For Peer Review Monitoring permafrost and periglacial processes in Sierra Nevada (Spain) from 2001 to 2016 Journal: Permafrost and Periglacial Processes Manuscript ID PPP-19-0002.R2 Wiley - Manuscript type: Special Issue Paper Date Submitted by the Author: n/a Complete List of Authors: Ortiz, Antonio; University of Barcelona Oliva, Marc; University of Barcelona, Department of Geography Salvador-Franch, Ferran; University of Barcelona, Department of Geography Palacios, David; University Complutense, Department of Geography Tanarro, Luis Miguel; Universidad Complutense de Madrid, Geografia Sanjosé Blasco, Jose Juan; Universidad de Extremadura, Departmento de Expresión Gráfica Salvà-Catarineu , Montserrat; University of Barcelona Keywords: Sierra Nevada, Little Ice Age, periglacial processes, permafrost, seasonal frozen ground http://mc.manuscriptcentral.com/ppp Permafrost and Periglacial Processes For Peer Review 1 Abstract 2 Outside the Alps, Sierra Nevada is probably the best studied European massif with respect to its past and 3 current environmental dynamics. A multi-approach research program started in the early 2000s focused on the 4 monitoring of frozen ground conditions in this National Park. Here, we present data on the thermal state and 5 distribution of permafrost and seasonal frozen ground in different sites across the highest lands of the massif. 6 New results confirm the absence of widespread permafrost conditions, with seasonal frost prevailing above 7 2500 m. Small permafrost patches have been only detected in glaciated areas of the Veleta and Mulhacén 8 cirques during the Little Ice Age at elevations of 3000-3100 m. The remnants of those glaciers are still 9 preserved under the thick debris layer covering the cirque floors. Geomatic and geophysical surveying of a 10 rock glacier existing in the Veleta cirque, together with the monitoring of soil temperature at different depths, 11 have revealed permanently frozen conditions undergoing a process of degradation. In the rest of the massif, 12 seasonal frost regime prevails, even at the highest plateaus at 3300-3400 m, where annual soil temperatures 13 average 2.5 ºC. The monitoring of soil temperatures in other different periglacial features has also reported 14 positive average values ranging between 2ºC (inactive sorted-circles) and 3-4ºC (inactive and weakly active 15 solifluction lobes). Consequently, we conclude that the present-day climatic regime does not allow the 16 existence of permafrost in Sierra Nevada, and environmental dynamics is controlled by the intensity and 17 duration of seasonal frost in the ground. 18 19 Key words: Sierra Nevada, Little Ice Age, periglacial processes, permafrost, seasonal frozen ground. 20 Page 1 of 32 http://mc.manuscriptcentral.com/ppp Permafrost and Periglacial Processes 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 For Peer Review 22 1. Introduction 23 Environmental processes in mid-latitude high mountains are subject to post-Little Ice Age (LIA) climatic 24 evolution, which can be summarised as cold geomorphological processes that lose intensity and rise in 25 altitude.1 This fact has conditioned the total deglaciation of many of these mountains, including those on the 26 Mediterranean ranges, as well as a dramatic reduction in enclaves that are still glaciated.2 This is the case of 27 two of the three Iberian mountain ranges that hosted glaciers during the LIA, namely the Picos de Europa 28 (Cantabrian Mountains) and Sierra Nevada (Betic Range). Regarding the Picos de Europa, there is 29 geomorphological evidence and occasional written witness accounts of the existence of glaciers at the end of 30 the 19th century.3,4,5 With regards to the Sierra Nevada there are, from the 17th century on, numerous 31 historical documents, travellers’ accounts, old photographs and geomorphological sketches6,7 that also testify 32 to the existence of glaciers, together with clear sedimentological evidence8,9,10. Both historical and natural 33 records allowed us to infer the maximum expansion of these glaciers during the LIA and their subsequent 34 progressive disappearance7,8. 35 36 The climatic cooling that took place in the Iberian Peninsula during the LIA lasted from 1300 to 1850 CE, 37 with various blasts of cold and humidity that in the case of the Sierra Nevada involved the formation of small 38 glaciers at the foot of the highest peaks of the Iberian Peninsula, as well as a decrease in the altitude of the 39 periglacial belt.1 The glacier at the foot of the Mulhacén peak was formed around 1440 and lasted until 1710 40 CE,8 while the glacier that developed in the northern Veleta cirque gradually lost thickness and extent from 41 the early 19th century on, until it completely disappeared in the mid-20th century.7 The increase in 42 temperature recorded since the last cold phases of the LIA and up to the present day has been quantified in the 43 Sierra Nevada at 0.93 ºC,8 a very similar value to the one recorded at other Iberian ranges like the 44 Pyrenees.5,11 45 46 This temperature increase since the end of the LIA is much more pronounced in the mountain areas than in 47 the lowlands,12 which has led to changes in the intensity and spatial distribution of cold geomorphological 48 processes.13 It has also resulted in an intensification of the paraglacial response,14 an accelerated degradation 49 of alpine permafrost,15 and alterations in biogeographic dynamics in European high mountain environments, Page 2 of 32 http://mc.manuscriptcentral.com/ppp Permafrost and Periglacial Processes 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 For Peer Review 50 with a geographic redistribution of some plant species that tend to move up to higher altitudes.16 In the case of 51 the Sierra Nevada, due to its latitudinal position and geographical characteristics, changes resulting from the 52 end of the LIA still have a significant impact on ecosystem dynamics typical of high semi-arid Mediterranean 53 mountains. This is particularly relevant at summit level where periglacial processes are the main driver of 54 environmental dynamics.17,18 From this perspective, since the early 2000s we have been monitoring different 55 landforms of the Sierra Nevada's current periglacial belt that are located in cirque floors, headwaters of 56 valleys and summit plateaus. The main objective has been to relate the current activity of monitored 57 landforms with the thermal regime of the ground and of the air, as well as to evaluate their implications on the 58 geomorphological evolution of the Sierra Nevada’s high mountain landscape. In this article we summarise the 59 results on the thermal evolution over a fifteen-year period in southern Europe’s highest massif in order to give 60 answer to the following questions: 61 - What is the spatial distribution of permafrost and of seasonally frozen ground in the massif? 62 - What are the factors controlling the existence of permafrost and the thermal regime of seasonal frozen 63 ground in the Sierra Nevada? 64 - What are the implications of soil thermal regime on the present-day geomorphological processes 65 prevailing today in the massif? 66 67 2. Study area 68 The study area is located at the westernmost fringe of the Sierra Nevada National Park (37º 03'N / 3º 22'W), a 69 massif that encompasses a wide range of ecosystems characteristic of Mediterranean high mountains. It is 70 situated in the SE of the Iberian Peninsula and forms the highest mountain sector of the Iberian Peninsula 71 (Mulhacén, 3482 m, Veleta, 3398 m). 