|
In geography and geology, a cliff is a vertical, or near vertical, rock exposure. Cliffs are formed as erosion landforms due to the processes of erosion and weathering that produce them. Cliffs are common on coasts, in mountainous areas, escarpments and along rivers. Cliffs are usually formed by rock that is resistant to erosion and weathering. Sedimentary rocks most likely to form cliffs include sandstone, limestone, chalk, and dolomite. Igneous rocks such as granite and basalt also often form cliffs. An escarpment (or scarp) is a type of cliff, formed by the movement of a geologic fault, or a landslide. Most cliffs have some form of scree slope at their base. In arid areas or under high cliffs, these are generally exposed jumbles of fallen rock. In areas of higher moisture, a soil slope may obscure the talus. Many cliffs also feature tributary waterfalls or rock shelters. Sometimes a cliff peters out at the end of a ridge, with tea tables or other types of rock columns remaining. Coastal erosion may lead to the formation of sea cliffs along a receding coastline. The Ordnance Survey distinguishes between cliffs (continuous line along the top edge with projections down the face) and outcrops (continuous lines along lower edge). ==Large and famous cliffs== Given that a cliff need not be exactly vertical, there can be ambiguity about whether a given slope is a cliff or not, and also about how much of a certain slope to count as a cliff. For example, given a truly vertical rock wall above a very steep slope, one could count just the rock wall, or the combination. This makes listings of cliffs an inherently uncertain endeavor. Some of the largest cliffs on Earth are found underwater. For example, an 8,000-metre drop over a 4,250-metre span can be found at a ridge sitting inside the Kermadec Trench. The highest cliff (rock wall, mountain face) in the world, is Nanga Parbat's Rupal Face, which rises approximately 4,600 metres, or 15,000 feet, above its base. According to other sources, the highest cliff in the world, about 1,340 m high, is the east face of Great Trango in the Karakoram mountains of northern Pakistan. This uses a fairly stringent notion of cliff, as the 1,340 m figure refers to a nearly vertical headwall of two stacked pillars; adding in a very steep approach brings the total drop from the East Face precipice to the nearby Dunge Glacier to nearly 2,000 m. The location of the world's highest sea cliffs depends also on the definition of 'cliff' that is used. ''Guinness World Records'' states it is Kalaupapa, Hawaii, at 1,010 m high. Another contender is the north face of Mitre Peak, which drops 1683 metres to Milford Sound, New Zealand. These are subject to a less stringent definition, as the average slope of these cliffs at Kaulapapa is about 1.7, corresponding to an angle of 60 degrees, and Mitre Peak is similar. A more vertical drop into the sea can be found at Maujit Qaqarssuasia (also known as the 'Thumbnail') which is situated in the Torssukátak fjord area at the very tip of South Greenland and drops 1,560 m near-vertically.〔(【引用サイトリンク】url=http://www.planetfear.co.uk/articles/Greenland_New_Route_on_Thumbnail_926.html )〕 Considering a truly vertical drop, Mount Thor on Baffin Island in Arctic Canada is often considered the highest at 1370 m (4500 ft) high in total (the top 480 m (1600 ft) is overhanging), and is said to give it the longest vertical drop on Earth at 1,250 m (4,100 ft). However, cliffs on Baffin Island, such as Polar Sun Spire, or others in remote areas of Greenland may be higher. The highest cliff in the solar system may be Verona Rupes, an approximately high fault scarp on Miranda, a moon of Uranus. The following is an incomplete list of cliffs of the world. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「cliff」の詳細全文を読む スポンサード リンク
|