The Earth has many land areas covered by sand. Specifically, deserts are places where a significant amount of sand accumulates. The sand in the desert is so abundant that it is often likened to “rivers” and even “oceans.” When we mention deserts, we cannot overlook the Sahara, the largest desert in the world.
How is the Depth of the Sahara Measured?
The Sahara Desert was formed approximately 2.5 million years ago. It spans almost all of North Africa, extending across 12 countries: Algeria, Chad, Egypt, Libya, Mali, Morocco, Eritrea, Sudan, Tunisia, Western Sahara, and Niger. It is about 1,600 km wide from north to south and 5,600 km long from east to west, covering an area of over 9,000,000 km2, which accounts for 32% of the total area of Africa. The Sahara truly lives up to its title as the largest desert. According to scientists, the Sahara Desert is continuously expanding. Since 1962, it has grown by nearly 650,000 km2.
The Sahara Desert is one of the largest deserts in the world. (Photo: Baidu).
However, while we know its length and width, how deep is the Sahara Desert? If we were to excavate all the sand from the Sahara, what would we find underneath?
In fact, for relatively shallow deserts, we can measure depth using drills or directly excavating with excavators. However, with the large scale of the Sahara Desert, these methods are not feasible; drilling equipment could easily become buried in the sand.
Scientists have proposed an alternative method: using radar technology to measure the depth of the Sahara Desert. Specifically, depth sensors emit electromagnetic waves that travel to the sand surface. The waves then hit the sand surface to be measured and reflect back to the sensor. The sensor processes and calculates the data, providing accurate and quick measurements.
In reality, the depth of the desert also depends on other factors such as formation time, terrain, wind direction, and strength. In areas with many sand dunes, the depth can change with the movement of the sand. Therefore, we can say that the depth of the Sahara Desert is not fixed. Using radar technology allows for easy measurements of varying depths across different locations in the Sahara Desert.
Excavators cannot be used to measure the depth of the Sahara Desert. (Photo: Baidu)
From the collected data, scientists have found that the average depth of the Sahara Desert is about 150 meters, equivalent to the height of a 50-story building (assuming each floor is 3 meters), with the deepest point reaching up to 320 meters. This depth is likely the largest for any desert on Earth.
With such a vast and deep desert, the amount of sand is undoubtedly astonishing. So how can we determine what lies beneath the Sahara Desert?
What Lies Beneath the Sahara?
Many people wonder why the sand from the desert is not transported for construction purposes. Unfortunately, desert sand is not like construction sand. The sand in the desert is too fine and smooth, lacking sufficient multi-dimensional chemical bonding. Smaller sand grains may mix easily, but the resulting mortar will be slippery and weaker. Moreover, when the sand is dry, it has better load-bearing capacity, but when wet, the bonds between grains can break, causing the sand to collapse.
Desert sand is too fine and smooth to be used in construction. (Photo: Baidu)
Additionally, the alkali content in desert sand is too high, making it highly reactive with other substances, which can affect the quality of construction. Specifically, the strength and safety of structures cannot be guaranteed, leading to potentially severe consequences.
Furthermore, excavating sand in a vast desert like the Sahara is extremely challenging.
- First, the sheer volume of sand in the Sahara means that excavation would take a significant amount of time.
- Second, moving all the sand from the Sahara is not easy, and finding a place to store it would be difficult. However, hypothetically, if it were possible to excavate all the sand from the Sahara, what would be found underneath?
First, let’s explore the formation of the desert. Geologists have determined that the origin of the sand in the desert has a long and complex history. It is formed from large rocks such as granite, gneiss, and sandstone.
The unique feature of the desert is the temperature difference between day and night. The sudden temperature changes create pressure on the rock formations, causing them to crack. The climate in the desert is extremely arid, and with no vegetation to provide cover, the rocks are increasingly exposed to the elements. Over time, they become ground into finer particles. Some of the products of weathering dissolve, while minerals unaffected by atmospheric agents, such as quartz and insoluble fragments, remain and transform into desert sand.
