The deglaciation of the Sierra Nevada (Southern Spain)

Cosmogenic 36Cl surface exposure dating was carried out on 19 samples from glacially polished bedrock, rock glaciers and moraines of four glaciated valleys with different orientations in the Sierra Nevada (Spain) around Pico del Veleta (37° 3′N 3° 21′W, 3398 m asl). Remains of moraines older than the global Last Glacial Maximum exist, but their poor preservation makes them an unreliable subject for surface exposure dating. Results show that the last local glacial maximum advance took place earlier than the global Last Glacial Maximum, but within the MIS 2, although additional dating is needed to confirm this. Exposure ages from bedrock steps show a general glacier retreat in progress by 15–14 ka. Shortly afterwards an extensive system of rock glaciers formed at the base of the valley headwalls, with the most recent rock glacier lasting until 7 ka ago. From their location, morphology and analysis of other proxies, we interpret their origin as related to the deglaciation process and marked instability of cirque headwalls, rather than to extreme periglacial conditions. A recent similar occurrence was the transformation of the Little Ice Age glacier on the north face of the Pico del Veleta into a rock glacier under temperate high mountain climatic conditions.