25 / 80
plains, and salt flats, with large sand
dunes forming only a minor part.
The topography ranges from the
Tibesti Massif of northern Chad (at
11,000 feet/3350 meters) to the
Qattara Depression of Egypt (at 436
feet/133 meters). Scattered, fertile
oases usually lie in depressions,
punctuating the ancient caravan
routes which, over time, have been
adapted into modern roads. Here,
water is present where the water
table comes to the surface, and at
greater depths lies in huge
underground aquifers. These are
believed to be filled with water
dating from the Pleistocene period,
when the Sahara was much wetter
than it is today; the more than 20
lakes or
chotts
in the north, and the
areas of salt flats and boggy salt
marshes, are also thought to be
remnants of this pluvial age.
We know that rivers once ran
through the Sahara, because dried-
up riverbeds, known as
wadis
, still
exist, which fill up with water and
become active streams for a short
time. The Nile and the Niger are
the only permanent rivers in the
region, being fed by rainfall outside
the area.
A Concise History of Africa
Natural Resources
Important discoveries of
minerals, oil, and gas
have been made in the Sahara,
but in most cases inaccessibility
has delayed their exploitation.
Salt is still mined, as in the past,
at Taoudenni in Mali, and at
Bilma in Niger, and it is
transported, as in the days of
the great medieval kingdoms of
West Africa, by camel caravans
across the desert.
25