An escarpment (or scarp) is a long, steep slope or line of cliffs that separates two areas of land at different heights, usually marking the edge of a plateau or a tilted layer of hard rock. Escarpments form in two main ways: movement along a geological fault, or erosion that strips away soft rock from beneath a harder cap, and the largest, such as Southern Africa's Great Escarpment, run for thousands of kilometres.
The word comes from the Italian scarpa, the sloping wall at the base of a fortification, and the image fits: from below, an escarpment looks like a rampart; from above, it often looks like nothing at all, because the land on top is flat or tilts gently away from the edge. That lopsided profile is the key to recognising one.
Reading the Shape: Scarp Face, Crest and Dip Slope
Most escarpments have three parts. The scarp face is the steep side, sometimes a sheer cliff, sometimes a series of steps and talus slopes. The crest or brow is the sharp break at the top. Behind it lies the back slope, which in layered rock is called the dip slope because it follows the angle at which the rock beds dip into the ground.
Geographers distinguish a few related forms by how that back slope behaves:
- Cuesta (Spanish for "slope"): a ridge with one steep scarp face and one long, gentle dip slope, formed where rock layers tilt only a few degrees. The Niagara Escarpment is a cuesta.
- Hogback: a narrow ridge on steeply tilted beds, so both sides are steep. The Dakota Hogback along the Colorado Front Range is the textbook case.
- Plateau edge: where horizontal rock ends abruptly, as at the rim of a tableland. Many of Africa's and India's great escarpments are this type.
England is full of small cuestas. The limestone of the Cotswolds tilts gently east toward Oxford but ends in a steep western scarp overlooking the Severn Vale, and the chalk of the Chilterns and the North and South Downs does the same, each with a "scarp slope" facing one way and a long "dip slope" facing the other. Villages cluster at the foot of these scarps, where water that has soaked through the porous chalk or limestone emerges as a line of springs.
Escarpments also come in staircases. In southern Utah and northern Arizona, the Grand Staircase climbs from the Grand Canyon's rim in a series of retreating cliffs, the Chocolate, Vermilion, White, Gray and Pink Cliffs, each carved from a different rock formation, rising roughly 1,800 m in total from bottom to top.
Two Ways to Build One: Faults and Stripped Rock
Fault scarps
When the crust breaks along a fault and one block moves up or down relative to the other, the exposed edge is a fault scarp. Young ones can appear in seconds: the magnitude 7.3 Hebgen Lake earthquake in Montana in 1959 opened fresh scarps up to about 6 m high. Repeated movement over millions of years builds much larger ones. The steep eastern face of the Sierra Nevada, rising above Owens Valley in California, and the Wasatch Front behind Salt Lake City are both fault escarpments, and the walls of the East African Rift, such as the Mau Escarpment in Kenya, drop more than 1,000 m in places. For how these fractures work, see our explainer on what a fault line is.
Fault scarps also shape where water surfaces. The Balcones Escarpment in central Texas follows a zone of ancient faults that divides the limestone Hill Country from the flat coastal plain. Water moving through the Edwards Aquifer rises along those faults as large springs, at San Marcos, New Braunfels (Comal Springs) and San Antonio, which is exactly why a line of towns grew up along the scarp foot.
Erosion scarps
Far more escarpments are made by erosion. Where a hard layer (sandstone, dolostone, basalt) sits on a softer one (shale, clay), water and frost eat into the soft rock faster, undermining the cap until blocks break off. The cliff face therefore retreats, keeping its steep shape while moving slowly back across the landscape. Some have moved tens or even hundreds of kilometres from where they began.
The Niagara Escarpment, Traced Across Four States and a Province
North America's best-known escarpment runs for roughly 1,600 km in an arc from western New York through southern Ontario, around the northern shores of Lakes Huron and Michigan, and down through Wisconsin's Door Peninsula into Illinois. Its cap is resistant Silurian dolostone, laid down in a warm sea more than 420 million years ago, overlying softer shales.
