ground and cracks it, the ground could fall into another cave causing it to collapse.

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We are pleased to announce that Luray Caverns is now step-free! The steps that lead tours from the Entrance Lobby into the caverns are now bypassed by a looping covered walkway and a 164-foot corridor that was excavated into the hillside adjacent to the Entrance Building.

We are now one of the few underground marvels providing both a step-free entrance and tours on all-paved walkways, making us more accessible to visitors today and into the future.

Down below,
your imagination will soar.

Luray Caverns is the largest caverns in the eastern United States, yet walking through feels more akin to an unearthly experience.

Visit Geology's Hall of Fame. Guided tours along lighted, paved walkways lead visitors through cathedral-sized rooms with ceilings 10-stories high, towering stone formations, and natural wonders at every turn. Questions? See our FAQs.

Discover Luray Caverns

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Discover Luray Caverns in Virginia's Shenandoah Valley

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We are pleased to announce that Luray Caverns is now step-free! The steps that lead tours from the Entrance Lobby into the caverns are now bypassed by a looping covered walkway and a 164-foot corridor that was excavated into the hillside adjacent to the Entrance Building.

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Water creeps down far into the ground paving a way, then once it reached bedrock/limestone it slowly starts to dissolve the rock along the joints and fractures.

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An arête is a narrow ridge of rock which separates two valleys. It is typically formed when two glaciers erode parallel U-shaped valleys. Arêtes can also form when two glacial cirques erode headwards towards one another, although frequently this results in a saddle-shaped pass, called a col.

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An arete is created when two glaciers side by side erode a two different sides of a mountain to make one mountain that looks like a pointy hill. More specifically a glacier on the side of a mountain plucks the rocks out of the ground and moves down the mountain causing abrasion.

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Slump and rock slide on Rt. 52 near Ellenville NY | NESTA

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Slump and rockslide closing Rt. 52 near Ellenville, NY, Jan 2003. Original image taken by Jean McMahon and NYS DOT.

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Slumps can occur by natural disasters like an earthquake, in an instant, or it could take a long time and break apart the ground below into many different sections. It could happen through frost wedging, or dissolution.