How an Ancient Society in the Sahara Desert Rose and Fell with Groundwater
Pittsburgh, Pa., USA: With its low quantities of rain and soaring high
temperatures, the Sahara Desert is often regarded as one of the most
extreme and least habitable environments on Earth. While the Sahara was
periodically much greener in the distant past, an ancient society living in
a climate very similar to today’s found a way to harvest water in the
seemingly dry Sahara—thriving until the water ran out.
New research that will be presented Monday, 16 Oct., at the Geological
Society of America’s GSA Connects 2023 meeting describes how a series of
serendipitous environmental factors allowed an ancient Saharan
civilization, the Garamantian Empire, to extract groundwater hidden in the
subsurface, sustaining the society for nearly a millennia until the water
was depleted.
“Societies rise and fall at the pleasure of the physical system, such that
there are special features that let humanity grow up there,” says Frank
Schwartz, professor in the School of Earth Sciences at The Ohio State
University and lead author of the research study.
Monsoon rains had transformed the Sahara into a comparatively lush
environment between 11,000 and 5,000 years ago, providing surface water
resources and habitable environments for civilizations to thrive. When the
monsoon rains stopped 5,000 years ago, the Sahara turned back into a
desert, and civilizations retreated from the area—aside from an unusual
outlier.
The Garamantes lived in the southwestern Libyan desert from 400 BCE to 400
CE under nearly the same hyper-arid conditions that exist there today and
were the first urbanized society to become established in a desert that
lacked a continuously flowing river. The surface water lakes and rivers of
the “Green Sahara'' times were long gone by the time the Garamantes
arrived, but there was luckily water stored underground in a large
sandstone aquifer—potentially one of the largest aquifers in the world,
according to Schwartz.
Camel trade routes from Persia through the Sahara brought the Garamantes
technology on how to harvest groundwater using foggara or
qanats. This method involved digging a slightly inclined tunnel into a hillside,
to just below the water table. Groundwater would then flow down the tunnel
and into irrigation systems. The Garamantes dug a total of 750 km of
underground tunnels and vertical access shafts to harvest groundwater, with
the greatest construction activity occurring between 100 BCE and 100 CE.
Schwartz integrates prior archaeological research with hydrologic analyses
to understand how the local topography, geology, and unique runoff and
recharge conditions produced the ideal hydrogeologic conditions for the
Garamantes to be able to extract groundwater.
“Their qanats shouldn’t have actually worked, because the ones in
Persia have annual water recharge from snowmelt, and there was zero
recharge here,” says Schwartz.
The Garamantes had a significant streak of environmental luck, with the
earlier wetter climate, appropriate topography, and unique groundwater
settings, which made groundwater available with foggara technology.
However, their luck ran out when groundwater levels fell below the
foggara
tunnels.
According to Schwartz, two trends are particularly concerning. First,
extreme environments are becoming more prevalent around the world in
countries like Iran. Second, it has become more common to use groundwater
unsustainably.
“As you look at modern examples like the San Joaquin Valley, people are
using the groundwater up at a faster rate than it’s being replenished,”
says Schwartz. “California had a great wet winter this year, but that
followed 20 years of drought. If the propensity for drier years continues,
California will ultimately run into the same problem as the Garamantians.
It can be expensive and ultimately impractical to replace depleted
groundwater supplies.”
With no new water to replenish the aquifer and no surface water available,
lack of water led to the downfall of the Garamantian Empire. The Garamantes
serve as a cautionary tale for the power of groundwater as a resource, and
the danger of its overuse.
Living in Extreme Environments: Hydrologic Serendipity and the
Garamantian Empire of the Sahara Desert
Contact: Frank Schwartz, schwartz.11@osu.edu
87: T142. Achieving Groundwater Security across Local-to-Regional Scales in the Anthropocene
Mon., 16 Oct. 2023, 8:05–8:25 a.m.
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