Karst in the context of "Adriatic Sea"

The Balkan mountain range is located in the eastern part of the Balkan peninsula in Southeastern Europe. It is conventionally taken to begin at the peak of Vrashka Chuka on the border between Bulgaria and Serbia. It then runs for about 560 kilometres (350 mi), first in a south-easterly direction along the border, then eastward across Bulgaria, forming a natural barrier between the northern and southern halves of the country, before finally reaching the Black Sea at Cape Emine. The mountains reach their highest point with Botev Peak at 2,376 metres (7,795 ft).

In much of the central and eastern sections, the summit forms the watershed between the drainage basins of the Black Sea and the Aegean. A prominent gap in the mountains is formed by the predominantly narrow Iskar Gorge, a few miles north of the Bulgarian capital, Sofia. The karst relief determines the large number of caves, including Magura, featuring the most important and extended European post-Palaeolithic cave painting, Ledenika, Saeva dupka, Bacho Kiro, etc. The most notable rock formation are the Belogradchik Rocks in the west.

Limestone is a type of carbonate sedimentary rock which is the main source of the material lime. It is composed mostly of the minerals calcite and aragonite, which are different crystal forms of calcium carbonate CaCO₃. Limestone forms when these minerals precipitate out of water containing dissolved calcium. This can take place through both biological and nonbiological processes, though biological processes, such as the accumulation of corals and shells in the sea, have likely been more important for the last 540 million years. Limestone often contains fossils which provide scientists with information on ancient environments and on the evolution of life.

About 20% to 25% of sedimentary rock is carbonate rock, and most of this is limestone. The remaining carbonate rock is mostly dolomite, a closely related rock, which contains a high percentage of the mineral dolomite, CaMg(CO₃)₂. Magnesian limestone is an obsolete and poorly defined term used variously for dolomite, for limestone containing significant dolomite (dolomitic limestone), or for any other limestone containing a significant percentage of magnesium. Most limestone was formed in shallow marine environments, such as continental shelves or platforms, though smaller amounts were formed in many other environments. Much dolomite is secondary dolomite, formed by chemical alteration of limestone. Limestone is exposed over large regions of the Earth's surface, and because limestone is slightly soluble in rainwater, these exposures often are eroded to become karst landscapes. Most cave systems are found in limestone bedrock.

43°12′16″N 23°29′28″E / 43.20444°N 23.49111°E / 43.20444; 23.49111

Ledenika (Bulgarian: Леденика, English: icy or glacial) is a cave in the Northwestern parts of the Balkan Mountains, 16 km away from the Bulgarian city of Vratsa. Its entrance is approximately 830 m above sea level. The cave features an abundance of galleries and impressive karst formations including stalactites and stalagmites. It was first discovered around the beginning of the 20th century and has been open to tourists since 1961. Ledenika Peak on Graham Land in Antarctica is named after the cave, in recognition of its cultural importance.

The Rhodopes (/ˈrɒdəpiːz/; Bulgarian: Родопи, Rodopi; Greek: Ροδόπη, Rodopi; Turkish: Rodoplar) are a mountain range in Southeastern Europe, and the largest by area in Bulgaria, with over 83% of its area in the southern part of the country and the remainder in Greece. Golyam Perelik is its highest peak at 2,191 meters (7,188 ft). The mountain range gives its name to the terrestrial ecoregion Rodope montane mixed forests that belongs in the temperate broadleaf and mixed forests biome and the Palearctic realm. The region is particularly notable for its karst areas with their deep river gorges, large caves and specific sculptured forms, such as the Trigrad Gorge.

A significant part of Bulgaria's hydropower resources are located in the western areas of the range. There are a number of hydro-cascades and dams used for electricity production, irrigation, and as tourist destinations.

Cetinje (Montenegrin Cyrillic: Цетиње, pronounced [t͡sětiɲe]) is a town in Montenegro. It is the former royal capital (Montenegrin: prijestonica / приjестоница) of Montenegro and is the location of several national institutions, including the official residence of the president of Montenegro.

According to the 2023 census, the town had a population of 12,460 while the Cetinje Municipality had 14,465 residents. Cetinje is the centre of Cetinje Municipality. The city rests on a small karst plain surrounded by limestone mountains, including Mount Lovćen, the legendary mountain in Montenegrin historiography. Cetinje was founded in the 15th century and became a cradle of the culture of Montenegro. Its status as the honorary capital of Montenegro is due to its heritage as a long-serving former capital of Montenegro.

An atoll (/ˈæt.ɒl, -ɔːl, -oʊl, əˈtɒl, -ˈtɔːl, -ˈtoʊl/) is a ring-shaped island, including a coral rim that encircles a lagoon. There may be coral islands or cays on the rim. Atolls are located in warm tropical or subtropical parts of the oceans and seas where corals can develop. Most of the approximately 440 atolls in the world are in the Pacific Ocean.

Two different, well-cited models, the subsidence model and the antecedent karst model, have been used to explain the development of atolls. According to Charles Darwin's subsidence model, the formation of an atoll is explained by the sinking of a volcanic island around which a coral fringing reef has formed. Over geologic time, the volcanic island becomes extinct and eroded as it subsides completely beneath the surface of the ocean. As the volcanic island subsides, the coral fringing reef becomes a barrier reef that is detached from the island. Eventually, the reef and the small coral islets on top of it are all that is left of the original island, and a lagoon has taken the place of the former volcano. The lagoon is not the former volcanic crater. For the atoll to persist, the coral reef must be maintained at the sea surface, with coral growth matching any relative change in sea level (sinking of the island or rising oceans).