In West-Central Africa, a vast body of water stretches across four countries, a vital lifesource for the millions of people living along its shores. But it didn’t always look this way. In fact, thousands of years ago, Lake Chad had a very different appearance – and now NASA has revealed it in all its glory.
Today, Lake Chad covers more than 137 square miles of the continent, its shores stretching across Chad, Cameroon, Niger and Nigeria. But long before the borders of those countries were laid down, it extended over a far bigger area. In fact, these waters once submerged a region almost 3,000 times its current size.
Yes, thousands of years ago, Lake Chad would have been the biggest body of water on planet Earth. But as time passed, its shores retreated, and this vast reserve began to dry up. Today, the parched basin sends atmospheric dust across the Atlantic to South America, sparking a whole new cycle of life.
In fact, the story began more than 40,000 years ago, when this part of the planet was occupied by an inland sea known as Lake Mega Chad. And for many millennia, this vast body of water remained – although it often varied in size. At its deepest, it is believed to have plunged more than 600 feet beneath the surface.
Moreover, when Lake Mega Chad was at its largest, it covered an area of almost 155,000 square miles. For perspective, that would have made it over 10,000 square miles larger than the Caspian Sea. And today, that vast body of water is considered the biggest lake on planet Earth.
So how did this record-breaking lake shrink to such a small fraction of its original size? Well, in June 2015 an article appeared in the journal Proceedings of the National Academy of Sciences. And in it, a team of researchers from a number of institutes based in London, England, revealed some fascinating truths.
Using images captured by satellites above modern-day Chad, Cameroon, Niger and Nigeria, the researchers mapped the shore line of the original lake. Then, they studied samples of sediment taken from the region in order to establish their age. And eventually, they were able to reconstruct the history of this once-vast loch over the past 15,000 years.
According to their research, Lake Mega Chad was at its largest around 6,000 years ago. Back then, experts believe, rainfall in the region initially created the right environment for the body of water to thrive. And through the Mayo Kébbi river in modern day Chad and Cameroon, it seems, the lake connected with the Niger River and, ultimately, the Atlantic Ocean.
Then, around 5,000 years ago, the climate of the region suddenly shifted. And as the level of rainfall dramatically dropped, the landscape of the Sahara began to change. Ultimately, this process would see Lake Mega Chad reduced to a fraction of its former size. However, this would not happen, in the main, for another 4,000 years.
In fact, by the time that the Romans arrived in the region around the first century A.D., Lake Chad was still considered a huge body of water. However, at some point approximately 1,000 years ago, things changed. And over the course of just a few hundred years, the once vast lake dried up almost completely.
Fast forward to the 1960s, and Lake Chad was approximately the same size as North America’s Lake Erie – almost 10,000 square miles. But amazingly, it would shrink further still. You see, people living along the shores of the lake began to siphon too much of its precious water away.
As a result, it’s believed that Lake Chad shrank by as much as 90 percent over the next three decades. Moreover, experts claim that this process has spelled disaster for the countless fishermen and farmers who depend on the water. Suddenly unemployed, they have turned to extremist groups such as Boko Haram, claimed The Guardian.
In fact, the problem has gotten so bad that some activists have been calling on the international community to refill Lake Chad. Apparently, a proposed canal connecting the region with the Democratic Republic of the Congo could help prevent the water levels from dropping any further. But is the project really worth the $50 billion that it is likely to cost?
According to some, it could be a waste of money – given that Lake Chad is not actually shrinking at all. In fact, some critics have pointed to data that suggests the water level has remained steady since the trend was first spotted in the 1990s. Moreover, they claim that proponents of the new canal have taken data out of context and painted an inaccurate picture of the issue.
But whatever the current state of Lake Chad, there is no denying that it is merely a fraction of the size of the great lake that covered much of Africa 6,000 years ago. In any case, far from leaving an ecological disaster, the retreating waters have actually caused life to flourish – albeit thousands of miles away.
You see, the dry depression that was once occupied by Lake Mega Chad is known as the Bodélé depression. At just 500 feet above sea level, it is the lowest spot in the modern-day country of Chad. But while this basin has not contained water for many years, it is the source of another, far stranger, cycle of life.
According to experts, this phenomenon begins when wind from northern Chad’s Ennedi and Tibesti Mountains sweeps down into the Bodélé depression. There, it picks up large amount of diatoms, a type of algae that was left behind when Lake Mega Chad retreated. And soon, the process creates a dust storm that blows through the region as regularly as 100 days a year.
For example, in February 2004 a series of huge dust storms blew out of the Bodélé depression and descended on West Africa. In fact, they even reached the Cape Verde islands, some 350 miles off-shore. However, this is nothing compared to the journey that the winds sometimes make, traveling hundreds of miles across the Atlantic to South America.
In fact, experts have determined that some of these dust storms travel as many as 1,600 miles, eventually arriving at the Amazon rainforest. And there, they play a vital role in keeping this complex and fertile ecosystem alive. Apparently, it’s all down to the nutrients that are present within the diatoms.
Yes, around 30 million tons of nutrient-rich dust makes its way across the Atlantic every year. And among the minerals contained within these currents is phosphorus – a vital component of photosynthesis in plants. Without this, it seems, organisms can not grow properly, resulting in stunted or undeveloped life.
Amazingly, researchers believe that dust storms from the Bodélé depression deposit some 22,000 tons of phosphorus in the Amazon every year. And once there, they help the vegetation of the rainforest grow into the healthy, thick canopy that we see today. But how exactly does this process work?
