The Caucasus Mountains include the Greater Caucasus in the north and Lesser Caucasus in the south. The Greater Caucasus runs west-northwest to east-southeast, from the Caucasian Natural Reserve in the vicinity of Sochi on the northeastern shore of the Black Sea nearly to Baku on the Caspian Sea. The Lesser Caucasus runs parallel to the Greater about 100 km (62 mi) south. The Greater and Lesser Caucasus ranges are connected by the Likhi Range, and to the west and east of the Likhi Range lie the Colchis Plain and the Kur-Araz Lowland. The Meskheti Range is a part of the Lesser Caucasus system. In the southeast the Aras River separates the Lesser Caucasus from the Talysh Mountains which straddle the border of southeastern Azerbaijan and Iran. The Lesser Caucasus and the Armenian Highland constitute the Transcaucasian Highland, which at their western end converge with the highland plateau of Eastern Anatolia in the far north east of Turkey. The highest peak in the Caucasus range is Mount Elbrus in the Greater Caucasus, which rises to a height of 5,642 metres (18,510 ft) above sea level. Mountains near Sochi hosted part of the 2014 Winter Olympics.
Geologically, the Caucasus Mountains belong to a system that extends from southeastern Europe into Asia. The Greater Caucasus Mountains are mainly composed of Cretaceous and Jurassic rocks with the Paleozoic and Precambrian rocks in the higher regions. Some volcanic formations are found throughout the range. On the other hand, the Lesser Caucasus Mountains are formed predominantly of the Paleogene rocks with a much smaller portion of the Jurassic and Cretaceous rocks. The evolution of the Caucasus began from the Late Triassic to the Late Jurassic during the Cimmerian orogeny at the active margin of the Tethys Ocean while the uplift of the Greater Caucasus is dated to the Miocene during the Alpine orogeny.
The Caucasus Mountains formed largely as the result of a tectonic plate collision between the Arabian plate moving northwards with respect to the Eurasian plate. As the Tethys Sea was closed and the Arabian Plate collided with the Iranian Plate and was pushed against it and with the clockwise movement of the Eurasian Plate towards the Iranian Plate and their final collision, the Iranian Plate was pressed against the Eurasian Plate. As this happened, the entire rocks that had been deposited in this basin from the Jurassic to the Miocene were folded to form the Greater Caucasus Mountains. This collision also caused the uplift and the Cenozoic volcanic activity in the Lesser Caucasus Mountains.
The entire region is regularly subjected to strong earthquakes from this activity. While the Greater Caucasus Mountains have a mainly folded sedimentary structure, the Lesser Caucasus Mountains are largely of volcanic origin.
The Javakheti Volcanic Plateau in Georgia and the surrounding volcanic ranges which extend well into central Armenia are some of the youngest features of the region. Only recently was the Caucasus a scene for intense volcanic activity: the Armenian highland was flooded by calc-alkaline basalts and andesites in the Pliocene and the highest summits of the Caucasus, the Elbrus, and the Kazbek, formed as Pleistocene-Pliocene volcanoes. The Kazbek is no longer active, but the Elbrus erupted in postglacial times and fumarole activity is registered near its summit. Contemporary seismic activity is a prominent feature of the region, reflecting active faulting and crustal shortening. Clusters of seismicity occur in Dagestan and in northern Armenia. Many devastating earthquakes have been documented in historical times, including the Spitak earthquake in December 1988 which destroyed the Gyumri-Vanadzor region of Armenia.