72 73 The climatic conditions that currently prevail in the Sierra Nevada are typical of semi-arid Mediterranean high 74 mountains. At 2500 m, the mean annual air temperature (MAAT) is 4.4 ºC and mean annual precipitation is 75 710 mm (1965-1992). At the summits (3300-3400 m) the MAAT is 0 ºC (2003-201323) and the snow and 76 frozen soil can persist, in an irregular manner that depends on the location, from early November to mid-June. 77 The warm season is very short and dry, with a mean monthly air temperature of 10-11 ºC in July and August Page 3 of 32 http://mc.manuscriptcentral.com/ppp Permafrost and Periglacial Processes 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 For Peer Review 78 at the summit level.24,25 These climatic conditions favour the existence of a periglacial belt from ca. 2650 m in 79 altitude, with very active periglacial processes above 2800-2900 m. Present-day processes and landforms 80 associated with current geomorphological dynamics depend on the combined behaviour of ice in the ground, 81 snow, wind and meltwater according to the altitude, orientation and the configuration of the relief. Plant cover 82 is scarce, scattered and of the cryoromediterranean xeric type, mainly consisting of grasses (Festuca clementei 83 and F. indigesta). Only some cirque floors and high valleys include a few wetlands (locally named 84 borreguiles) in poorly drained environments fed by snow-melt water.26 85 86 The current landscape, shaped in strata of Paleozoic micachists that were highly tectonised by the alpine 87 orogeny,19 stands out due to the fact that it contains the southernmost glacial and periglacial landforms in 88 Europe.20,21 Glacial activity reached the maximum development in the high areas of the valleys, in their 89 headwaters and slopes above 2500 m. Large cirques were carved by Quaternary glaciers, which deposited 90 sediments in the valley bottoms forming different moraine systems above 1900-2000 m. According to Be10 91 cosmogenic dates, sedimentary and erosive records show ages of glacial phases ranging from 135 ka to 300 92 years.22 This is indicative of the occurrence of glacial activity since phases prior to the Last Glaciation up 93 until the LIA, when the summits intensely affected by periglacial processes included small glaciers in 94 sheltered areas of the highest glacial cirques, in some of which remnants of ice still persist under a thick 95 debris cover.18 According to historical documents, the lower limit of the periglacial processes in the mid-19th 96 century was probably located at around 2435 m, ca. 200 m below the current one.7 97 98 The most significant landforms distributed across the high lands of the Sierra Nevada coincide with the 99 headwaters of the most important valleys (Lanjarón, Trevélez, Dílar, etc.) and the summit plateaus. 100 Quaternary glacial processes and postglacial periglacial activity have left behind a wide variety of landforms 101 typical of cold climates, such as moraines, over-deepened basins occupied by lakes and steep cirque walls and 102 ridges, talus slopes, rock glaciers, protalus lobes, solifluction landforms, etc. The summit plateaus, which 103 were former erosion surfaces, must have acted as cryoplanation terraces during glacial phases. These 104 environments include periglacial metric-size sorted circles, which tend to form block streams when the slope 105 increases (e.g. the summit plateaus of Machos and Mulhacén, 3300-3400 m).20 Page 4 of 32 http://mc.manuscriptcentral.com/ppp Permafrost and Periglacial Processes 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 For Peer Review 106 107 The study area encompasses abundant periglacial landforms in the western and highest sector of the massif, 108 whose activity is controlled by the local climatic regime and their microtopographic setting. We monitored 109 the soil thermal regime and landform dynamics in different enclaves of the massif (Figure 1): 110 111 Figure 1 112 113 - Veleta unit 114 The peak constituted a hörn during the Pleistocene including different glacial cirques at its base with ice 115 tongues radially spread towards the adjoining valleys. This unit includes several sites: 116 - Veleta peak (3398 m). This is the highest sector of the unit, dominated by bedrock and debris 117 cover resulting from frost weathering (Figure 2). 118 - Machos plateau (3297 m). Flat summit plateau located in the eastern fringe of the Veleta cirque. It 119 is strongly affected by recurring absences of snow in winter, and covered with thick layers of 120 debris that form periglacial sorted circles in the surface. 121 - Veleta cirque (3100-3150 m). It includes the basin of the Guarnón cirque, which is affected by 122 active paraglacial processes. During the LIA it included a small glacier, from which some relict ice 123 and permafrost still remain under debris cover.18,27,28 124 125 - Rio Seco cirque (3000-3050 m) and headwaters of San Juan valley (2800-2900 m) 126 Rio Seco is a wide south-facing glacial cirque, while the San Juan Valley is a narrow U-shaped glacial 127 valley facing north. The headwaters of both valleys were heavily glaciated during the Last Glaciation, and 128 wetlands formed during the Holocene including abundant solifluction features, generally next to long- 129 lying snow patches.29 130 131 Figure 2 132 133 3. Methods Page 5 of 32 http://mc.manuscriptcentral.com/ppp Permafrost and Periglacial Processes 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 For Peer Review 134 The central aim of this work is to provide a review and new data about present-day activity of periglacial 135 processes and their relationship with the ground thermal regime in different landforms across the Sierra 136 Nevada (Table 1). On this occasion we are updating the data and providing the most extensive and complete 137 review of the thermal regime of a southern massif in Europe, complementing previous works that always dealt 138 with partial topics.18,23,24,25,27,29,30,31,32,33,34,35 139 140 Table 1 141 142 3.1 Air and soil thermal regime 143 The first dataloggers used in this research were of the TinyTalk-II type (accuracy of ± 0.5 °C), which were 144 replaced in 2006 by Universal Temperature Loggers (UTL-1 and 2; accuracy of ± 0.1 °C) type and 145 complemented in recent years by Hobo U12 and Hobo Pendant devices (accuracy of ± 0.25 °C). In all cases, 146 they stored data continuously at 2-hour intervals from the end of August of one year to the end of August of 147 the following year, when the data was captured and the batteries replaced. A radiation shield was used for 148 logging air temperatures at a mast at the top of the Veleta peak (Figure 2), although no temperatures were 149 recorded from August 2001 to August 2003 at this site due to the failure of the datalogger. Monitoring of the 150 soil temperatures at different depths began at three enclaves in August 2001 and continued until August 2016. 151 The number of monitoring sites was increased, while sometimes the monitoring was discontinuous at other 152 sites (Figure 2). Remarkably, a 114.5 m deep borehole was drilled in the bedrock of the Veleta peak in August 153 2000 within the Permafrost and Climate Change in Europe (PACE) project, allowing to monitor bedrock 154 temperatures at the highest lands of the massif; however, temperature monitoring was limited to the 155 shallowest 60 m because of the presence of water in the deepest layers due to the break of the pipe23. We 156 present mean temperatures for each of the monitoring sites as well as the average number of days with freeze- 157 thaw (FT) cycles, which were calculated as those days recording temperatures both < −0.5 °C and > +0.5 158 °C.36 159 160 3.2 Control of landform dynamics Page 6 of 32 http://mc.manuscriptcentral.com/ppp Permafrost and Periglacial Processes 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 For Peer Review 161 Ground temperature control was carried out in parallel with the monitoring of landforms and their relationship 162 to local morpho-topographic and topoclimatic conditions. In the Veleta geomorphological unit, the rock 163 glacier located in the Veleta cirque was monitored by tracking and controlling fixed monitors installed on its 164 surface, which also allowed us to analyse the volumetric changes taking place here. The values were obtained 165 based on different geomatics techniques, including classic total station topography, Global Navigation 166 Satellite System and photogrammetry and Terrestrial Laser Scanner, which have been described in detail in 167 Gómez-Ortiz et al.18. This was complemented with tracking of the summer snow cover in the Veleta cirque 168 obtained through geo-referenced oblique and vertical digital photographs taken from fixed points.35 The 169 monitoring of the displacement rates of solifluction lobes in Rio Seco and San Juan valleys was carried out 170 following the procedures described in Oliva37 and Oliva et al.29,33,38 171 172 4. Results and interpretation 173 The evolution of air and soil temperature in different landforms during the observation period enables us to 174 contextualise the thermal regime and geomorphic processes inferred at the various control points (Figure 1, 175 Table 2). 