The Sahara, a vast expanse of North Africa, is the world’s largest sand desert. It stands as the largest hot desert on the planet and the third largest overall, exceeded only by the cold deserts of Antarctica and the Arctic. While the Sahara is famous for its towering dune fields, often referred to as sand seas, these sandy regions represent only a fraction of its total territory. Its size, approximately 9.2 million square kilometers (3.6 million square miles), ensures that its isolated sandy areas collectively form the most extensive system of sand dunes in the world.
Defining the Sand Desert (Erg)
A desert is technically defined by its lack of precipitation, typically receiving less than 250 millimeters of rain annually. This classification, based on aridity, includes environments like the ice-covered regions of the poles, which are considered cold deserts.
A “sand desert” refers to a specific type of terrain characterized by a surface primarily covered with vast, wind-swept sand dunes. Geographers use the term erg to describe such areas, which are also known as sand seas. An erg is officially designated when sand covers more than 20% of the surface area.
Sand dunes cover only about 20% to 25% of the Sahara’s total surface. The majority consists of rocky plateaus, known as hamadas, and gravel plains, called regs. Despite this, the Sahara contains multiple enormous ergs, such as the Great Western Erg and the Great Eastern Erg, making it the largest collection of sandy deserts globally. For comparison, the Rub’ al Khali in the Arabian Peninsula is one of the world’s largest continuous ergs.
The Sahara’s Geographical Extent and Location
Stretching across the northern third of the African continent, the Sahara is comparable in size to the entire continental United States. This immense territory spans approximately 11 different countries.
The desert’s expanse from west to east is approximately 4,800 kilometers, and its width from north to south ranges between 1,200 and 1,800 kilometers. This vast territory encompasses nearly 31% of the entire African landmass.
Countries of the Sahara
The Sahara spans the territories of:
- Algeria
- Chad
- Egypt
- Libya
- Mali
- Mauritania
- Morocco
- Niger
- Sudan
- Tunisia
- Western Sahara (disputed territory)
The Sahara’s boundaries are defined by major geographical features that frame the North African landmass. To the west, the desert meets the Atlantic Ocean, while the Red Sea forms its eastern boundary. The northern edge is delineated by the Mediterranean Sea coast and the Atlas Mountains.
The southern boundary is marked by a transitional zone of semi-arid grassland known as the Sahel. This boundary is a shifting ecological belt where the desert slowly gives way to savanna, often following the 200-millimeter annual rainfall line. This geographical positioning places the Sahara under the subtropical ridge, a high-pressure belt that prevents the formation of rain-producing clouds.
Unique Features of the Sahara’s Sand Seas
The ergs within the Sahara exhibit a variety of complex landforms sculpted by constant wind action, a process known as aeolian transport. The largest dunes often reach heights of 180 meters (nearly 600 feet), though some massive sand ridges, called draa, can be even taller. These structures are continually being reshaped by the prevailing winds.
The sandy areas feature distinct dune types, each reflecting the direction and strength of the wind. Crescent-shaped dunes, or barchans, are common in areas with a steady, moderate wind from one direction. Where wind patterns are more complex or shifting, massive star dunes form with multiple arms radiating from a central pyramid. Long, straight ridges called seifs, or linear dunes, dominate areas with two primary wind directions.
The desert environment is characterized by extreme temperature fluctuations, which are intensified by the sandy surface. During the day, temperatures can regularly exceed 45°C (113°F), with the surface sand itself reaching up to 80°C (176°F). The lack of humidity and cloud cover causes this heat to radiate quickly into space after sunset, resulting in dramatic temperature drops at night, sometimes approaching the freezing point in the winter.
Despite the arid conditions, these sand seas contain hydrological features that sustain life. Scattered throughout the ergs are oases, which are fertile areas where water from ancient subterranean reserves reaches the surface. These water sources are often fed by vast, deep aquifers, formed by rainfall that occurred thousands of years ago when the Sahara was a much wetter environment.