Evidence of glacial activity during the Oldest Dryas in the mountains of Spain

Abstract

Abstract In this review, recently published results of cosmogenic dating of moraine boulders, rock glaciers and glacially-polished surfaces in various mountain massifs (the Sierra Nevada, the Central Range, the Pyrenees and the Northwestern Mountains) of the Iberian Peninsula were analysed to assess the importance of the glacial advance and subsequent retreat that occurred during the Oldest Dryas, between 17.5 and 14.5 ka. The glaciers, which had almost disappeared at the beginning of this period (approximately 17.5 ka), returned to fill the valley floors at approximately 16.8–16.5 ka, depositing moraines close to the moraines generated during the Last Glacial Maximum advance. Following this intense and short advance, the glaciers began to retreat, although this was frequently interrupted by glacial readvance episodes, with the last occurring at approximately 15.5 ka. Subsequently, the retreat was generalized, so that 1 ka later the glaciers were restricted to the cirque areas, and never again advanced. During this recession, the activity of many of the deglaciated cirque walls triggered frequent rockfalls, transforming the retreating degraded glaciers into rock glaciers; their fronts had become inactive by approximately 14 ka, although in many cases their roots conserved the internal ice until well into the Holocene. The glacial fluctuations, and the landforms and deposits consequently derived from them, are very similar to those described for other Mediterranean and European mountain ranges, especially the Alps. We conclude that the climate changes associated with the Oldest Dryas, had important impacts on mountain landscapes throughout the continent.