176 177 Table 2 178 179 4.1 Air temperatures 180 The MAAT at the Veleta peak between 2003 and 2016 was 0.5 ºC, with marked variability showing negative 181 temperatures in 2008-2009 (-1.7 ºC) and positive values in 2011-2012 and 2015-2016 (1.1 ºC) and in 2013- 182 2014 (1.5 °C; Figure 3a, Table 2). Temperatures < -25 ºC and > +15 ºC were detected during the coldest and 183 warmest days. On average, temperature was always negative in 29% of the days, alternately positive and 184 negative in the 32% of the days and always positive in the 39% of the days.23 These persistently positive 185 mean monthly temperatures at 3400 m over 5 months (generally from May to October) explain why cold- 186 climate geomorphological processes are restricted to the highest altitudes of the massif, particularly inside the 187 northern glacial cirques. 188 Page 7 of 32 http://mc.manuscriptcentral.com/ppp Permafrost and Periglacial Processes 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 For Peer Review 189 Figure 3 190 191 4.2 Ground thermal regime 192 4.2.1 Bedrock of the Veleta peak 193 Temperature monitoring throughout the deep borehole allows us to characterise the thermal evolution in the 194 bedrock of the Sierra Nevada’s highest sectors, as well as to frame the thermal regime of the ground with the 195 topography, the nature of the surface formation (substrate vs. sediment) and the morphogenic environment in 196 other monitoring sites of the massif. 197 198 Mean annual temperature in the borehole was always positive, with values ranging from 3.2 °C at 0.5 m to 2.4 199 °C at 20 m depth (Figure 3b). Soil temperature up to 1.2 m shows high inter-annual and intra-annual 200 variability, gradually decreasing in depth until mean annual values stabilise at approximately 2.5 °C from 4 m 201 onwards (Table 2). The bedrock temperatures several degrees above the freezing point demonstrate that there 202 are no widespread permafrost conditions at the high peaks of the Sierra Nevada. 203 204 The timing of the seasonally frozen layer depends on when snow stabilises on the ground, as well as when it 205 melts, although the exposure to strong winds means that the area can be snow-free even during the winter. In 206 general, frozen ground conditions extend from late October to June at depths of 0.6 to 2 m, with mean ground 207 temperature during this period of -3.3 °C and -1.4 °C, respectively. In addition, between 1 and 4 freeze-thaw 208 cycles were recorded in early fall and late spring at depths until 1.2 m23, despite the fact that air temperatures 209 measured up to 36.5 and 30 cycles during the freezing and thawing seasons, respectively. Inter-annual and 210 intra-annual ground temperatures remained stable below 20 m until 2009, when a temperature increase of 0.2 211 ºC was detected at 60 m depth, which was associated with a lowering air temperature trend in the last 212 decade.23 213 214 4.2.2 Sorted circles in the Machos summit plateau 215 Altitude and morpho-topographic position determine the ground thermal regime in this environment that 216 forms a plateau (5.5 Ha) located at the summit line between Veleta peak and the Machos plateau, and includes Page 8 of 32 http://mc.manuscriptcentral.com/ppp Permafrost and Periglacial Processes 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 For Peer Review 217 an extensive field of patterned grounds (1.2 Ha), namely sorted circles and sorted stripes31. They are probably 218 currently inactive as suggested by the presence of an abundant lichen cover. No evidence has been found that 219 this plateau was glaciated in the past, when glaciers developed in the surrounding cirques and valley 220 floors.28,39 The high incoming solar radiation due to a lack of topographical obstacles, as well as the unstable 221 snow cover caused by the N and NW winds, determine a strong daily temperature amplitude range that is not 222 reflected in the average values (Table 2) between the surface level (5 cm) – with extreme temperatures 223 between +40 and -20 ºC – and the deeper layers (50 cm), with extreme values between +13 and -7 ºC. 224 225 The poor protection provided by the snow during the cold season causes the ground to freeze for prolonged 226 periods (ca. 6-7 months) and to depths > 50 cm (Figure 3c), with brief or inexistent isothermal periods 227 characteristic of enclaves with long-lasting snow cover.39 The thermal contrast between the monitored levels 228 is also reflected in the value of the daily temperature amplitudes (8º C at the surface, 0.4º C at depth) and in 229 the mean number of the freeze-thaw cycles (66 at the surface, 6 at depth). The short supply of snow-melt 230 water in this semi-arid environment also explains that these periglacial features are no longer active, being 231 inheritance from other periods when periglacial dynamics were more intense. 232 233 4.2.3 Rock glacier of the Veleta cirque 234 The rock glacier that exists inside the Veleta cirque sits on a frozen body that constitutes the remnants of a 235 glacier located at the head of the Guarnón valley during the LIA. Its formation is the result from postglacial 236 geomorphological processes affecting the area during the post-LIA glacier decay.18 237 238 The overlying debris cover is affected by alternating freezing-thawing periods throughout the year (Figure 239 3d). The five loggers installed at different depths in the active layer of the rock glacier up to 1.5 m show high 240 temperature variability strongly influenced by the presence of snow during the warm season. The mean 241 annual temperature and the extreme values at each level show a decrease in temperature, with values of -1 ºC 242 at 1.5 m depth, where the maximum temperature of the record was 0.2 ºC (Table 2). This suggests that below 243 this depth the ground is permanently frozen with temperatures ≤ 0º C, demonstrating the existence of frozen 244 masses at deeper levels (relict glacial ice and permafrost). In addition, the rock glacier is mostly composed of Page 9 of 32 http://mc.manuscriptcentral.com/ppp Permafrost and Periglacial Processes 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 For Peer Review 245 large boulders (up to 2-3 m wide), which favours that colder and denser air flows out from the rock glacier 246 front during the summer months. This leads to cooler temperatures at the rock glacier terminus as well as 247 along the edges of the landform, thus contributing to the preservation of the frozen body. 40 248 249 Figure 4 250 251 Ground temperature shows a high seasonal and annual variability highly controlled by the presence of snow 252 in the cirque floor (Table 2). In late August there are years when the Veleta cirque is snow free, and others in 253 which virtually the entire cirque floor is covered in snow (Table 3). Both situations have different 254 repercussions on the ground thermal regime, as well as on the geomorphological response of the rock glacier. 