A research team from the University of the Basque Country-EHU has determined that river erosion is the main reason for uneven lifting of the Earth's crust across the Basque-Cantabrian Range. This mountain range, located in northern Spain, stretches from Castro Valnera, near the borders of Burgos and Cantabria, all the way to the Pyrenees. The study found that the Atlantic side of the range has risen by 255 meters (837 feet), while the Mediterranean side has risen by 167 meters (548 feet), creating an 88-meter difference in elevation. This is the first study to quantify this difference in uplift across the two sides of the range. The researchers used a combination of traditional and modern methods to analyze the erosion in 35 river basins covering an area of 13,190 square kilometers. They found that the Atlantic slope has experienced more erosion, with 2,019 cubic kilometers of rock removed compared to 1,408 cubic kilometers on the Mediterranean side. This greater erosion has led to more isostatic uplift on the Atlantic slope. Isostatic adjustment is a geological process where the Earth's crust rises in response to the removal of weight, similar to how a boat floats higher in water when a heavy load is removed. Iván Martín Martín, a researcher at the University of the Basque Country-EHU, explained that as erosion removes material from the surface, the crust adjusts by rising to maintain balance. The Atlantic slope has a more developed river network, with shorter rivers, steeper gradients, and higher rainfall, contributing to the increased erosion. The study also notes that the uplift has not been purely vertical but has caused a slight westward tilt, particularly noticeable in the central region that includes cities like Bilbao and Vitoria-Gasteiz. The research also highlights the impact of the Messinian salinity crisis, a significant geological event around 6 million years ago that led to dramatic changes in the Mediterranean Sea, including periods of extreme dryness and erosion. This event may have contributed to the differences in erosion and uplift between the two sides of the Basque-Cantabrian Range. The findings provide important insights into how rivers form, how landscapes evolve, and the factors that contribute to the differences in elevation between the Atlantic and Mediterranean sides of the range.