386
Climatic Geomorphology
Figure 16.5. Large halite accumulations in the central areas of the littoral sebkha, E1 Melah, Zarzis,
Tunisia.
Glennie (1970) distinguished between interior and littoral sebkhas (Figure 16.5). The
latter are saline plains located in littoral arid areas, affected by marine water penetration
and with tidal-related deposits. High-soluble salts are commonly precipitated in these
littoral sebkhas because they are located in areas with high evaporation rates. Some
modern examples occur in the Persian Gulf and south of Tunisia.
Most of the closed desert depressions are small. The largest one is the Salar de Uyuni
located in the Bolivian Altiplano at 3653 m a.s.1 (Figure 10.9 and Figure 16.6) with a
surface area up to 9000 kin 2 (Rettig et al., 1980). During the Pleistocene period, the Salar
was a lake (Minchin Lake) that reached more than 43,000 kin 2 (Blair, 1986). Lacustrine
depressions represent less than 1% of the total desert area (Shaw and Thomas, 1997),
although in some regions of South Africa they cover up to 20% of the surface (Goudie
and Wells, 1995). In NW Texas there are between 30,000 and 37,000 lacustrine basins
(Osterkamp and Wood, 1987). With only the exception of tectonic lakes, most basins
located in arid zones do not exceed 15 m water depth at the maximum lake level (Mabbutt,
1977). Tectonic lakes are commonly elongated, parallel to the regional tectonic faults and
structures. Deflation, or wind-erosion, can also originate elongated lakes following the
direction of the prevalent winds. In most cases, however, closed desert depressions are
approximately circular in shape. If water and sediment input is low, the bottom of the lake
is usually irregular. With increasing clastic deposition, small topographic bottom
irregularities disappear. Waves, currents, and other dynamic agents produce bars, barrier
islands, spits, and other geomorphic features in the saline lakes, as in the Laguna de
Gallocanta in Zaragoza and Teruel provinces in Spain (Figure 16.7, Gracia, 1995).
Climatic Geomorphology
Figure 16.5. Large halite accumulations in the central areas of the littoral sebkha, E1 Melah, Zarzis,
Tunisia.
Glennie (1970) distinguished between interior and littoral sebkhas (Figure 16.5). The
latter are saline plains located in littoral arid areas, affected by marine water penetration
and with tidal-related deposits. High-soluble salts are commonly precipitated in these
littoral sebkhas because they are located in areas with high evaporation rates. Some
modern examples occur in the Persian Gulf and south of Tunisia.
Most of the closed desert depressions are small. The largest one is the Salar de Uyuni
located in the Bolivian Altiplano at 3653 m a.s.1 (Figure 10.9 and Figure 16.6) with a
surface area up to 9000 kin 2 (Rettig et al., 1980). During the Pleistocene period, the Salar
was a lake (Minchin Lake) that reached more than 43,000 kin 2 (Blair, 1986). Lacustrine
depressions represent less than 1% of the total desert area (Shaw and Thomas, 1997),
although in some regions of South Africa they cover up to 20% of the surface (Goudie
and Wells, 1995). In NW Texas there are between 30,000 and 37,000 lacustrine basins
(Osterkamp and Wood, 1987). With only the exception of tectonic lakes, most basins
located in arid zones do not exceed 15 m water depth at the maximum lake level (Mabbutt,
1977). Tectonic lakes are commonly elongated, parallel to the regional tectonic faults and
structures. Deflation, or wind-erosion, can also originate elongated lakes following the
direction of the prevalent winds. In most cases, however, closed desert depressions are
approximately circular in shape. If water and sediment input is low, the bottom of the lake
is usually irregular. With increasing clastic deposition, small topographic bottom
irregularities disappear. Waves, currents, and other dynamic agents produce bars, barrier
islands, spits, and other geomorphic features in the saline lakes, as in the Laguna de
Gallocanta in Zaragoza and Teruel provinces in Spain (Figure 16.7, Gracia, 1995).