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23-505: The Alum Cliffs are a section of cliffed coast facing the Derwent Estuary and Storm Bay along the suburbs of Taroona , Bonnet Hill , and Kingston Beach , Tasmania, Australia . Composed of Permian mudstone , the cliff formation stretches for 3.5 kilometres (2.2 mi) between Hinsby Beach and Tyndall Beach at Kingston Beach. The cliff face reaches heights of up to 30 metres (98 ft) above sea level and has vistas of

46-891: A cove . Weather-eroded arches begin their formation as deep cracks which penetrate into a sandstone layer. Erosion occurring within the cracks wears away exposed rock layers and enlarges the surface cracks isolating narrow sandstone walls which are called fins. Alternating frosts and thawing cause crumbling and flaking of the porous sandstone and eventually cut through some of the fins. The resulting holes become enlarged to arch proportions by rockfalls and weathering. The arches eventually collapse leaving only buttresses that in time will erode. Many weather-eroded arches are found in Arches National Park , Canyonlands National Park , and Grand Staircase–Escalante National Monument (GSENM), all located in southern Utah, United States. Some natural bridges may look like arches, but they form in

69-628: A stack is left behind on the wave-cut platform. The best-known example in Germany is the Lange Anna on Heligoland , while, in England, a prominent example are Old Harry Rocks in Dorset . Furthermore, on a rocky cliffed coast wave action is not the only driving force for coastline retreat. General weathering of the bedrock is almost equally important. "Living cliffs" are those on a coast that

92-747: A cave erosion arch made of limestone, is in Carter Caves State Resort Park and has a paved road on top. The second, a weather-eroded sandstone arch with a dirt road on top, is on the edge of Natural Bridge State Park in Kentucky. The latter arch is called White's Branch Arch (also known as the Narrows) and the road going over it is usually referred to as the Narrows Road. In Europe, the Romanian village of Ponoarele has

115-560: A span of 225 feet (69 m). The Rainbow Bridge National Monument 's namesake was also formed by flowing water which created the largest known natural bridge in the Western Hemisphere with a span of 234 feet (71 m), based on a laser measurement made in 2007. Xianren Bridge , also known as Fairy Bridge, in Guangxi , China is currently the world's largest known natural bridge with a span recorded at 400 feet (120 m) by

138-441: Is relatively resistant to erosion such as sandstone, limestone or granite, a flat rocky wave-cut platform or abrasion platform is formed in front of the cliff. It represents the foot of the cliff preserved at and below the level of water table. If there is a tectonic uplift of the coast, these abrasion platforms can be raised to form coastal terraces, from which the amount of uplift can be calculated from their elevation relative to

161-655: Is somewhat arbitrary. The Natural Arch and Bridge Society identifies a bridge as a subtype of arch that is primarily water-formed. By contrast, the Dictionary of Geological Terms defines a natural bridge as a "natural arch that spans a valley of erosion." The largest natural arch, by a significant margin, is the Xianren Bridge in China, with a span of 122 ± 5 meters (400 ± 15 ft). On coasts two different types of arches can form depending on

184-534: Is still active, i.e. that is being eroded and is receding. A "dead cliff", by contrast, is only reached by very high marine waves and is therefore subjected to very little change. A clear indication of a lack of activity at a dead cliff is a covering of vegetation that appears on the cliff as wave action against it subsides. Well-known coasts with living cliffs in Germany are the Red Cliff ( Rote Kliff ) in Kampen on

207-565: The Natural Arch and Bridge Society in October 2010, with a precision of ±15 feet (4.6 m). Natural bridges can form from natural limestone caves , where paired sinkholes collapse and a ridge of stone is left standing in between, with the cave passageway connecting from sinkhole to sinkhole. Like all rock formations, natural bridges are subject to continued erosion, and will eventually collapse and disappear. One example of this

230-542: The Derwent Estuary, Storm Bay, South Arm and Bruny Island . The first reference of the Alum Cliffs namesake was documented in 1847. The Alum Cliffs are made of Permian mudstone, containing pyrite . Once oxidised, the pyrite produces the chemical compound alum . The Alum Cliffs track is a popular 6 kilometres (3.7 mi) (2.5 hour) return walking track frequented by locals and tourists. A small track

253-430: The cliff-foot form a wave-cut notch by constant abrasion action producing an overhang. This overhang grows in size as the cliff is undercut, until it collapses under its own weight. The loose debris that has broken off is gradually carried away from the area in front of the cliff by the action of the sea. As the coastal cliffs collapse, the shoreline recedes inland. The speed at which this happens depends, in particular, on