255 Table 3 shows the mean surface displacement (subsidence and advance) of the fixed baseline controls 256 installed in the surface of the rock glacier. The magnitude and direction of the advance of this periglacial 257 feature is reflected in Figure 4a. No displacement data are available from the 2009-2010, 2010-2011 and 258 2012-2013 periods because the surface of the rock glacier remained covered by more than 2 m of snow, 259 making data collection impossible (Figure 5). 260 261 Figure 5 262 263 By analysing different transversal transects at various levels of the rock glacier by means of photogrammetry 264 and a terrestrial laser scanner,41 we estimated average sinking values of 3.97 m and an average advance of 265 1.25 m, which hardly changed the morphometry of the 2001 front (Figure 4b). Assuming that the underlying 266 frozen body consist of continuous layers and homogeneous thicknesses arranged between the detrital slope 267 attached to the Veleta rock wall and the internal ridge of the moraine, the subsidence data obtained from the 268 surface layer of the rock glacier (area of 3815 m2) suggests that the volume loss of the underlying frozen 269 masses amounts to 15137.4 m3 during the study period. 270 271 Table 3 272 Page 10 of 32 http://mc.manuscriptcentral.com/ppp Permafrost and Periglacial Processes 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 For Peer Review 273 4.2.4 Solifluction landforms in the Rio Seco cirque and San Juan valleys 274 The headwaters of the Sierra Nevada’s high valleys show no permanently negative ground temperatures 275 during the year, which indicates the absence of permafrost (Figure 6). Two vegetated solifluction lobes in the 276 Rio Seco cirque and in the San Juan valley showed average temperature values ranging from 3.6-3.9°C and 277 3.0-3.9°C, respectively, throughout the first metre below the surface and with low variability deeper in the 278 ground (Table 2). 279 280 Figure 6 281 282 The date of the first snow fall impacts the depth of seasonal frost, though the stabilisation and thickness of the 283 snow cover on the ground is highly variable from year to year. Snowy years lead to nearly isothermal regime 284 of the ground and thinner frost penetration, such as in 2008-2009 and 2010-2011 (Figure 6), with a thickness 285 of the frozen layer ranging between a few cm and 20 cm; by contrast, it can reach up to 1 m in San Juan and 286 70 cm in Rio Seco in the years with least snowfall, like 2006-2007 and 2007-2008 (Figure 6). The persistence 287 and thickness of the snow also determines the intensity of the frost; in San Juan and Rio Seco lobes, the 288 absolute minimum temperatures at 2 cm below the surface were -10.8 and -8.5 ºC, respectively. In turn, it also 289 determines the frequency of daily oscillations around 0° C, which are limited to a small number of days and to 290 the shallowest sensors (up to 20 cm). In general, the ground remains frozen between November and May- 291 June,34 with significant variations depending on the prevailing climatic conditions, and with a deeper frozen 292 layer in the northern San Juan valley than in the southern Rio Seco cirque. 293 294 In addition to the temperature monitoring, the displacement of solifluction landforms was also measured. In 295 the case of the Rio Seco lobe, no displacement was detected between 2005 and 2011, while in the San Juan 296 lobe the stakes reported very limited movement between 0.4 and 0.8 cm yr–1.29 The northern exposure of San 297 Juan valley facilitates greater persistence of long-lasting snow patches, thus favouring surface saturation and 298 solifluction processes, as suggested by the average values obtained in the San Juan lobes with higher rates 299 (0.3 to 0.9 cm yr–1) than those of Rio Seco (0.2 to 0.5 cm yr–1). In all cases, these movements show annual Page 11 of 32 http://mc.manuscriptcentral.com/ppp Permafrost and Periglacial Processes 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 For Peer Review 300 rates below 1 cm yr–1, being higher in years with more snow. This confirms the key role that snow-melt plays 301 in the activity of solifluction processes in this semi-arid environment.33,38 302 303 5. Discussion 304 The series of air and soil temperature data examined in this research are the longest in a southern European 305 high massif, and they show an absence of widespread permafrost conditions in the massif, with mean annual 306 bedrock temperatures at summit level (3300-3400 m) of 2.5 ºC, where the MAAT is 0.5 ºC. As in other 307 Iberian mountains like the central sector of the Cantabrian Mountains in Picos de Europa, the occurrence of 308 permafrost is strongly conditioned by the past geomorphological processes, namely the existence of glaciers 309 during the LIA.42,43 This is also the case in several massifs in the Central Pyrenees.14,44,45,46,47,48 310 311 5.1 Permafrost conditions in the Sierra Nevada since the Last Glaciation 312 During the coldest phases of the Last Glaciation, glaciers in the Sierra Nevada extended throughout the 313 headwaters of the valleys from the high cirques of both slopes, descending in the form of alpine tongues of up 314 to 8-9 km in length. Glaciers reached altitudes slightly lower than 2000 m on the northern slope of the Sierra 315 Nevada and around 2500 m on the southern side.28,39,49 As suggested by mountain glacier models based on 316 geomorphological evidence, during that phase summit plateaus must have remained mostly ice-free due to the 317 redistribution of snow by the wind, with an ELA located at 2525 m on the northern slope and 2650 m on the 318 southern slope. This means that temperatures at the peaks were approximately -4 to -6 ºC, which suggests the 319 existence of permafrost conditions.21 In some of these sectors, as in the case of the Machos plateau, currently 320 inactive metric-size sorted circles developed. Temperature loggers up to 50 cm deep in these landforms 321 reported average temperatures ranging from 1.7 to 2.0 ºC, which are very far from permafrost conditions. 322 Their similarity to currently active stone circles in other periglacial environments demonstrates that they 323 require a regime of permanently frozen ground with average values close to -4 to -6 ºC and very active 324 cryogenic processes.50,51 They are thus inherited features, as suggested by the presence of lichens and cryo- 325 xerophyte herbaceous vegetation in the surface. During the maximum ice extent of the Last Glaciation in the 326 Sierra Nevada, there were also hillsides up to 2500 m high that were not glaciated, so they must have had a Page 12 of 32 http://mc.manuscriptcentral.com/ppp Permafrost and Periglacial Processes 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 For Peer Review 327 soil thermal regime of permafrost, as suggested by the existence of rock glaciers outside the glaciated 328 environment.21 329 330 The increase in temperature recorded during the deglaciation begun in the Sierra Nevada around 19-20 331 ka28,39,52 – synchronously with the overall Last Glacial Maximum –53 favoured glacier retreat, as well as the 332 progressive shift of permafrost and periglacial processes at higher altitudes. From the onset of the deglaciation 333 until the beginning of the Holocene, there is evidence of existing different generations of rock glaciers, some 334 formed during the Oldest Dryas (17.5-14.7 ka; e.g. Mulhacén valley) and most of them developed during the 335 Younger Dryas (12.9-11.7 ka; e.g. Lanjarón, Rio Seco and Dílar valleys).49,52 As occurred during the post- 336 LIA phase in the rock glacier that exists in the Veleta cirque,18 the formation of permafrost-related features – 337 including rock glaciers and protalus lobes – must have been conditioned by highly active paraglacial 338 processes, with very unstable rock walls that produced large quantities of sediment, which must have trapped 339 ice that no longer featured glacial dynamics.14 This process has also been detected in other environments of 340 the Iberian mountains, like the Central54,55 and Eastern Pyrenees.56,57 Therefore, this probably means that these 341 were glacier-derived rock glaciers,58 suggesting that the elevation boundary for permafrost during the Late 342 Glacial must have been located at ca. 2800-3000 m in the high sections of recently deglaciated cirques. 