LIVING IN EXTREME ENVIRONMENTS: HYDROLOGIC SERENDIPITY AND THE GARAMANTIAN EMPIRE OF THE SAHARA DESERT (Invited Presentation)

Places exist on planet Earth that have historically been uninhabitable because of extreme dryness and an apparent absence of available water. Yet, in the midst of extreme desert settings hydrologic serendipity sometimes provided unique settings capable of providing a livable environment for human societies at least for a while. Here, we examine how serendipity played a role in moderating the impacts of hyper-arid conditions. Within our study area in S.W. Libya, archaeological evidence pointed to human habitation not only during the Green-Saharan times of Early and Middle Holocene (12,000-5,000 years BP), but also in the Late Holocene with the Garamantian Empire (400 BCE to 400 CE), which featured towns and larger settlements. The ascendancy of the Garamantian empire was remarkable given a climate comparable to the modern-day Libyan Sahara Desert.

The Garamantians lived along Wadi el-Agial at the base of the large escarpment formed by sandstones of Messak Settafet massif. Their empire developed around a novel tunnel-based system for extracting groundwater from alluvial fans and moving to valleys below. This foggara or qanat technology was developed in Persia about 2,500 BP and spread rapidly along trade routes. More than 500 foggaras ranging in length from 100 m to 4.5 km were dug by hand to irrigate crops. What is surprising is that they produced water at all. Hydraulically, qanats of Persia typically tapped annual recharge to unconfined alluvial aquifers containing small volumes of stored water. In the case of the Garamantians, however, humid conditions of Green-Saharan times were long gone with foggaras removing stored water to the point of exhaustion. We suspect the foggaras functioned only because of the unique hydrogeologic features that came together there. Alluvial sediments at the base of Messak escarpment in which the foggaras were placed were part of a regional topographic flow system, which moved water from the large sandstone aquifer systems of the Messak Formation to discharge areas in Wadi el-Agial. The topography of the bedrock surface exposed across the Messak focused runoff to localized areas of sands and gravels conducive to recharge. Thus, even limited rainfall of the Early and Middle Holocene was able to recharge the aquifer system.