Creeping permafrost in Mexico: environmental status of "Nevado" Rock Glacier, Nevado de Toluca volcano

In contrast to glaciological studies in Mexico, periglacial studies are very recent and limited to the analysis of the general permafrost cover in the high mountains of the country. Although some of the studies on the reconstruction of Pleistocene glaciers in Mexico mention the existence of rock glaciers, to date no work has been done to study their physical properties or determining their state of conservation. Since rock glaciers are the most important visible indicators of mountain permafrost (along with features such as gelifluction lobes and patterned ground) and given that the "Nevado" rock glacier is the main example of its kind in Mexico, this study analyzes its internal temperature and assesses its state of conservation. The investigation was carried out by drilling and thermal monitoring of rock profiles as well as air. The results indicate that at present, the "Nevado" seems to lack permafrost inside. Although there is evidence of surface freezing during the winter months in the upper part of the rock glacier, in the lower portion it is almost unnoticed; and in both parts the internal temperature shows a tendency towards positive values as depth increases, a situation that predominates throughout the year. In addition, according to the records of the climatological station located in the lower part of the rock glacier, although the annual rainfall regime could be favorable for the formation and feeding of interstitial or segregated ice, the air temperature conditions throughout the year prevent permanent freezing. The sum of the above determines that at present the "Nevado" could be considered as an inactive and relict-type rock glacier; the presence of vegetation on the surface of the debris that make it up corroborates its inactivity.