Between 2007 and 2013, the NASA satellite CALIPSO collected data on nutrients traveling from the Bodélé to the Amazon and beyond. And by February 2015 they had composed a detailed picture covering the journey across the Atlantic. Apparently, an incredible 182 million tons of dust are initially picked up by the wind and carried away from the Sahara.
But by the time that the storms have crossed the Atlantic, some 132 million tons of dust stay in the air while the equivalent of 100,000 truckloads are dumped on the Amazon basin. Eventually, it seems, much of the remaining nutrients make their way out across the Caribbean Sea.
According to NASA, this process represents the largest dust transport system on Earth. But in the Amazon rainforest, it’s not just the arrival of this faraway dust that represents a fascinating miracle. Amazingly, the amount of phosphorus delivered in this fashion – around 22,000 tons – is almost exactly the same as the amount lost through natural processes.
“The Amazon rainforest is like a giant hanging basket,” the University of London at Royal Holloway’s Simon Armitage told the ScienceDaily website in 2015. “In a hanging basket, daily watering quickly washes soluble nutrients out of the soil, and these need to be replaced using fertilizer if the plans are to survive.”
“Similarly, heavy washout of soluble minerals from the Amazon basin means that an external source of nutrients must be maintaining soil fertility. As the world’s most vigorous dust source, the Bodélé depression has often been cited as a likely source of these nutrients,” Dr. Armitage continued. However, if true, this theory presents another strange mystery to researchers.
Apparently, the researchers discovered that, while the climate of Lake Mega Chad shifted 5,000 years ago, the region did not dry up entirely. In fact, experts believe, a small body of water remained in the Bodélé depression until around 1,000 years ago. And while this remaining lake was small, it actually covered the area that produces the most dust today.
Although Dr. Armitage admits that the Bodélé is still the most likely source of the nutrients that fertilize the Amazon, he questions how long this could have been the case. “Our findings indicate that this can only be true for the last 1,000 years,” he explained. So how did the rainforest grow before dust storms began blowing phosphorus and more across the Atlantic?
According to most estimates, the Amazon rainforest has been in existence for some 55 million years. And currently it’s unclear as to how its vegetation thrived for so long without the assistance of the Bodélé depression’s dust storms. So far, this puzzle has yet to be solved.
Fast forward six years, however, and another project has shed a fascinating light on the history of Lake Mega Chad. On February 17, 2020, NASA released the latest in their Image of the Day series. A popular feature on the space agency’s website, this initiative features a different snapshot from their archives each day of the year.
And this time, NASA’s Image of the Day was a stunning picture of Lake Chad from above. But the highlight wasn’t the chance to view one of Africa’s biggest bodies of water from a whole new angle. Instead, the photograph offered a fascinating glimpse into the region’s distant past.
Back in February 2000, NASA joined forces with America’s National Imagery and Mapping Agency, which would later become the National Geospatial Intelligence Agency, or NGA. And together, these institutions launched the Shuttle Radar Topography Mission, or SRTM. Using radar technology, the two groups embarked on an ambitious project to map the surface of planet Earth.
For 11 days, the Space Shuttle Endeavour collected data on the topography of the Earth. And eventually, it succeeded in mapping the elevation levels of around 80 percent of our planet. In fact, it became the most complete set of data of its kind ever made. Afterwards, the NGA used this information to fine-tune everything from navigational tools to environmental ideas.
However, the data collected by SRTM had another purpose. Using the mission’s observations, experts at NASA were also able to build up a clearer picture of how the land surrounding Lake Chad once looked. And once they combined it with a satellite image of the area, the resulting photograph brought the region’s fascinating story to life.
On February 11, 2013, NASA launched the Landsat Data Continuity Mission, now known as Landsat 8. And since then, the satellite has been capturing high resolution images of the Earth from above. In fact, its stint in space represents the most comprehensive record of the surface of our planet ever collected from above.
According to NASA, one of the pieces of technology on Landsat 8 is the Operational Land Imager, or OLI. Using multi-spectral technology, this system is able to capture high-resolution photographs of the planet below. Amazingly, the result is so detailed that it can pick out individual features such as forests and farms.
So by combining data from SRTM and OLI, researchers at NASA were able to create a stunning image of Lake Chad from above. In it, the spot occupied by the modern lake can clearly be seen in the south western corner of the Bodélé depression. However, this speck of water makes up merely a tiny fraction of a vast and fascinating landscape.
In the aerial image, the data from SRTM also reveals a large area of low elevation stretching for hundreds of miles beyond the shoreline of the modern lake. And according to experts, this vast mass represents the region once covered by Lake Mega Chad. Moreover, the photograph also highlights specific geological features, such as ridges and sand spits, that once formed at the water’s edge.
Apparently, these sand spits and ridges are typically formed in inlets such as estuaries and coves. As winds deposit sand across these regions, experts believe, they build up to create these distinctive features. And in the case of Lake Mega Chad, it seems, prevailing northeast winds caused these elevations to develop in a southwesterly direction.
As the climate of planet Earth continues to change, large bodies of water such as Lake Chad face an even more uncertain future. But by studying how their surfaces have fluctuated over the years, we might be able to learn more about the complex processes that affect our planet. And armed with this data, it is hoped, we might be able to prepare ourselves for what’s to come.