Valley, Canyon, and Basin Landforms

A valley is a long, low area of land between hills or mountains, usually carved by a river or glacier; a canyon is a deep, narrow valley with steep rock walls; and a basin is a large depression in the land surface, either one that drains toward a common outlet (a drainage basin) or one that is enclosed. In brief: river valleys are typically V-shaped, glacial valleys U-shaped. Canyons form where a river cuts down rapidly through resistant rock, as the Colorado River has done in the Grand Canyon (about 446 km long and up to about 1,800 m deep). Basins include river basins (the Amazon basin covers about 6 million km²), structural basins and desert basins. Cliffs are steep rock faces formed by erosion or faulting.

These landforms record the work of rivers, ice and tectonic forces, and are home to many of the world’s farms and cities. This guide describes valleys, canyons, basins and cliffs, compares them in a table, works through calculations of river gradient and erosion rate, outlines their history and corrects common mistakes.

What are valleys?

Valleys are the most common landforms made by running water or ice. River valleys are formed mainly by erosion: in the upper course a fast, steep stream cuts down vertically (vertical erosion) and makes a narrow, V-shaped valley with interlocking spurs; further downstream the river erodes sideways, meanders and builds a wide, flat floodplain. Glacial valleys are carved by glaciers into a broad U-shape with steep sides and a flat floor, and often have hanging valleys (tributaries left high above the main valley, where waterfalls form), and may contain long narrow lakes. Rift valleys form where blocks of crust drop down between faults, as in the East African Rift Valley. Valleys often hold fertile soils, water and transport routes, which is why many settlements are located in them.

What are canyons and cliffs?

A canyon (or gorge) has steep, often stepped walls and a narrow floor; it forms where a river cuts down faster than the walls are weathered, which happens in areas of uplift, resistant rock and dry climates, as the rock walls stay steep. Famous examples: the Grand Canyon in Arizona (cut by the Colorado River through the Colorado Plateau), the Fish River Canyon in Namibia, the Yarlung Tsangpo Grand Canyon in Tibet, and the Copper Canyon in Mexico. Some canyons, such as slot canyons, are extremely narrow. A cliff is a vertical or very steep rock face. Cliffs form by erosion of the sea (sea cliffs), by faulting (fault scarps), by glaciers or by rivers undercutting the bank, and where a hard rock layer lies over a soft layer, which erodes faster. An escarpment is a long cliff-like ridge with a steep face on one side and a gentle slope on the other.

What are basins?

The word “basin” has several meanings in geography. A drainage basin (river basin or catchment) is the area drained by a river and its tributaries, separated from the neighboring basins by a divide or watershed: the Amazon basin is about 6.1 million km², the Congo basin about 3.7 million km². A structural basin is a depression formed by down-warping of the crust or by faulting, often filled with sediment, which can contain oil, gas or groundwater (the Paris Basin, the Great Artesian Basin of Australia). An endorheic (closed) basin has no outlet to the sea, so water ends up in a lake or evaporates, such as the Great Basin in the western United States or the Dead Sea, whose shore is the lowest land on Earth (roughly 430 m below sea level). An ocean basin is the huge depression holding the ocean water.

Valleys, canyons and basins compared

Worked example: gradient and erosion rate

1. River gradient: a river falls from 1,200 m at its source to sea level over a course of 400 km. The gradient is 1,200 ÷ 400 = 3 m per km, or 0.3 percent, which is an angle of arctan(0.003) = 0.17°. Most of the fall is in the steep upper course, so the lower course has an even smaller gradient.
2. Canyon downcutting: if a canyon about 1,800 m deep was cut over roughly 5 million years (estimates for the Grand Canyon vary, and some are 5–6 million years), the average downcutting rate is 1,800,000 mm ÷ 5,000,000 yr = 0.36 mm per year; with 6 million years it is 0.30 mm per year, about the thickness of a few sheets of paper per year.
3. Shape of the Grand Canyon: the canyon is about 446 km long and up to about 29 km wide, so its length is about 446 ÷ 29 = 15 times its greatest width.
4. Drainage basins: the Amazon basin (6.1 million km²) is 6.1 ÷ 3.7 = 1.65 times the size of the Congo basin.
5. Area drained and rainfall: a basin of 10,000 km² receiving 800 mm of rain a year gets 10,000 × 10⁶ m² × 0.8 m = 8 × 10⁹ m³ of water a year. If 40 percent runs off into the river, the average discharge is 3.2 × 10⁹ m³ per year, which is 3.2 × 10⁹ ÷ 31.5 × 10⁶ s = about 100 m³ per second.

How have these landforms influenced people?

River valleys were the cradle of ancient civilizations, with fertile floodplains for farming. Canyons and gorges often hold natural routes or barriers, and they have been used for dams and hydroelectric power, such as the Hoover Dam in the Black Canyon of the Colorado. Sedimentary basins contain much of the world’s coal, oil and gas. The study of the rocks in the Grand Canyon, from the 19th century, helped scientists to understand geological time. Glacial valleys such as those in Norway and Switzerland have become centers of settlement and tourism.

Which mistakes are common?

Mistake 1: Thinking that all valleys were carved by the rivers that now flow in them

Many were carved by glaciers or formed by tectonic movement, and the present stream may be too small for the valley.

Mistake 2: Mixing up V-shaped and U-shaped valleys

V-shaped valleys are river valleys, and U-shaped valleys are glacial.

Mistake 3: Using “basin” only for river basins

It can also refer to structural, closed and ocean basins.

Mistake 4: Assuming a canyon always formed quickly

Even the Grand Canyon took millions of years, at an average rate of a fraction of a millimeter per year.