Geophysical Research Abstracts, Vol. 11, EGU2009-8014-2, 2009 EGU General Assembly 2009 © Author(s) 2009 Permafrost and Periglacial Activity Distribution and Geothermal Anomalies in the Chachani and El Misti Volcanoes (Southern Peru) D. Palacios (1), N. Andrés (2), J. Úbeda (3), and J. Alcalá (4) (1) Dept. AGR y Geografía Física. Universidad Complutense, Madrid, Spain (davidp@ghis.ucm.es), (2) Dept. AGR y Geografía Física. Universidad Complutense, Madrid, Spain (nuriand@ghis.ucm.es), (3) Dept. AGR y Geografía Física. Universidad Complutense, Madrid, Spain (joseubeda@ghis.ucm.es), (4) Dept. AGR y Geografía Física. Universidad Complutense, Madrid, Spain (jalcalar@ghis.ucm.es) The El Misti volcano (16˚17′ S, 71˚24′ W, 5.822 m) is considered one of the most potentially catastrophic in America. Its crater is 18 km from the centre of Arequipa (2335 m a.s.l.), a city with more than 800,000 inhabitants whose population has doubled over the last 20 years, spreading out over the volcano’s sides and gullies in many new settlements, less than 12 km away from the crater. Although the last significant eruptive period occurred in 2300-2050 BP, during the last five thousand years the recurrence period for eruptions has been 500 to 1500 years (Thouret et al. 2001). The last eruption occurred between 1440 and 1447 AD, although it was low-intensity. The crater currently has fumarolic activity. The volcano does not show any signs of having supported glaciers or any periglacial form in the past. The Chachani volcanic complex (16˚11’ S 71˚31’ W, 6.057 m a.s.l.) lies 18 km northeast of El Misti and 22 km from the centre of the city of Arequipa. The complex is made up of several volcanic cones and domes. The date of the most recent eruption is unknown, and no current or recent eruptive activity has been recorded or detected (Paquereau et al. 2006). The complex probably supported glaciers during the Little Ice Age, although there are none at present. Geomorphological evidence shows that glaciers during the Last Glacial Maximum were very extensive, with some of their feet reaching an altitude of 4000m. Rocky glaciers up to 1800 m long can be found inside some of the cirques. The PichuPichi Complex (16º 25’ 25”S 71º14’27”, 5650 m a.s.l.), 22 km E of El Misti, supported substantial glaciers during the Last Glacial Maximum, with a minimum foot altitude of c.4000 m, and like the Chachani, has numerous rock glacier formations in its cirques. The aim of this paper is to ascertain whether the lack of glacial or periglacial geomorphological evidence on the El Misti volcano is due to its destruction from subsequent volcanic activity, or because it never existed. In the latter case, considering its altitude and the conditions in the extinct Chachani and Pichupichu volcanoes nearby, that no evidence is available could be due to the action of geothermal heat, as this is an active volcano. With this aim, three thermal stations were established on El Misti, at altitudes of 4780, 5438 and 5740 m, consisting of an air temperature sensor and a ground temperature sensor, installed at a depth of 20 cm. When possible, a third sensor was installed in the ground at a depth of 40 to 100 cm. Three stations were also installed on the Chachani volcano, at altitudes of 4871, 5013 and 5352 m, with the same orientation where possible, and with the same sensor types and positions. Data was collected during the period 2004-2008. Results obtained for the Chachani volcano during the four complete years for which data is available are fairly uniform, despite the occasional failure of some sensors. For the air temperature, the 0ºC mean annual temperature (MAAT) isotherm is situated at around 5000 m altitude, and the -2ºC isotherm, which we consider the limit of probable permafrost (Palacios et al. 2007), at around 5300 m. At 5352 m, permafrost was not detected at a depth of 40 cm, with 78 days above 0ºC, although it may exist and may be detectable using a deeper probe. The daily temperature range is always very wide, with an average daily range of around 8ºC and a maximum daily range of up to 20ºC. The number of days where the temperature oscillates above and below 0ºC (freeze-thaw cycles) is practically nil at an altitude of 4870 m (between 0 and 75 cycles/year), and maximum at 5013 m (around 200 cycles/year). It then decreases as the altitude increases, with fewer than 150 cycles/year at 5352 m.