Africa’s semi-arid Sahel region is a crucible of climate change, population movement, and jihadist attacks. Here is a brief explainer on the region ahead of key elections in Niger on Sunday: Wedged between the desert to the north and tropical forests and savannah to the south, the belt has a tropical semi-arid climate.

The Sahel is a narrow band of semi-arid land that forms a transition zone between the Sahara to the north and the savannas to the south. It is made up of flat, barren plains that stretch roughly 5,400 kilometers (3,300 miles) across Africa, from Senegal to Sudan.

Africa has eight major physical regions: the Sahara, the Sahel, the Ethiopian Highlands, the savanna, the Swahili Coast, the rain forest, the African Great Lakes, and Southern Africa.

Sudan, the vast tract of open savanna plains extending across Africa between the southern limits of the Sahara (desert) and the northern limits of the equatorial rain forests. The term derives from the Arabic bilād al-sūdān (“land of the black peoples”) and has been in use from at least the 12th century.

The answer lies in the climate of the Arctic and northern high latitudes. However, around 5,500 years ago there was a sudden shift in climate in northern Africa leading to rapid acidification of the area. What was once a tropical, wet, and thriving environment suddenly turned into the desolate desert we see today.

Precipitation in the Sahara ranges from zero to about 3 inches of rain per year, with some locations not seeing rain for several years at a time.

We don’t own the Sahara desert. The Sahara is “owned” by Africans in at least 11 countries. Many of those countries are not exactly paragons of political stability (e.g. Sudan, Egypt, Libya, Sudan, Tunisia).

The sand is primarily derived from weathering of Cretaceous sandstones in North Africa. When these sandstones were deposited in the Cretaceous, the area where they are now was a shallow sea. The original source of the sand was the large mountain ranges that still exist in the central part of the Sahara.

The depth of sand in ergs varies widely around the world, ranging from only a few centimeters deep in the Selima Sand Sheet of Southern Egypt, to approximately 1 m (3.3 ft) in the Simpson Desert, and 21–43 m (69–141 ft) in the Sahara.

What Is Underneath the Sand? Roughly 80% of deserts aren’t covered with sand, but rather show the bare earth below—the bedrock and cracking clay of a dried-out ecosystem. Without any soil to cover it, nor vegetation to hold that soil in place, the desert stone is completely uncovered and exposed to the elements.

However, desert sand has little use; the grains are too smooth and fine to bind together, so it is not suitable for the making of for instance concrete. This sand is not used in construction, as its grains are too smooth and fine to bind together for building materials.

Antarctic desert

Beneath the sands of the Sahara Desert scientists have discovered evidence of a prehistoric megalake. Formed some 250,000 years ago when the Nile River pushed through a low channel near Wadi Tushka, it flooded the eastern Sahara, creating a lake that at its highest level covered more than 42,000 square miles.

Often, underneath the loose sand of a beach is a layer of hard, compacted sand, which could be on its way to becoming sandstone if the necessary cement, pressure and heat ever appear — and if is not eroded by severe storms. These beaches commonly lose all the new sand in five years or so.

Once a region becomes arid, there’s no vegetation or water to hold the soil down. Then the wind takes over and blows away the finer particles of clay and dried organic matter. What’s left is desert sand. Sometimes an entire desert has migrated due to movement of Earth’s huge overlying land plates.

It does not have very many uses, but it is soil. There may be different textures as you move down the soil horizons, however it is very likely that it’s sand all the way down to the bedrock. Nope. Soil is a mixture of minerals and decoposing plants.

Sand absorbs very little water because its particles are relatively large. The other components of soils such as clay, silt and organic matter are much smaller and absorb much more water. Increasing the amount of sand in the soil reduces the amount of water that can be absorbed and retained.

Sand does not hold any water and clay particles hold water so tightly to the particle surface that plant roots are unable to extract it from the soil. Silty soils are also heavier than sandy soils, and holds up nutrients and make it better for crop cultivation.