343 344 Although some of these landforms remained active in the Sierra Nevada well into the Early Holocene and 345 stabilised at ca. 7-8 ka,52 the rise in temperature experienced during the Holocene prevented the occurrence of 346 permafrost conditions in most of the massif. During the Mid-Late Holocene the higher temperatures were 347 accompanied by increased aridity at the highest lands as suggested by lake records, which would imply less 348 snow cover in these areas.59 Current bedrock temperatures at the summits are several degrees above the 349 freezing point, as detected in the deep borehole of the Veleta peak where temperatures of 2.5 ºC in depth 350 show evidence of the absence of permafrost conditions.23 Considering these values, as well as the Holocene 351 climatic variability in the Northern Hemisphere, which has oscillated approximately 2 ºC during the current 352 interglacial,60 widespread permafrost conditions during the Holocene are not to be expected in the high lands 353 of the Sierra Nevada, despite the existence of cold phases in which small glaciers developed at the foot of the Page 13 of 32 http://mc.manuscriptcentral.com/ppp Permafrost and Periglacial Processes 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 For Peer Review 354 highest peaks, like during the Neoglacial period (2.8-2.7 ka cal BP), the Dark Ages (1.4-1.2 ka cal BP) or the 355 LIA (1300-1850 CE).1,8 356 357 During the LIA, the colder climatic conditions that prevailed in the Iberian Peninsula favoured the expansion 358 of glaciers in the Cantabrian Mountains, the Pyrenees and the northernmost cirques of the Sierra Nevada, 359 especially during the most humid phases, as well as the intensification of periglacial processes at lower 360 altitudes than the current ones.13 Current average temperatures were quantified at around 1 °C higher than in 361 1850 and 2 °C higher than during the Maunder Minimum (1645-1715).1 Considering that the MAAT at the 362 Veleta peak is 0.5 ºC at present (Table 2), MAATs during the LIA at elevations of 3300-3400 m must have 363 been ca. -2 °C during the coldest phases. However, the high thermal conductivity of the dark michaschist 364 substrate and the intensity and persistence of the sunshine during the warm season, as well as the current 365 ground values of 2.5 ºC, suggest that the LIA probably did not favour the expansion of permafrost in summit 366 surfaces. 367 368 5.2 Frozen ground and current geomorphic processes 369 The monitoring of the ground thermal regime and of the morphodynamics in the summits of the Sierra 370 Nevada since the beginning of 2000 confirms the major role of periglacial processes driven by seasonal frost 371 in the evolution of the landscape in this high Mediterranean mountain located in the far south of the European 372 continent. Temperature monitoring over a fifteen-year period in different topographical and geomorphological 373 settings allowed inferring the spatial distribution of permanently and seasonally frozen soil in the massif, as 374 well as determining the main factors controlling the ground thermal regime at the highest lands. 375 376 Currently, permafrost environments are sporadic, with geomorphological processes in the massif driven by 377 the presence of seasonal frost starting from altitudes of 2500-2600 m. The variability of snow cover in the 378 Sierra Nevada is the determining factor that explains the variations in ground temperatures (Figure 3 and 6). 379 Years of heavy snow fall with long-lying snow cover favour lower soil temperatures, although these are less 380 extreme and undergo smaller intra-annual oscillations; convers12ely, years with less snow fall give rise to 381 longer seasons of thawed soil, with greater temperature amplitude and higher average temperatures. This Page 14 of 32 http://mc.manuscriptcentral.com/ppp Permafrost and Periglacial Processes 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 For Peer Review 382 ground thermal regime highly dependent on the calendar of the first snow fall, as well as on the persistence 383 and thickness of the snow cover, has been observed in other mid-latitude mountain environments from 384 Iberia61,62 and other geographical locations across the world.63 In the case of the summits of the Sierra 385 Nevada, the shorter or longer duration of the snow not only impacts the ground thermal regime but also has 386 major geomorphological, hydrological and edaphic implications on landscape dynamics; it also conditions the 387 length of the vegetation growing cycle, which is very short, particularly at the summits.26 388 389 The data from the loggers placed at altitudes of 2800-3000 m in San Juan and Rio Seco valleys show that the 390 mean annual temperature of the soil is approximately 3-4 ºC, with a thawed season that lasts half the year and 391 which does not favour active solifluction, with displacements under 1 cm yr–1.10 Therefore, the existence of 392 permafrost conditions can be ruled out in most of the massif, as is the case of most mountains in the 393 Mediterranean alpine fringe outside the Alps.64 In fact, it was only at the Veleta cirque, in the sector where a 394 small glacier existed during the LIA, that permanently frozen ground conditions were detected. The increase 395 in temperature of ca. 1 °C that was observed since the second half of the 19th century caused its gradual 396 decline and disappearance from the middle of the 20th century, being subsequently replaced by paraglacial 397 dynamics. A 2-m thick debris cover detached from the Veleta rock wall and covered the stagnant glacier ice, 398 which favoured its overlying debris cover to freeze due to its contact with the frozen mass. This facilitated the 399 slow displacement of the surface blocks, the deformation of the frozen mass and the formation of an incipient 400 rock glacier.6,18 In the nearby Mulhacén cirque, where a small glacier disappeared around 1710 towards the 401 end of the Maunder Minimum,8 the paraglacial processes associated with the deglaciation of the enclave 402 fostered the development of a protalus lobe at the foot of the steep northern face of the Mulhacén peak.14 403 404 In fact, the temperature data recorded at the rock glacier of the Veleta cirque indicates the existence of mean 405 temperatures of -1.0 ºC at 1.5 m depth and lower values below that level, as revealed by the fact that the 406 underlying sediments always remained frozen as they were in contact with the top of relict glacial ice. 407 Therefore, the uppermost layer that freezes and thaws every year constitutes the active layer, with a highly 408 variable thickness during the study period dependent on the snow cover existing in the surface (Figure 3d). 409 However, dynamic control of this landform between 2002 and 2016 showed a continuous subsidence or Page 15 of 32 http://mc.manuscriptcentral.com/ppp Permafrost and Periglacial Processes 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 For Peer Review 410 collapse movement that is associated with a loss in the volume of its frozen basal mass, quantified as 15,137.4 411 m3 (Table 3). This pattern is also confirmed by geophysical measurements taken in 2009 which, when 412 compared to 1999 measurements, indicated that the frozen layer thinned and fragmented.6 In turn, the 413 occurrence of multiple collapses and subsidence in the surface of the rock glacier also corroborates the 414 degradation of frozen conditions under the surface. This same process was also observed in the detrital slopes 415 near the Mulhacen cirque’s protalus lobe, which are possibly also related to the degradation of the permafrost 416 conditions that prevail there (Oliva, unpublished data). 