SURGE GLACIERS DURING THE LITTLE ICE AGE IN THE PYRENEES

Historical moraine complexes and erosional features are interesting elements to discern the historical climate changes and evolution, with a complex chronologies that help us to understand the dynamics and glacier evolution during the Little Ice Age (LIA). The existence of landforms as crevasses-squeeze ridges, hummocky moraines and flutes, related to different glacier advances and retreats, allows understanding in a better way the LIA glacier evolution in the Pyrenees. The aim of this work is to show how many LIA moraine complexes have traces of fast flow ice; when the surge dynamic happened; his extent and the environmental meaning. Based on glacier landsystem analysis we have established a work hypothesis on the fast flow or surge dynamic glaciers during the LIA, with geomorphological features, as flutes and push and hummocky moraines, at least in 17 LIA glacier complexes. The analysis of morphosquences by fieldwork, photo interpretation and historical sources in 8 selected LIA moraine complexes have been compared with previous climatic reconstructions creating a hypothesis about the response of the LIA glaciers to the short time changes in temperature and moisture. The glacier cirques with fast flow features are found in the highest mountains with summits above 3000 m., mainly northern oriented (88%) and without a significant lithology. The studied complexes (Central Infierno, Eastern Infierno, Oulettes de Gaube, Monte Perdido, Marbore, La Paul, Literola and Tempestades) show 4 morphological units: a frontal moraine system (U1); a more voluminous moraine (U2); a little push and hummocky moraines complex linking with flutes (U3); and minor arcs up valley (U4). The U3 belongs to a fast flow stage or surging and by morphostratigraphy we can point out that the surge processes were produced between 1820 and 1840, at the end of the LIA. We related it with a possible climatic response to sudden cooling and the increase of winter precipitation with melt-water availability and quick ice melting during the summer, generating hydrodynamic changes in the small glaciers and quick dynamic response.