According to the terminology of geography and geology, a vertical or nearly vertical exposure of a surface of a rock or a hill or a mountain is known as a Cliff. They are generally formed because of the erosion of landforms by the weathering forces of nature. For example, a cliff near the water body such as a sea or an ocean is caused by the erosion of the rocks by the water waves over a period of years. Aside from the sea-shores or coasts, a cliff edge is most commonly found in mountainous areas, escarpments, and along the rivers. If a rock is resistant to weathering and erosion, it generally results in the emergence of a cliff.
Formation of a Cliff
The formation of a cliff happens mostly with sedimentary rocks. Sedimentary rocks such as sandstone, limestone, chalk, and dolomite are most likely to form a cliff. Sometimes, if there is a landslide formed because of a geologic activity then it can also lead to the emergence of a cliff edge. In old mountains, a mountain cliff can appear because of landslides caused due to the differential erosion of rock layers of differing hardness.
In arid areas, a cliff edge can be determined by the jumbles of fallen rock. It means that in such areas, a rock that has fallen because of erosion, can give rise to the emergence of a cliff side. Opposite to that in areas of high moisture, a soil slope alongside an elevated portion of the earth can give rise to a cliff side. Certain mountain cliffs are part of the tributary waterfalls or rock shelters as well. Sometimes the edge of a cliff is created at the end of a ridge with different types of rock columns such as mushroom rocks. And as already stated before, coastal erosion by the waves can lead to the creation of the edge of a cliff which is the sea-cliffs on the receding coastline.
The Ordnance Survey - a national mapping agency of Great Britain differentiates between cliffs and outcrops. According to them, a vertical exposure can be called a cliff only when it forms a continuous line along the top edge of the exposure (top edge of a cliff) with downward projections towards the land surface. They call the continuous lines along the lower edges as outcrops.
Large and Famous Cliffs
As per the above definition of a cliff, there is confusion in the extent of vertical exposure that is to be considered. There are various questions such as how much of the vertical slope be counted as a cliff. One can totally consider the combination of a vertical rock wall with a very steep slope as the cliff in terms of vertical exposure or only consider the rock wall as the cliff. Setting apart these doubts, one can find ascertaining qualities in some of the cliffs that are found around the world.
Some of the largest cliffs on Earth are actually found underwater. A glistening example of such a cliffy feature is the ridge found sitting inside the Kermadec Trench. It has an 8000 m drop with a 4250 m width.
Another example of the highest cliffs is the steep non-vertical cliffs of Nanga Parbat: The Rupal Face and Gyala Peri. Both of them rise approximately 4600 meters or 15000 feet high above their base.
The east face of the Great Tango in the Karakoram range of mountains of northern Pakistan is said to be one of the highest cliffs with a height of 1340 meters steep face. This height of this mountain cliff is considered by referring to the nearly vertical headwall of two stacked pillars which adds a very steep approach bringing the total drop from this cliff top of the east face to the nearby Dunge Glacier making it to 2000 meters.
One of the highest sea-cliffs stated by the Guinness World Records is Kalupapa in Hawaii. The height of this cliff from the cliff top is measured to be 1010 meters. The north face of Mitre Peak in New Zealand is also one of the competitors for the title of the world’s highest sea-cliff in the world. The north face of the Mitre peak has a height of 1683 meters. But these cliffs are taken into consideration by referring to the less stringent definition of the cliff as they also include it even though they have average slopes of 1.7 corresponding to 60° angle. A more stringent view of the definition is accepted for the vertical cliff found at Maujit Qaqarssuasia situated in the Torssukátak fjord area located at the tip of South Greenland having a vertical height of 1560 meters.
Mount Thor on Baffin Island in Arctic Canada is often referred to as the highest cliff with a height of 1370 meters. This height is inclusive of the cliff hanging part which does not form part of the 1250 meter which is said to be the longest vertical drop on Earth. But there is a possibility that the Polar Sun Spire in Sam Ford Fjord, in the Baffin Island may be higher than this.
One interesting fact is that the highest cliff in the Solar System is said to be Verona Rupes which is approximately 20 kilometers of height found on the fault scarp on Miranda, a moon of Uranus.
Life Forms and Folklore
Clifftops and surrounding areas provide a unique ecosystem that is part of diverse habitat niches of a variety of plants and animals. An interesting fact is that many birds have decided preferences for choosing cliff locations for nesting and are often chosen because of their defensibility and absence of certain predators.
The word ‘cliffhanger’ or cliff hanging became popular because the character in the novel To Kill a Mockingbird is hanging on the edge of a cliff. Thus, apart from being a source of scenic beauty cliffs form an integral part of the ecosystem and habitats with cultural values as well.