417 418 The degradation of relict ice and permafrost has been also detected in other Iberian high mountain 419 environments glaciated during the LIA, such as in the Pyrenees and the Cantabrian Mountains.13, 14 Similarly, 420 evidence of degradation of perennial ice deep in the ground has been also reported in several karstic 421 environments across the Mediterranean region: recent studies have reported a shrinkage of the ice volume 422 stored in ice caves as well as a decrease in extent of permanently frozen ground existing in these sporadic 423 permafrost environments in the Cantabrian Mountains,65 Pyrenees,66 Italy,67 Croatia68 or Greece,69 among 424 others. 425 426 In conclusion, the data recorded from 2001 to 2016 in different periglacial features across the high lands of 427 the Sierra Nevada shows evidence that seasonally frozen ground is the key driver of the present-day 428 geomorphological processes, since permafrost conditions are very sporadic and only connected to the 429 geomorphological setting inherited from the LIA, with a gradual loss in volume and subsequent debris cover 430 partly made up of sediment from ancient glaciers. The imbalance between current climatic conditions and the 431 thermal regime of these disconnected and isolated masses of permafrost and relict ice promotes their 432 accelerated degradation. Based on international reports that assume an increase in temperature and a decrease 433 in precipitation in the Mediterranean basin in the near future,70 these southernmost patches of permafrost in 434 the European continent will tend to disappear in the forthcoming decades. 435 436 6. Conclusions Page 16 of 32 http://mc.manuscriptcentral.com/ppp Permafrost and Periglacial Processes 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 For Peer Review 437 Periglacial dynamics prevailing nowadays in the semi-arid Mediterranean high mountains of the Sierra 438 Nevada are subject to current climatic conditions and reinforced by the bareness of the ground, since the 439 sparse cryo-xerophytic vegetation that covers them is unable to counteract the mechanical action of cryogenic 440 processes. These environmental conditions impose the response of ecosystems and landscape dynamics, 441 favouring widespread geomorphic processes in summit areas. 442 443 Periglacial processes are reworking the landscape shaped by Quaternary glaciers, and are currently the key 444 driver of environmental processes prevailing above 2500 m in the Sierra Nevada. Its effectiveness lies in the 445 seasonal action of the ice on the ground, generally reaching depths between 0.5 and 2 m; however, these 446 values are highly influenced by local climatic and morpho-topographic characteristics, especially the high 447 variability of the calendar, duration and thickness of the snow cover. Temperature monitoring carried out 448 from 2001 to 2016 showed that the highest peaks, located at 3300-3400 m, have a MAAT of 0.5 ºC, with 449 subsurface temperatures of approximately 2.5 ºC. Above 2800 m, soil temperatures are approximately 3-4 °C, 450 with values around 2 °C at the summit plateaus at 3300-3400 m. This demonstrates the absence of widespread 451 permafrost in the massif, which was only detected in enclaves that were glaciated during the LIA, as in the 452 case of the Veleta cirque. 453 454 Paraglacial processes associated with glacier retreat since the second half of the 19th century led to the burial 455 of stagnant glacier ice by debris, which favoured the formation of some patches of permafrost in these 456 environments. The monitoring of temperatures and surface dynamics showed that these remnants of relict 457 glacier ice and permafrost from the LIA covered by layers of debris are undergoing a process of degradation. 458 These enclaves, unusual in the massif of the Sierra Nevada and scarce in other Mediterranean mountains, 459 make it essential to continue monitoring over the next few years due to their importance as environmental 460 geoindicators of climate change in the south of the Iberian Peninsula. At the same time, within the protected 461 areas of the Sierra Nevada National Park, it is important to designate these rapidly changing environments as 462 areas of geomorphological interest due to its unique scientific and heritage value and significance in the 463 recent geological history of these mountains, so as to ensure its necessary preservation and proper 464 management. Page 17 of 32 http://mc.manuscriptcentral.com/ppp Permafrost and Periglacial Processes 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 For Peer Review 465 466 Acknowledgements 467 Marc Oliva is supported by the Ramón y Cajal Program (RYC-2015-17597) and the Research Group 468 ANTALP (Antarctic, Arctic, Alpine Environments; 2017-SGR-1102) funded by the Government of Catalonia 469 through the AGAUR agency. The work complements the research topics examined in the CGL2015-65813-R 470 and CTM2017-87976-P projects of the Ministry of Economy and Competitiveness, Spain. We are grateful to 471 field support offered by the National Park of Sierra Nevada. 472 473 References 474 1 Oliva M, Ruiz-Fernández J, Barriendos M, Benito G, Cuadrat, JM, García-Ruiz JM, Giralt S, Gómez- 475 Ortiz A, Hernández A, López-Costas O, López-Moreno JI, López-Sáez JA, Martínez-Cortizas A, Moreno 476 A, Prohom M, Saz MA, Serrano E, Tejedor E, Trigo R, Valero-Garcés B, Vicente-Serrano S. The Little 477 Ice Age in Iberian mountains. Earth-Sci Rev. 2018;177:175-208. 478 2 Hughes PD. Little Ice Age glaciers and climate in the Mediterranean mountains: a new analysis. Cuadern 479 Investig. 2018;44(1):15-45. 480 3 González-Trueba JJ. La Pequeña Edad del Hielo en los Picos de Europa (Cordillera Cantábrica, NO de 481 España). Análisis morfológico y reconstrucción del avance glaciar histórico. 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Salvador-Franch F, Salvà-Catarineu M, Oliva M, Gómez-Ortiz A. Régimen térmico del suelo y dinámica 547 periglaciar en la planicie somital del Collado de los Machos (Sierra Nevada). In: González-Díez A, ed. 548 Avances de la Geomorfología en España 2010-2012. Santander, Spain: Ediciones Universidad de 549 Cantabria; 2012:637-640. 550 26. Molero-Mesa J, Pérez-Raya F, Valle-Tendero F, eds. Vegetación. Vegetación climácica. In: Parque 551 Natural de Sierra Nevada. Paisaje, fauna, flora e itinerarios. Madrid, Spain: Rueda; 1992:107-130. 552 27. Gómez-Ortiz A, Palacios D, Ramos M, Tanarro LM, Schulte, Salvador-Franch F. Location of permafrost 553 in marginal regions: Corral del Veleta, Sierra Nevada, Spain. Permafrost Periglac. 2001;12:93-110. 554 28. Gómez-Ortiz A, Palacios D, Oliva M, Salvador-Franch F, Salvà-Catarineu M. The deglaciation of Sierra 555 Nevada (Spain): synthesis of current knowledge and new contributions. Cuadern Investig. 556 2015;41(2):409-426. 557 29. 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Page 20 of 32 http://mc.manuscriptcentral.com/ppp Permafrost and Periglacial Processes 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 For Peer Review 588 40. Colucci RR, Forte E, Ž ebre M, Maset E, Zanettini C, Guglielmin, M. Is that a relict rock glacier? 589 Geomorphology. 2019;330:177-189. 590 41. Sanjosé JJ, Gómez-Ortiz A, Sánchez-Fernández M, Salvador-Franch F, Salvà-Catarineu M, Atkinson A. 591 Técnicas geomáticas aplicadas al glaciar rocoso del Corral del Veleta, durante el periodo 2001-2016. In: 592 Ruiz-Fernández J, García-Hernández C, Oliva M, Rodríguez-Pérez C, Gallinar D, eds. Ambientes 593 periglaciares: avances en su estudio, valoración patrimonial y riesgos asociados. Oviedo, Spain: 594 Publicaciones de la Universidad de Oviedo; 2017:171-179. 