Ancient lakes of the Sahara

The Sahara has not always been the arid, inhospitable place that it is today – it was once a savannah teeming with life, according to researchers at the Universities of Reading and Leicester.

Eight years of studies in the Libyan desert area of Fazzan, now one of the harshest, most inaccessible spots on Earth, have revealed swings in its climate that have caused considerably wetter periods, lasting for thousands of years, when the desert turned to savannah and lakes provided water for people and animals.

This, in turn, has given us vital clues about the history of humans in the area and how these ancient inhabitants coped with climate change as the land began to dry up around them again.

In their article ‘Ancient lakes of the Sahara’, which appears in the January-February issue of American Scientist magazine, Dr Kevin White of the University of Reading and Professor David Mattingly of the University of Leicester explain how they used satellite technology and archaeological evidence to reveal new clues about both the past environment of the Sahara and of human prehistory in the area.

“The climate of the Sahara has been highly variable over the millennia and we have been able to provide much more specific dating of these changes,” said Dr White. “Over the last 10,000 years, there have been two distinct humid phases, separated by an interval of highly variable but generally drying conditions between roughly 8,000 and 7,000 years ago. Another drying trend took place after about 5,000 years ago, leading to today’s parched environment.”

The researchers determined where surface water was once present by using radar images of the desert taken from space. These images showed rivers, lakes and springs now buried below shifting sand dunes. As these bodies dried out thousands of years ago, the resulting mineral deposits cemented the lake sediments together and these hardened layers are detectable by using radar images.

“This information was essential because archaeologists need to focus their efforts near ancient rivers, lakes and springs, where people used to congregate due to their basic need for water,” said Dr White. “We found large quantities of stone tools around the ancient water sources, indicating at least two separate phases of human occupation.”

The earliest humans in the area were Palaeolithic hunter-gatherers, who lived in the Fazzan between about 400,000 and 70,000 years ago. They survived by hunting large and small game in a landscape that was considerably wetter and greener than it is now. A prolonged arid phase from about 70,000 to 12,000 years ago apparently drove humans out of the region, but then the rains returned – along with the people.

Around 5,000 years ago the climate began to dry out again, but this time people adapted by developing an agricultural civilization with towns and villages based around oases. This process culminated with the emergence of the Garamantian society in the first millennium BC.

Professor Mattingly said: “We have been given a completely new view of this elusive and remarkable society. The Garamantes were known to the ancient Romans as a race of desert warriors, but archaeology has shown they had agriculture, cities and a phenomenally advanced system of water extraction that kept their civilisation going for 1,000 years as the land was drying up around them.”

They cultivated a variety of high-grade cereals, such as wheat and barley, and other crops such as date palms, vines, olives, cotton, vegetables and pulses.

As the Saharan climate began to dry out they drew their water from a large subterranean aquifer (an underground bed of rock that yields water) and transported it through a network of tunnels.

“The fact that the Garamantes developed this ingenious irrigation system shows that our ability to apply engineering solutions to deal with climate change is by no means only a modern phenomenon,” said Dr White. “The gradual drying up of springs and dessication of the surrounding landscape must have seemed ominous , but they knew they had to develop sophisticated methods to cope with it.

“But even this remarkably adaptable society – one of the first urban civilisations built in a desert – could not cope forever with a falling water table and intensifying aridity. Sometime around 500AD, the Garamantian society collapsed and their irrigation system fell into disuse.”

Associated with this research, Reading’s School of Human and Environmental Sciences, in collaboration with the Department of Meteorology, are undertaking a major project, linking climate, water and civilization in the Middle East and North Africa, with a £1,240,000 grant from the Leverhulme Trust.