Below the desert floor lies an unweathered bedrock. (Photo: Baidu)
However, weathering occurs only on the surface of the desert. Below the ground, the weathering diminishes. As a result, when excavating desert sand to greater depths, scientists often encounter sand grains that increase in size. Sometimes, they find not just sand but also numerous rocks and gravel. If excavated deep enough, we may reach the unweathered bedrock, which can sometimes contain valuable mineral deposits. This unweathered rock is referred to as “bedrock.”
Reaching the bedrock can be considered reaching the bottom of the Sahara Desert. However, this answer only addresses the material composition of the Sahara. In reality, the overall terrain of the Sahara Desert contains numerous remnants of rivers and lakes beneath the sand.
This evidence can be observed from satellite images. NASA scientists have created a satellite map of the Sahara Desert using images provided by the Synthetic Aperture Radar (SAR) of the Columbia Space Shuttle. This SAR system is designed to capture images of the Sahara Desert and is capable of penetrating certain surfaces to record images of the Earth’s surface from high altitudes. From the satellite map provided by the Columbia, remnants of a massive ancient lake can be seen beneath the Sahara Desert.
The overall terrain of the Sahara Desert has many remnants of rivers and lakes beneath the sand. (Photo: Baidu)
According to calculations by NASA scientists, the area of this ancient lake reaches 108,000 km2. It is approximately 247 meters deep. Even if it has shrunk, its area still reaches 48,000 km2 and is about 190 meters deep. Additionally, this massive lake is just one of many ancient river and lake beds discovered by the Synthetic Aperture Radar of the Columbia.
This research has also indicated that Sahara is not just a desert.Five to six thousand years ago, the Sahara was a region interspersed with deserts and oases. The Sahara Desert was once a humid area with abundant greenery and animal life. Archaeologists have discovered many dinosaur fossils and even human artifacts within the Sahara Desert.
A group of American scientists from Stony Brook University has published research indicating that the Sahara was home to many marine creatures. The research was based on records from British expeditions in the early 1980s, as well as fossils collected from the Sahara Desert.
Not only rocks, scientists have also found many different fossils in the Sahara Desert. (Photo: Baidu)
According to paleontologist Maureen O’Leary, her team found fossils of catfish and sea snakes in the part of the desert located within Mali. She also noted that 50-100 million years ago, the northern region of Mali was a mangrove forest and a habitat for many mollusk species. At the end of the Cretaceous period and the beginning of the Paleogene, mollusks evolved into giant marine creatures, such as 1.6-meter-long catfish, 12-meter-long sea snakes, and 1.2-meter-long pycnodont fish.
In 1902, archaeologists discovered a 36-million-year-old fossil of a whale located in the Sahara Desert in Egypt. While searching for more fossils in the area, additional whale bones were found in a depression later named Wadi Al-Hitan, which means the Valley of Whales. Scientists believe that intense geological activities over millions of years caused the seabed to rise, transforming this region into the continent we know today.
However, the “oasis period” eventually came to an end. Scientists attribute this change to the axial precession of the Earth. Specifically, the Earth’s axial tilt shifted from 22.1 degrees to 24.5 degrees over a cycle.
Fossils of ancient animals found beneath the sands of the Sahara. (Photo: Baidu)
Axial precession is the slow and gradual change of the Earth in the direction of its rotational axis. This movement is caused by the torque exerted by the Earth and Sun system. It directly affects the tilt at which sunlight strikes the Earth’s surface. The current axial tilt of the Earth is approximately 23.43 degrees.
From this, we can understand that the Earth’s rotational axis does not always point toward the same star (the North Star) but rotates in a clockwise manner, causing the Earth to move similarly to a spinning top. A complete cycle of axial precession takes about 25,700 years.
The axial precession of the Earth will cause periodic changes in the amount of solar energy received by the Sahara Desert and its surrounding areas. Additionally, the summer monsoon winds of the Sahara frequently shift from strong to weak and vice versa. Therefore, when the summer monsoon is stronger, oases in the Sahara have been transformed into dry deserts.
