Mount Roraima

Mount Roraima (Spanish: Monte Roraima; Tepuy Roraima; Cerro Roraima; Portuguese: Monte Roraima) is the highest of the Pacaraima chain of tepuis (table-top mountain) or plateaux in South America. It is located at the junction of Brazil, Guyana and Venezuela. A characteristic large flat-topped mountain surrounded by cliffs 400–1,000 m (1,300–3,300 ft) high, its highest point is located on the southern edge of the cliff at an elevation of 2,810 m (9,220 ft) in Venezuela. Another protrusion at an elevation of 2,772 m (9,094 ft) at the junction of the three countries in the north of the plateau is the highest point in Guyana. The name Mount Roraima came from the native Pemon people. Roroi in the Pemon language means "blue-green", and ma means "great".

Leaching caused by intense rainfall has shaped the peculiar topography of the summit, and the geographical isolation of Mount Roraima has made it home to much endemic flora and fauna. Western exploration of Mount Roraima did not begin until the 19th century, when it was first climbed by a British expedition in 1884. Yet despite subsequent expeditions, its flora and geology remain largely unknown. The privileged setting and relatively easy access and climbing conditions on the south side of the cliffs make Mount Roraima a popular destination for hikers.

Mount Roraima is located in the Pacaraima Mountains in the eastern part of the Guiana Highlands, in northern South America. Its area is shared among three countries: Brazil to the east (5%), Guyana to the north (10%), and Venezuela to the south and west (85%). Access to Mount Roraima from the Venezuelan side is close to the road and relatively easy; however, for both Brazil and Guyana the area is completely isolated and can only be reached by a few days of forest hikes or small local airstrip.

Mount Roraima is a flat-topped mountain, typical of the Guyana Shield, with an elevation of about 1,200 m (3,900 ft) in the southeast and only about 600 m (2,000 ft) in the northwest. The south, southeast, east, northeast and northwest faces are all formed by straight cliffs up to about 1,000 m (3,300 ft) high. At the southern end of the mountain, part of the cliff has collapsed, forming a natural boulder. The base of the cliff is surrounded by steep slopes to the south and east, and the north and west sides form river valleys leading to the summit.

The top of Mount Roraima has a length of more than 10 km (6.2 mi), a maximum width of 5 km (3.1 mi), an area of about 33–50 km² (13–19 sq mi), an elevation of more than 2,200 m (7,200 ft), and an average elevation of 2,600–2,700 m (8,500–8,900 ft). The plateau is a pseudo-karst surface etched by heavy rainfall. The highest point is 2,810 m (9,219 ft) above sea level, located at the southern end of the plateau and the highest point in the state of Bolívar, 8.25 km (5.13 mi) north of the summit is another high point with an elevation of 2,772 m (9,100 ft), which is the highest point in Guyana. In the northern part of the plateau is the landmark of the border between Brazil, Venezuela and Guyana, with an elevation of 2,734 m (8,970 ft).

Due to its height and proximity to the equator, Mount Roraima has a constant average annual temperature between 20–22 °C (68–72 °F) and annual rainfall of more than 1,500 mm (59 in), with 1,800–3,000 mm (71–120 in) in parts of the rainy season from April to November. The climatic conditions at the top of the mountain differ significantly from its base, the high cloudiness in the region is associated with the prevailing northeasterly and southeasterly winds, and the relative humidity of the air remains between 75% and 85%.

Mount Roraima is composed of Proterozoic age sandstone formed about 1.7 to 2 billion years ago, and hence amongst the oldest rocks on Earth. It contains a large amount of quartz deposits, 98% are silica particles, forming white or pink crystals several centimeters long. These rocks sit on a granite and gneiss base and were originally covered by layers of Mesozoic clay, conglomerate, and diorite, but have been exposed by erosion and by orogeny over the past 180 million years, eroded by precipitation to form strange shapes. The soil of the sandstone matrix is highly acidic, poor in nutrients, and very fine. Intense rainfall prevents the fixation of nutrients and particles, thereby preventing the formation of hilltop vegetation and soil.

The numerous caves and rifts in the interior of the plateau make Mount Roraima exhibit a pseudo-karst structure, and these caves form a network over 15 km (9.3 mi) long, with a total height difference of 73.21 m (240.2 ft). It contains the largest quartz cave in the world, discovered by the Oxford University Cave Club and the Venezuelan Speleological Society. These caves are formed by the infiltration of surface water, so the water level inside them depends largely on the precipitation on the surface of the plateau: prolonged drought can dry up waterways, and dry caves can also become underground rivers. Water pours into the caves, rushes through crevices in the rock, and flows out as waterfalls on the mountainside, feeding numerous streams at the foot of the mountain.