Niagara Falls is the escarpment in action. The Niagara River drops over the dolostone cap, undercuts the shale below, and the lip collapses, so the falls have retreated about 11 km upstream in roughly 12,500 years, cutting the Niagara Gorge behind them. In Ontario the escarpment's woods and cliffs were designated a UNESCO World Biosphere Reserve in 1990, and the Bruce Trail, Canada's oldest long-distance footpath, follows it for roughly 900 km from Niagara to Tobermory. Our Niagara Falls geography guide explains the falls' retreat in more detail.
Africa's Great Escarpment and the Drakensberg
Southern Africa is rimmed by one of the largest escarpments on Earth. The Great Escarpment runs for about 5,000 km, roughly parallel to the coast, from Angola and Namibia around South Africa and up into Zimbabwe, separating a high interior plateau from a narrow coastal lowland. It began forming when Gondwana broke apart from about 180 million years ago: the new continental margins were uplifted, and erosion has been driving the edge inland ever since.
Its highest section is the Drakensberg, pictured above, where a thick cap of basalt lava laid down around 180 million years ago forms walls well over 1,000 m high. Thabana Ntlenyana in Lesotho, at 3,482 m, is the highest point in southern Africa, and the Tugela Falls pour roughly 948 m off the escarpment edge in a series of drops. The uKhahlamba-Drakensberg Park was listed by UNESCO in 2000 for both its scenery and its San rock art. Further north, the Blyde River Canyon cuts through the same escarpment in Mpumalanga.
Escarpment, Cliff or Mountain Range? Telling Them Apart
Escarpments are easy to confuse with two similar features, and the difference comes down to what lies on either side.
- A cliff is any near-vertical rock face, of any length. A sea cliff may be a few hundred metres long. An escarpment is defined by separating two landscapes at different levels over a long distance; it may include cliffs, but many escarpments are steep slopes rather than sheer walls.
- A mountain range rises above the land on both sides. An escarpment does not: climb to the top of the Drakensberg or the Western Ghats and you step onto a plateau that stays high. That is why these "mountains" look dramatic from the coast and underwhelming from inland.
- A bluff is a steep bank, usually beside a river or floodplain, cut by the river's own erosion. It is local; an escarpment is regional.
India's Western Ghats show the distinction well. Seen from the Konkan and Malabar coasts they are a mountain wall roughly 1,600 km long, rising to 2,695 m at Anamudi, but they are really the uplifted western edge of the Deccan Plateau, left behind after India split from Madagascar about 88 million years ago. Our Western Ghats guide covers that range.
Why Escarpments Matter to the People Living Beside Them
Because they rise abruptly, escarpments catch rain. Moist air from the Arabian Sea is forced up the Western Ghats, dropping several metres of monsoon rain on the western slopes while the Deccan beyond sits in a rain shadow. The same effect gives the eastern Drakensberg its lush grassland and the interior plateau its drier Highveld.
They have also been barriers and refuges. In Mali, the Bandiagara Escarpment, a sandstone cliff about 150 km long and up to around 500 m high, sheltered first the Tellem people, whose cliff dwellings survive in its face, and then the Dogon, whose villages sit on its scree slopes; the area was inscribed by UNESCO in 1989. Near Sydney, the sandstone escarpments of the Blue Mountains blocked European settlers from the interior until 1813. And engineers have spent fortunes getting across them: the Bhor Ghat railway, opened in 1863, needed a zigzag reversing station to climb the Western Ghats between Mumbai and Pune.
In Arizona, the Mogollon Rim, the southern edge of the Colorado Plateau, runs for about 320 km as a wall of sandstone and limestone several hundred metres high. It marks a sharp boundary in climate and vegetation, with ponderosa pine forest on top and chaparral and desert grassland below, and it drives summer thunderstorms that make the rim one of the most lightning-struck and wildfire-prone parts of the state.
Escarpments are not only a land feature, either. The continental slope, where the shallow continental shelf drops to the deep ocean floor, is the largest escarpment system on the planet, and similar scarps have been mapped on Mars and Mercury. Wherever two surfaces meet at different levels along a steep edge, a geographer will call it by the same name.