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Abstract:
This paper reviews the current knowledge of the mainly karstic geomorphological features developed in the evaporitic formations of the Ebro Depression (northern Spain). Special emphasis is given to the recently published and unpublished scientific advances. The gypsum formations, of Tertiary age, have an extensive outcrop area within the Ebro Depression. Here, their morphogenesis is controlled mainly by processes of surface and subsurface dissolution acting on the gypsum. Outstanding landforms in the gypsum terrain include saline lakes developed in flat bottom dolines (saladas). Other characteristic morphologies include karren and gypsum domes, which occur on a decimetre scale. Where the gypsum is covered by Quaternary alluvial deposits the karstification processes are especially intense and cause subsidence phenomena. Karstic subsidence affects stream terraces, mantled pediments and infilled valleys, which in the region are called vales. Dissolution-induced synsedimentary subsidence has produced interesting geological features, which include significant thickening and deformation of the alluvial deposits. In contrast to the rapid removal of gypsum by dissolution, the amount of gypsum removed by erosion is low. Water erosion studies carried out on gypsiferous slopes of the Ebro Depression, indicate that the sediment yield ranges from 0.59 to 7.82 t/ha/year. This low yield results from the high infiltration capacity of the soils. Subsidence caused by gypsum dissolution has important socioeconomic consequences in the Ebro Depression. The active alluvial karstification of the gypsum causes numerous sinkholes that are harmful to linear structures (roads, railway Lines, irrigation channels), buildings and agricultural land. Unforeseen catastrophic subsidence also puts human Lives at risk. The benefits of such terrains include thickened alluvial deposits which act as valuable water reservoirs and which form excellent sources of aggregates. Fluvial valleys in this gypsiferous terrain commonly show an asymmetrical geometry with prominent gypsum scarps at one side. These gypsum scarps are affected by numerous landslides. These slope movements are hazardous, may dam rivers and cause flooding of the alluvial plains. (C) 1998 Elsevier Science B.V. All rights reserved