A slow-motion disaster
On the Muela de Cortes, a limestone plateau in Valencia, a vast section of a mountain is sliding into the gorge of the Júcar River. This is not a sudden, catastrophic event, but a slow, relentless creep. The mass of rock and earth, with an estimated volume of hundreds of millions of cubic meters, is a deep-seated gravitational slope deformation. Its average speed is just two centimeters per year, a rate of movement almost imperceptible to the naked eye.
The landslide is occurring in a region of complex geology at the confluence of the Iberian and Betic mountain ranges. The plateau itself is composed of Cretaceous-era marine limestones and marls. This type of layered sedimentary rock, when undercut by river erosion and saturated with water, can become highly unstable. The Júcar River has carved a deep canyon at the base of the Muela, creating steep slopes that are primed for failure. The movement is not uniform; different parts of the mass move at different rates, and the entire slide accelerates in response to specific weather events.
Watched from space
Scientists monitor the Muela de Cortes landslide using a satellite-based technique called Interferometric Synthetic Aperture Radar (InSAR). By comparing high-resolution radar images taken at different times, InSAR can detect minute changes in the ground surface with millimeter-level accuracy. This technology allows for continuous observation over a wide area without the need for ground-based equipment in a dangerous and difficult-to-access location.
The data from InSAR has revealed a direct and critical relationship between rainfall and the landslide's speed. Following periods of heavy rain, particularly in the autumn, the rate of movement can more than double. The water percolates through the porous limestone, increasing the pore water pressure within the rock mass. This pressure effectively lubricates the potential failure planes deep within the slope, reducing friction and allowing the massive block to slide more easily under the force of gravity. The monitoring provides a detailed picture of how the slope destabilizes, showing the mechanics of such large-scale movements.
Eventually, the slope will collapse. Eventually, the sliding mass will fail completely and slump into the Júcar River gorge. Such an event would create a massive natural dam, blocking the river's flow and creating a large lake behind it. This would inundate the valley upstream and pose a severe flood risk to communities downstream should the natural dam suddenly breach. The Júcar river basin is already an area of flood risk, making the potential collapse of the Muela de Cortes a major long-term hazard for the region.