Subsidence Hazards due to Evaporite Dissolution in the Huerva Valley (NE Spain)

The last 17 km-long reach of the Huerva River valley, up to its confluence with the Ebro River in Zaragoza city, flows through salt-bearing evaporites of the Ebro Tertiary Basin (NE Spain). The alluvium overlying evaporite bedrock shows spectacular paleosinkholes and soft sediment deformations interpreted as liquefaction structures resulting from ground acceleration induced by catastrophic subsidence. In the lower most reach of the valley, where the substratum has a higher solubility, terrace deposits thicken over 60 m. Subsidence affects both the alluvium and the underlying bedrock indicating that dissolution acts at the rockhead beneath the alluvial cover (alluvial karst) and within the evaporitic substratum (interstratal karst). The intra-evaporitic karst seems to be due to salt dissolution. Numerous buildings in Cadrete and Santa Fe villages have been severely damaged by subsidence. Several linear infrastructures like the Imperial Channel and an almost completed high-speed railway are affected by human-induced sinkholes. The paleocollapse structures exposed in the trenches of this railway and a ring-road under construction point to hazardous locations underlain by cavities, where special prevention measures should be applied.