466
Climatic Geomorphology
This gives rise to the risk of subsidence, which can have important socio-economic
consequences (Guti6rrez and Pefia, 1994). The alluvial deposits overlaying the evaporitic
formations, which can be over 100 m thick, have been explained by sedimentary
karstic subsidence (see Guti6rrez and Guti6rrez, 1998). The alluvial cover subsides
because of ductile flexure or fragile collapse.
Around Zaragoza, Spain, subsidence affects roads (Figs 19.5 and 19.6) and railways
(Benito and Guti6rrez, 1988; P6rez del Campo, 1989; Benito and P6rez del Campo, 1991;
Benito et al., 1995), houses, warehouses and even the water supply to the west of the city
(Casetas-Utebo) (Zuidam, 1976a,b; Guti6rrez et al., 1985; Soriano et al., 1994; Soriano
and Sim6n, 1995; Guti6rrez and Guti6rrez, 1998). The most spectacular case, however, is
that of the new town of Puilatos (about 30 km north of Zaragoza), whose construction had
to be abandoned. What had been built had to be destroyed because of the numerous cracks
caused by subsidence through karstification (Benito and Guti6rrez, 1988).
The area's lined irrigation network has also suffered the effects of subsidence. In 1954,
the La Violada concrete canal gave way because of a collapsed doline 25 m in diameter
(Llamas, 1962; Riba and Llamas, 1962). Non-lined canals, such as the Canal Imperial de
Arag6n, supplied water to the underlying gypsum, starting a karstification process and
the generation of dolines. A relationship exists between the density of dolines and their
proximity to irrigation ditches in the area of Villamayor in Zaragoza. The highest
concentration of dolines is close to the irrigation ditches, especially at their confluence
(Fig. 19.7) (Benito and Guti6rrez, 1988), showing that water leakage from the ditches
is the main cause of dissolution in the area and therefore of the ensuing subsidence.
Figure 19.5. Flexure between the Pikolin factory and the Zaragoza-Arag6n highway in Spain caused by
karstic subsidence of the underlying gypsum (June, 1996). Photo: F. Guti6rrez.
Climatic Geomorphology
This gives rise to the risk of subsidence, which can have important socio-economic
consequences (Guti6rrez and Pefia, 1994). The alluvial deposits overlaying the evaporitic
formations, which can be over 100 m thick, have been explained by sedimentary
karstic subsidence (see Guti6rrez and Guti6rrez, 1998). The alluvial cover subsides
because of ductile flexure or fragile collapse.
Around Zaragoza, Spain, subsidence affects roads (Figs 19.5 and 19.6) and railways
(Benito and Guti6rrez, 1988; P6rez del Campo, 1989; Benito and P6rez del Campo, 1991;
Benito et al., 1995), houses, warehouses and even the water supply to the west of the city
(Casetas-Utebo) (Zuidam, 1976a,b; Guti6rrez et al., 1985; Soriano et al., 1994; Soriano
and Sim6n, 1995; Guti6rrez and Guti6rrez, 1998). The most spectacular case, however, is
that of the new town of Puilatos (about 30 km north of Zaragoza), whose construction had
to be abandoned. What had been built had to be destroyed because of the numerous cracks
caused by subsidence through karstification (Benito and Guti6rrez, 1988).
The area's lined irrigation network has also suffered the effects of subsidence. In 1954,
the La Violada concrete canal gave way because of a collapsed doline 25 m in diameter
(Llamas, 1962; Riba and Llamas, 1962). Non-lined canals, such as the Canal Imperial de
Arag6n, supplied water to the underlying gypsum, starting a karstification process and
the generation of dolines. A relationship exists between the density of dolines and their
proximity to irrigation ditches in the area of Villamayor in Zaragoza. The highest
concentration of dolines is close to the irrigation ditches, especially at their confluence
(Fig. 19.7) (Benito and Guti6rrez, 1988), showing that water leakage from the ditches
is the main cause of dissolution in the area and therefore of the ensuing subsidence.
Figure 19.5. Flexure between the Pikolin factory and the Zaragoza-Arag6n highway in Spain caused by
karstic subsidence of the underlying gypsum (June, 1996). Photo: F. Guti6rrez.