The Trango Towers in Pakistan. Their vertical faces are the world's tallest cliffs. Trango Tower center; Trango Monk center left; Trango II far left; Great Trango right.
Most cliffs have some form of scree slope at their base. In arid areas or under high cliffs, these are generally exposed jumbles of fallen rock. In areas of higher moisture, a soil slope may obscure the talus.
Many cliffs also feature tributarywaterfalls or rock shelters. Sometimes a cliff peters out at the end of a ridge, with tea tables or other types of rock columns remaining.
Given that a cliff need not be exactly vertical, there can be ambiguity about whether a given slope is a cliff or not, and also about how much of a certain slope to count as a cliff. (For example, given a truly vertical rock wall above a very steep slope, one could count only the rock wall, or the combination.) This makes listings of cliffs an inherently uncertain endeavor.
The highest cliff (rock wall, mountain face) in the world, is Nanga Parbat in the Himalayas, that rises 4600 meters above its base.
According to some sources, the highest cliff in the world, about 1,340 m high, is the east face of Great Trango in the Karakoram mountains of northern Pakistan. (This uses a fairly stringent notion of cliff, as the 1,340 m figure refers to a nearly vertical headwall; adding in a very steep approach brings the total height to over 1,600 m.) The highest sea cliffs, 1,010 m high, are located at Kalaupapa, Hawaii[1]. (This uses a less stringent definition, as the average slope of these cliffs is about 1.7, corresponding to an angle of 60 degrees.)
Considering a truly vertical drop, Mount Thor on Baffin Island in ArcticCanada is the highest at 1,370 m (4,500 ft) high in total (the top 480 m (1,600 ft) is overhanging). This is said to give it the longest purely vertical drop on Earth at 1,250 m (4,100 ft).
Given that walking over a cliff could be fatal, the Ordnance Survey distinguish between cliffs (continuous line along the top edge with projections down the face) and outcrops (continuos line along lower edge).
Nanga Parbat, highest cliff (rock wall, mountain face) in the world
Mount Thor, Baffin Island, Canada; 1,370 m (4,500 ft) total; top 480 m (1,600 ft) is overhanging. This reputedly gives it the largest purely vertical drop on Earth at 1,250 m (4,100 ft).