595 42. Serrano E, González-Trueba JJ, Sanjosé JJ, Del Río LM. Ice patch origin, evolution and dynamics in a 596 temperate high mountain environment: the Jou Negro, Picos de Europa (NW Spain). Geogr Ann A. 597 2011;93A:57-70. 598 43. Ruiz-Fernández J, Oliva M, Hrbáček F, Vieira G, García-Hernández C, Gallinar D. Soil temperatures in 599 an Atlantic high mountain environment: The Forcadona buried ice patch (Picos de Europa, NW Spain). 600 Catena. 2017;149(2):637-647. 601 44. Serrano E, Agudo R, Delaloye R, González-Trueba JJ. 2001. Permafrost distribution in the Posets massif, 602 Central Pyrenees. Norsk Geol Tidsskr. 2001;55:245-252. 603 45. Serrano E, Sanjosé JJ, Agudo C. Rock glacier dynamics in a marginal periglacial high mountain 604 environment: flow, movement (1991–2000) and structure of the Argualas rock glacier. The Pyrenees. 605 Geomorphology. 2006;74:286-296. 606 46. Lugon R, Delaloyé R, Serrano E, Reynard E, Lambiel C, González Trueba JJ. Permafrost and Little Ice 607 Age relationships, Posets massif, Central Pyrenees, Spain. Permafrost Periglac. 2004;15:207-220. 608 47. González-García M. La Alta montaña periglaciar en el Pirineo Central español. Procesos, formas y 609 condiciones ambientales (Ph.D. thesis). Málaga, Spain: University of Málaga; 2014. 610 48. González-García M, Serrano E, Sanjosé, J.J., González-Trueba JJ. Surface Dynamic of a Protalus Lobe in 611 the Temperate High Mountain, Western Maladeta, Pyrenees. Catena. 2016;149(3):689-700. 612 49. Gómez-Ortiz A, Palacios D, Palade B, Vázquez-Selem L, Salvador-Franch F, Tanarro LM, Oliva M. La 613 evolución glaciar de Sierra Nevada y la formación de glaciares rocosos. B Asoc Geogr Esp. 2013;61:139- 614 162. 615 50. Washburn AL. Geocryology. A Survey of Periglacial Processes and Environments. London, UK: Edward 616 Arnold; 1979. 617 51. French HM. The periglacial environment. Third ed. New York, USA: Wiley; 2007. 618 52 Palacios D, Gómez-Ortiz A, Andrés N, Salvador-Franch F, Oliva M. Timing and new geomorphologic 619 evidence of the Last Deglaciation stages in Sierra Nevada (southern Spain). Quaternary Sci Rev. 620 2016;150:110-129. 621 53. Clark PU, Dyke AS, Shakun JD, Carlson AE, Clark J, Wohlfarth B, Mitrovica JX, Hostetler SW, McCabe 622 AM. The last glacial maximum. Science. 2009;325:710-714. 623 54. Palacios D, Gómez-Ortiz A, Andrés N, Vázquez-Selem L, Salvador-Franch F, Oliva M. Maximum extent 624 of Late Pleistocene glaciers and Last Deglaciation of La Cerdanya mountains, Southeastern Pyrenees. 625 Geomorphology. 2015;231:116-129. 626 55. Palacios D, Andrés N, García-Ruiz JM, Schimmelpfennig I, Campos N, Leanni L, ASTER Team. 627 Deglaciation in the central Pyrenees during the Pleistocene-Holocene transition: timing and 628 geomorphological significance. Quaternary Sci Rev. 2017;150:110-129. Page 21 of 32 http://mc.manuscriptcentral.com/ppp Permafrost and Periglacial Processes 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 For Peer Review 629 56. Palacios D, Andrés N, López-Moreno JI, García-Ruiz JM. Late Pleistocene deglaciation in the upper 630 Gállego Valley, Central Pyrenees. Quaternary Res. 2015;83:397-414. 631 57. Andrés N, Gómez-Ortiz A, Fernández-Fernández JM, Tanarro LM, Salvador-Franch F, Oliva M, Palacios 632 D. Timing of deglaciation and rock glacier origin in the southeastern Pyrenees: a review and new data. 633 Boreas. 2018;47(4):1050-1071.. 634 58. Whalley B, Martin HE. Rock glaciers in Trollaskagi, their origin and climatic significance. Münchener 635 Geogr Abh. 1994;12:289-308. 636 59. Oliva M, Gómez-Ortiz A, Schulte L. Tendencia a la aridez en Sierra Nevada desde el Holoceno Medio 637 inferida a partir de sedimentos lacustres. B Asoc Geogr Esp. 2010;52:27-42,349-351. 638 60. Mayewski PA, Rohling EE, Stager C, Karlén W, Maasch KA, Meeker LD, Meyerson EA, Gasse F, Van 639 Kreveld S, Holmgren K, Leethrop J, Rosqvist G, Rack F, Staubwasser M, Schneider RR, Steig EJ. 640 Holocene climate variability. Quaternary Res. 2004;62(3):243-255. 641 61. Palacios D, Andrés N. Morfodinámica supraforestal actual en la Sierra de Guadarrama y su relación con la 642 cubierta nival: el caso de Dos Hermanas-Peñalara. In: Peña Monné JL, Sánchez Fabre M, Lozano-Tena 643 MV, eds. Procesos y formas periglaciares en la montaña mediterránea. Teruel, Spain: Instituto de Estudios 644 Turolenses; 2000:235-264. 645 62. Palacios D, Andrés N, Luengo E. Distribution and effectiveness of nivation in Mediterranean mountains: 646 Peñalara (Spain). Geomorphology. 2003;54:157-178. 647 63. Zhang T. Influence of the seasonal snow cover on the ground thermal regime: An overview. Rev Geophys. 648 2005;43(4),RG4002. 649 64. Oliva M, Žebre M, Guglielmin M, Çiner A, Vieira G, Bodin X, Andrés N, Colucci RR, García-Hernández 650 C, Hughes P, Mora C, Nofre J, Palacios D, Pérez-Alberti A, Ribolini A, Ruiz-Fernández J, Sarıkaya MA, 651 Serrano E, Urdea P, Valcárcel M, Woodward J, Yıldırım C. Permafrost conditions in the Mediterranean 652 region since the Last Glaciation. Earth-Sci Rev. 2018;185:397-436. 653 65. Gómez-Lende M, Berenguer F, Serrano E. Morphology, ice types and thermal regime in a high mountain 654 ice cave, first studies applying terrestrial laser scanner in the Pena Castil ice cave (Picos de Europa, 655 Northern Spain). Geogr Fis Din Quat. 2014;37:141-150. 656 66. Serrano E, Gómez-Lende M, Belmonte A, Sancho C, Sánchez-Benítez J, Bartolomé M, Leunda M, 657 Moreno A, Hivert B. Ice caves in Spain. In: Perşoiu A, Lauritzen SE, eds. Ice Caves. Part II: Ice Caves of 658 the World, 2018:625-655. 659 67. Maggi V, Colucci RR, Scoto F, Giudice G, Randazzo L. Ice caves in Italy. In: Perşoiu A, Lauritzen SE, 660 eds. Ice Caves. Part II: Ice Caves of the World, 2018:399-423. 661 68. Buzjak N, Bočić N, Paar D, Bakšić D, Dubovečak V. Ice caves in Croatia. In: Perşoiu A, Lauritzen SE, 662 eds. Ice Caves. Part II: Ice Caves of the World, 2018 335-369. 663 69. Pennos C, Styllas M, Sotiriadis Y, Vaxevanopoulos M. Ice caves in Greece. In: Perşoiu A, Lauritzen SE, 664 eds. Ice Caves. Part II: Ice Caves of the World, 2018:385-397. 665 70. IPCC Climate Change. The Physical Science Basis. Contribution of Working Group I to the Fifth 666 Assessment Report of the Intergovernmental Panel on Climate Change. Cambridge, UK: Cambridge 667 University Press; 2013. 668 Page 22 of 32 http://mc.manuscriptcentral.com/ppp Permafrost and Periglacial Processes 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 For Peer Review 670 Table 1. Study sites, geomorphological settings and monitoring characteristics. 671 Study site Geomorphological setting Site altitude (m) Temperature monitoring Dynamic control of landforms Veleta peak (PV-air) Summit plateau 3398 Air temperatures - Veleta peak (PV) Summit plateau 3380 Control of bedrock temperatures with a chain of sensors inside the borehole at depths of 0.2, 0.5, 1, 2.5, 4, 7.5, 10, 12.5, 15, 20 and 60 m - Machos summit (CM) Summit plateau 3297 Control of soil temperatures with sensors placed in the ground at depths of 0.05, 0.2 and 0.5 m Geomorphic evidence Veleta cirque (CV) Glacial cirque, rock glacier 3107 Control of soil temperatures with a chain of sensors inside a shallow borehole at depths of 0.05, 0.2, 0.5, 1 and 1.5 m Different geomatics techniques18 Rio Seco (RS) Glacial cirque, solifluction lobe 3005 Control of soil temperatures with sensors placed in the ground at depths of 0.02, 0.1, 0.2, 0.5 and 1 m Stake measurements 29, 33 San Juan (SJ) Glacial valley, solifluction lobe 2817 Control of soil temperatures with sensors placed in the ground at depths of 0.02, 0.1, 0.2, 0.5 and 1 m Stake measurements 29, 33 672 673 Page 23 of 32 http://mc.manuscriptcentral.com/ppp Permafrost and Periglacial Processes 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 For Peer Review 675 Table 2. Mean annual temperature values at the different monitoring sites and depths, together with 676 the annual mean of FT cycles. 