A giant, geological wonder in the Sahara Desert of Mauritania is pictured in this satellite image.
The 40 km-diameter circular Richat structure is one of the geological features that is easier to observe from space than from down on the ground, and has been a familiar landmark to astronauts since the earliest missions.
Once thought to be the result of a meteor impact, researchers now believe it was caused by a large dome of molten rock uplifting and, once at the surface, being shaped by wind and water into what we see today. Concentric bands of resistant quartzite rocks form ridges, with valleys of less-resistant rock between them.
The dark area on the left is part of the Adrar plateau of sedimentary rock standing some 200 m above the surrounding desert sands. A large area covered by sand dunes – called an erg – can be seen in the lower-right part of the image, and sand is encroaching into the structure’s southern side.
Zooming in on the southern side of the bullseye, we can see individual trees and bushes as tiny dots. These follow a river-like structure that appears to have been dry when this image was acquired, a few weeks after the rainy season. Some areas to the south and east of the Richat appear to be covered with temporary lakes, which are dry for most of the year.
This image, also featured on the Earth from Space video program, was acquired on 23 November 2010 by the Advanced Visible and Near Infrared Radiometer on Japan’s ALOS satellite.
Image credit: JAXA/ESA
This image from Japan’s ALOS satellite shows the Aorounga Crater in northern Chad.
The crater is just south of the Tibesti Mountains, a range of inactive – with some potentially active – volcanoes in the central Sahara desert.
Measuring about 12 km across, the crater was created by a meteorite impact about 340 million years ago.
Clearly visible is the dark, central peak, caused by material splashing up after the impact, similar to how water bounces back up when a stone is thrown in. This peak is surrounded by a low, sand-filled ring, which is surrounded by another ring of rock from when the material was thrown outwards. A distinctive low, sand-filled trough circles the others – the outer edges of the initial impact.
The linear rock ridges that run diagonally across this image are ‘yardangs’ and are formed by wind erosion. Here, we can clearly see how the wind blows from northeast to southwest. Sand dunes form in the wind-cut valleys between the rock ridges of the yardangs.
Japan’s Advanced Land Observation Satellite captured this image on 3 November 2010. ALOS was supported as a Third Party Mission, which means that ESA used its multimission ground systems to acquire, process, distribute and archive data from the satellite to its user community.
This image is featured on the Earth from Space video program.
Photo credit: JAXA/ESA
The Dasht-e Lut salt desert in southeast Iran is captured in this Envisat image.
The desert is often called the ‘hottest place on Earth’ as satellites measured record surface temperatures there for several years. The highest land surface temperature ever recorded was in the Lut Desert in 2005 at 70.7ºC, as measured by NASA’s Aqua satellite.
The light area in the center of the image are the long, parallel wind-carved ridges and furrows. The darker area to the east is an extent of massive sand dunes, some reaching up to 300 m tall.
In the upper-right section we can see a light green, shallow body of water that straddles Iran’s border with Afghanistan. With their arid surroundings, the wetlands in this border region have been a major source of food and fresh water for thousands of years, as well as an important stop for migratory birds. But irrigation expansion combined with droughts have caused the water levels in these wetlands to drop significantly – and some years even dry up.
In the lower-left we can see the white, snow-capped Jebal Barez mountains.
A major earthquake struck about 100 km east of the snow-caps in 2003, its epicenter near the ancient city of Bam (lower-central portion of image). Iran experiences frequent tectonic activity as several major fault lines cross the country.
This image was acquired by Envisat’s MERIS instrument on 2 April 2012 and is also featured on the Earth from Space video program.
Photo credit: ESA
