Richat Structure (Eye of the Sahara)
Adrar
The Richat Structure, also called Guelb er Richât or the Eye of Africa, is a striking circular geological formation located on the Adrar Plateau in Mauritania's Sahara Desert. Measuring approximately 40 kilometers in diameter, it is an eroded geological dome formed by a subsurface igneous intrusion that uplifted and deformed sedimentary rock layers, exposing concentric rings with the oldest rocks at the center. The exposed rocks range in age from Late Proterozoic at the core to Ordovician sandstone at the edges. The structure features various igneous rocks including rhyolites, gabbros, carbonatites, and kimberlites, some hydrothermally altered, indicating complex volcanic and intrusive activity around 94 to 104 million years ago. Its central megabreccia, a thick siliceous breccia formed by hydrothermal dissolution and collapse, adds to its geological uniqueness. The site is also notable for exceptional Acheulean Paleolithic stone tools, highlighting its archaeological importance. Recognized as one of the 100 geological heritage sites by the International Union of Geological Sciences, the Richat Structure captivates scientists and visitors alike with its enigmatic formation and vast scale.
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Tip: Visitors should plan their trip during cooler months to avoid extreme desert heat. Due to its remote location, arranging guided tours or transport in advance is recommended. There are no formal entrances or facilities, so adequate preparation for desert conditions is essential. Purchasing any permits or local guides beforehand can enhance the experience. Discounts or tickets are generally not applicable as it is a natural feature accessible freely from afar but requires logistical planning for close approach.
Interesting facts
- •The Richat Structure is approximately 40 kilometers (25 miles) in diameter, making it visible from space.
- •It is composed of concentric rings of sedimentary and igneous rocks, with the oldest rocks exposed at the center.
- •Hydrothermal alteration created a central megabreccia at least 40 meters thick in some areas.
- •The structure contains exceptional accumulations of Acheulean Paleolithic stone tools, indicating ancient human activity.
- •It was designated as one of the 100 geological heritage sites by the International Union of Geological Sciences (IUGS).
History
The Richat Structure was formed by geological processes over millions of years, with sedimentary rocks dating back to the Late Proterozoic and Ordovician periods.
Around 94 to 104 million years ago, a large alkaline igneous intrusion uplifted the overlying sedimentary layers, creating a dome that was subsequently eroded to reveal concentric rings.
Hydrothermal activity about 98 million years ago caused significant alteration and collapse in the center, forming a megabreccia.
The site has been known locally for centuries and was scientifically studied in modern times, gaining recognition as a geological heritage site due to its unique formation and scientific value.
Place Guide
Concentric Rings
The Richat Structure's defining feature, these concentric rings are formed by differential erosion of sedimentary and igneous rock layers, revealing a pattern of circular cuestas visible from aerial views.
Central Megabreccia~98 million years ago
A thick siliceous breccia formed by hydrothermal dissolution and collapse, creating a chaotic assemblage of fractured rocks at the center of the structure.
Igneous Intrusions94-104 million years ago
Various intrusive rocks such as rhyolites, gabbros, carbonatites, and kimberlites are exposed within the structure, evidencing a large alkaline igneous intrusion beneath the dome.