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276-465: The coastline, with weak rock such as shale protected by stronger rock such as limestone . The wave action along concordant coastlines breaks through the strong rock and then erodes the weak rock very quickly. Good examples of this type of arch are the Durdle Door and Stair Hole near Lulworth Cove on Dorset 's Jurassic Coast in south England. When Stair Hole eventually collapses it will form

299-496: The formation beneath the relatively harder stratum, or caprock , above it. The alcoves erode further into the formation eventually meeting underneath the harder caprock layer, thus creating an arch. The erosional processes exploit weaknesses in the softer rock layers making cracks larger and removing material more quickly than the caprock; however, the caprock itself continues to erode after an arch has formed, which will ultimately lead to collapse. The choice between bridge and arch

322-573: The geology. On discordant coastlines rock types run at 90° to the coast. Wave refraction concentrates the wave energy on the headland, and an arch forms when caves break through the headland. Two examples of this type of arch are London Bridge in Victoria , Australia, and Neill Island in the Andaman Islands , India. When these arches eventually collapse, they form stacks and stumps. On concordant coastlines rock types run parallel to

345-648: The island of Sylt or the chalk cliffs on the Jasmund Peninsula. The Königsstuhl on the island of Rügen is a good example of a dead cliff. Others may be found in the regions of the present-day Wadden Sea coast of the North Sea a few kilometres inland. These show the former coastline from which the sea retreated as the level of water in the North Sea fell. Steep sea cliffs can also be caused by catastrophic debris avalanches . These have been common on

368-444: The land surface dips at a relatively steep angle below the water table, the continuous action of marine waves on the coastline, known as abrasion , may create a steep declivity known as a cliff , the slope angle of which depends on a variety of factors including the jointing, bedding and hardness of the materials making up the cliff as well as the erosional processes themselves. The slope is constantly being eroded. The waves attacking

391-458: The path of streams that wear away and penetrate the rock. Pothole arches form by chemical weathering as water collects in natural depressions and eventually cuts through to the layer below. Natural Bridges National Monument in Utah protects the area surrounding three large natural bridges, all of which were formed by streams running through canyons, the largest of which is named Sipapu Bridge with

414-434: The red sandstone cliffs on Heligoland . There are, however, differences between the former and the latter regarding some peculiarities of the coast line. In the case of the large and widespread coastal cliffs of Atacama Desert the modern cliffs originated from a process of scarp retreat of a fault scarp , thus at present the cliffs do not follow any geological fault . On a rocky cliffed coast made up of material which

437-425: The sea level, taking into account any eustatic sea level changes . On a cliffed coast made up of material which is only fairly or even hardly resistant to erosion no wave-cut platform but a beach is formed in front of the sea cliff. If waves carve notches at a narrow point on both sides of a promontory on the rocky cliffed coast, a natural arch may be formed. When the arch collapses as the coastline recedes further

460-663: The strength of the surf, the height of the cliff, the frequency of storm surges and the hardness of the bedrock . Thus, the Mecklenburg coast in Germany recedes by about 25 centimetres per year, whereas the chalk cliffs of southern England retreat by just half a centimetre each year. A cliffed coast is made of a loose bedrock material, such as at the Red Cliff on the German island of Sylt , but can also occur in hard rock like

483-905: The submerged flanks of ocean island volcanos such as the Hawaiian Islands and the Cape Verde Islands . Natural arch A natural arch , natural bridge , or (less commonly) rock arch is a natural landform 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). Most natural arches are formed from narrow fins and sea stacks composed of sandstone or limestone with steep, often vertical, cliff faces. The formations become narrower due to erosion over geologic time scales . The softer rock stratum erodes away creating rock shelters , or alcoves, on opposite sides of

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506-526: Was initially developed in the 1970s and formally developed as part of Australia's Bicentennial celebrations in 1988. In 2018, a council proposal was put forward to upgrade the track to facilitate mountain biking. The Alum Cliffs track is accessible via Tyndall Beach at Kingston Beach and the Channel Highway . This Tasmania geography article is a stub . You can help Misplaced Pages by expanding it . Cliffed coast In coastal areas in which

529-642: Was the double-arched Victorian coastal rock formation, London Bridge , which lost an arch after storms increased erosion. Moon Hill in Yangshuo , Guizhou Province , China, is an example of an arch formed by the remnant of a karst limestone cave. In a few places in the world, natural arches are utilized by humans as transportation bridges with highways or railroads running across them. In Virginia, US Route 11 traverses Natural Bridge . Two additional natural arch roadways are found in Kentucky . The first,

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