relief and is characterized by abrupt changes in altitude. At one point the gorge measures deep and wide from rim to rim, and as a result is listed by the Guinness Book of Records as the deepest canyon in the world in proportion to its width, though some gorge lobbyists contest that claim. Steep slopes and precipitous rocky cliffs dominate in the middle and higher zones respectively. Numerous gullies dissect both sides of the gorge and the weathering action of water down its walls creates extended screes. The Vikos Gorge has been carved over millions of years by the Voidomatis river, a tributary of the Aoös. The Voidomatis is mostly seasonal, with year-round flow occurring only in the lower part of the gorge. Due to its nature, the area of the gorge is precipitous and impassable most of the year. As the Vikos Gorge is a deep cross section of the mountain, its slopes expose a series of rock formations of various ages. The upper layers, at a depth of 0–, consist of relatively young Eocene limestone, at a depth of – they consist of a stratum from the Campanian era, while below they consist of Jurassic and Cretaceous limestone. In the deepest layers, grey Jurassic dolomite is dominant. Sedimentary and lithological investigation in the Voidomatis basin revealed that the innermost alluvial deposits consist of limestone-derived material, carried by the Voidomatis river from higher elevations by glacial action about 30,000 years ago. The subsequent (middle) deposits are the product of de-glaciation and the extended run-off from the uplands about 20,000 years ago, while the outer unit is attributed to human activities associated with pastoralism, which caused extended deforestation and soil erosion. The Voidomatis basin contains evidence for three major phases of glaciation, with the two largest and earliest taking place during the Middle Pleistocene. The final phase of glacial activity probably occurred during the Last Glacial Maximum, between 22,000 and 20,000 ago. A special feature of the limestone, resulting from its weathering by water, is its karstic nature. During the large Middle Pleistocene glaciations, surface runoff from glacial meltwaters would have fed directly into the river channel network because much of the upland limestone terrain was covered by ice, and many conduits in the karst would have been choked with sediment or permanently frozen. As a result, the glacier snouts came close to the modern valley bottoms. In contrast, during