677 Depth Years (m) 01-02 02-03 03-04 04-05 05-06 06-07 07-08 08-09 09-10 10-11 11-12 12-13 13-14 14-15 15-16 Mean FT PV-air air -- -- 0.8* 0.8 0.4* 0.0 0.5* -1.7 0.5 0.6 1.1 0.0 1.5 0.8 1.1 0.5 108.0 PV 0.2 -- 2.9 2.8 3.8 2.8 2.2 2.6 2.8 2.1 2.4 4.2 2.6 1.7 3.3 2.8* 2.8 5.5 0.5 -- 3.3 3.2 4.3 3.2* 2.7 2.9 3.2 2.4 2.8 4.5 3.0 2.2 3.5 3.1* 3.2 2.2 1.0 -- 3.3 3.2 4.1 3.3 2.7 2.8 3.1 2.5 2.7 4.3 3.1 2.3 3.4 3.0* 3.1 5.4 2.5 -- 2.8* 3.0 3.4 3.1 2.6 2.5 2.8 2.4 2.5 3.5 3.0 2.2 3.0 2.8* 2.8 -- 4.0 -- 2.7 2.8 2.9 2.8 2.5 2.1 2.3 2.2 2.2 2.9 2.8 2.1 2.5 2.5* 2.5 0.0 7.5 -- 2.8 2.8 2.7 2.8 2.6 2.3 2.4 2.4 2.3 2.5 2.9 2.3 2.4 2.5* 2.5 0.0 10.0 -- 2.5 2.5 2.4 2.6 2.4* 2.3 2.3 2.1 2.1 2.1 2.5 2.2 2.2 2.3* 2.3 0.0 12.5 -- 2.4 2.4 2.4 2.4 2.4 2.1 2.1 2.2 2.2 2.3 2.5 2.4 2.3 2.3* 2.3 0.0 15.0 -- 2.3 2.4 2.4 2.4 2.4 2.2 2.2 2.1 2.1 2.1 2.3 2.2 2.1 2.2* 2.2 0.0 20.0 -- 2.4 2.4 2.5 2.4 2.4 2.4* 2.4* 2.4 2.4 2.4 2.4* 2.6 2.4 2.4* 2.4 0.0 60.0 -- 2.4 2.4 2.4 2.4 2.4 2.4 2.4 2.6 2.6 2.6 2.6 2.6 2.6 2.6* 2.5 0.0 CM 0.05 -- -- 1.2 2.6 1.4 2.2 1.5 1.2 2.7 3.0 2.8 1.2 2.4 2.4 -- 2.0 65.9 0.2 -- -- -- -- -- -- 1.1 -- 2.0 2.2 2.4 0.8 2.2 1.8 -- 1.8 -- 0.5 -- -- 1.2 2.3 1.4 2.0 1.4 0.8 2.0 2.2 2.7 1.0 2.0 1.8 -- 1.7 6.0 CV 0.05 -- -- -- 1.2 0.6 0.2 -0.1 0.9 -0.2 -0.2 0.7 0.1 -0.3 2.1 1.4 0.5 32.2 0.2 -1.0 -- -0.1 1.4 0.7 0.6 0.1 1.0 -0.2 -0.4 0.6 0.2 -0.1 1.9 1.2 0.4 2.8 0.5 -1.4 0.9 -- -- 0.4 0.3 -0.2 0.8 -0.2 -0.4 0.4 0.1 -0.3 1.8 1.2 0.3 1.4 1.0 -- 0.6 -0.4 0.5 -0.3 -- -0.9 0.2 0.6 -- 0.2 -0.2 -0.9 1.4 0.7 0.1 2.0 1.5 -2.8 -0.7 -- -- -1.5 -- -1.7 -0.6 -0.5 -0.5 -0.6 -- -1.6 0.2 -3.0 -1.0 14.8 RS 0.02 -- -- -- -- -- 3.3 3.6 3.4 3.2 3.7 3.6* 2.9 3.3 -- -- 3.4 17.9 0.1 -- -- -- -- -- 3.4* 3.7 3.7 3.2 3.6 3.5 2.7 3.0 -- -- 3.3 5.9 0.2 -- -- -- -- -- 3.4 3.6 3.8 3.3 3.6 3.7 3.1 3.5 -- -- 3.5 11.6 0.5 -- -- -- -- -- 3.4 3.6 3.8 3.1 3.2 3.6 3.3 3.6 -- -- 3.4 13.0 1.0 -- -- -- -- -- 3.9 4.1 4.1 3.6 3.4 4.0 3.5 3.9 -- -- 3.8 0.0 SJ 0.02 -- -- 4.0 3.0* 2.7 2.5 2.2 3.7 2.7 3.0 3.2 -- -- -- -- 3.0 20.3 0.1 -- -- 2.7 3.3* 3.0 3.2 2.8 3.8 3.3 3.6 3.7 -- -- -- -- 3.3 8.1 0.2 -- -- 3.2 4.3 4.3 4.2 3.2 4.6 3.7 4.1 1.9 -- -- -- -- 3.7 4.4 0.5 -- -- 3.3 3.8 4.6 3.8 3.1 3.9 3.1 3.4 1.7 -- -- -- -- 3.4 2.4 1.0 -- -- 3.9 4.1 4.5 3.8 3.9* 4.1 3.3 3.5 4.4 -- -- -- -- 3.9 2.8 678 679 680 -- No data. 681 * Value obtained from interpolation due to the lack of data for some months. 682 Page 24 of 32 http://mc.manuscriptcentral.com/ppp Permafrost and Periglacial Processes 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 For Peer Review 684 Table 3. Monitoring of rock glacier dynamics from 2001 to 2016, including the subsidence 685 and advances of this landform, together with an estimation of the loss of volume of the 686 frozen body above which the rock glacier sits, as well as the percentage of snow cover 687 present across the Veleta cirque floor by late August. 688 Study period (from September to August) Snow cover in summer (%) Subsidence (m) Advance (m) Volume loss (m3) 2001-2002 <5 -0.203 0.083 774.1 2002-2003 >10 -0.283 0.115 1079.6 2003-2004 >50 -0.103 0.039 392.9 2004-2005 0 -0.651 0.200 2483.5 2005-2006 0 -0.414 0.145 1579.4 2006-2007 0 -0.401 0.164 1529.8 2007-2008 0 -0.391 0.095 1491.6 2008-2009 <15 -0.240 0.064 915.6 2009-2010 100 -- -- -- 2010-2011 100 -- -- -- 2011-2012* <10 -0.279 0.105 1064.3 2012-2013 95 -- -- -- 2013-2014** <10 -0.198 0.063 755.3 2014-2016 0 -0.805 0.172 3071.0 Total - -3.968 1.245 15137.4 689 690 -- No data. 691 * Includes data from late August 2009 to late August 2012. 692 ** Includes data from late August 2012 to late August 2014. Page 25 of 32 http://mc.manuscriptcentral.com/ppp Permafrost and Periglacial Processes 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 For Peer Review 694 Figure captions 695 Figure 1. Location of the massif of Sierra Nevada in Europe, together with a sketch with the distribution of 696 the different monitoring sites. 697 Figure 2. Pictures of the different monitoring sites examined in the text. 698 Figure 3. Evolution of (a) air temperatures at the Veleta peak, together with soil temperatures at: (b) the 699 Veleta bedrock, (c) sorted-circle of the Machos summit plateau, and (d) rock glacier of the Veleta cirque 700 floor. 701 Figure 4. (a) Movement and direction of single monitored stakes based on total station measurements (2002- 702 2016), (b) subsidence of the surface of the rock glacier from 2012 to 2016 based on laser scanning (2002- 703 2016), (c) evolution of the elevation of the monitoring stakes along the transect from A to B using high 704 resolution Global Positioning System data (2004-2016). 705 Figure 5. Comparison between snow cover distribution in the Veleta cirque floor in late August of the dry 706 year 2006 (above) and of the snowy one in 2010 (below). On the left side, there are pictures of the area (the 707 red circle represents the location of the rock glacier), and on the right side there is the geomorphological 708 sketch of the cirque floor with the distribution of snow cover. 709 Figure 6. Evolution of (a) air temperatures at the Veleta peak, together with soil temperatures in solifluction 710 lobes located in the: (b) Rio Seco cirque, and (c) San Juan valley. 711 Page 26 of 32 http://mc.manuscriptcentral.com/ppp Permafrost and Periglacial Processes 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 For Peer Review Figure 1. Location of the massif of Sierra Nevada in Europe, together with a sketch with the distribution of the different monitoring sites. Page 27 of 32 http://mc.manuscriptcentral.com/ppp Permafrost and Periglacial Processes 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 For Peer Review Figure 2. Pictures of the different monitoring sites examined in the text. Page 28 of 32 http://mc.manuscriptcentral.com/ppp Permafrost and Periglacial Processes 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 For Peer Review Figure 3. Evolution of (a) air temperatures at the Veleta peak, together with soil temperatures at: (b) the Veleta bedrock, (c) sorted-circle of the Machos summit plateau, and (d) rock glacier of the Veleta cirque floor. 849x525mm (96 x 96 DPI) Page 29 of 32 http://mc.manuscriptcentral.com/ppp Permafrost and Periglacial Processes 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 For Peer Review Figure 4. (a) Movement and direction of single monitored stakes based on total station measurements (2002-2016), (b) subsidence of the surface of the rock glacier from 2012 to 2016 based on laser scanning (2002-2016), (c) evolution of the elevation of the monitoring stakes along the transect from A to B using high resolution Global Positioning System data (2004-2016). Page 30 of 32 http://mc.manuscriptcentral.com/ppp Permafrost and Periglacial Processes 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 For Peer Review Figure 5. Comparison between snow cover distribution in the Veleta cirque floor in late August of the dry year 2006 (above) and of the snowy one in 2010 (below). On the left side, there are pictures of the area (the red circle represents the location of the rock glacier), and on the right side there is the geomorphological sketch of the cirque floor with the distribution of snow cover. 206x168mm (600 x 600 DPI) Page 31 of 32 http://mc.manuscriptcentral.com/ppp Permafrost and Periglacial Processes 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 For Peer Review Figure 6. Evolution of (a) air temperatures at the Veleta peak, together with soil temperatures in solifluction lobes located in the: (b) Rio Seco cirque, and (c) San Juan valley. 728x325mm (96 x 96 DPI) Page 32 of 32 http://mc.manuscriptcentral.com/ppp Permafrost and Periglacial Processes 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60