Nuria Andrés

Distribution and effectiveness of nivation in Mediterranean mountains: Peñalara (Spain)

Abstract Snow accumulation is responsible for geomorphic and biogeographic processes taking place in the southern sector of the Penalara massif in central Spain (40°51′N, 3°57′W; max. altitude 2428 m at Pico de Penalara). This work compares the intensity of nivation on the eastern slope, leeward of the prevailing westerly winds and heavily eroded by glacial activity during the Pleistocene, to that of the western slope on the windward side, unaffected by glacial erosion and completely covered by a thick weathering mantle. On the eastern slope, nivation is effective only where the weathering mantle is exposed or on morainic formations. It does not occur on the landforms derived from glacial erosion. In contrast, the western side shows almost no evidence of snow action except where catastrophic mass movements have altered the regularity of the slope. During the post-glacial epoch, nivation cirques formed in the scars left by mass wasting. In the last 30 years, spring temperatures have increased and this activity has diminished. The pattern of evolution observed at Penalara can be extrapolated to other Mediterranean mountains with similar characteristics such as marginal glacial activity during the Pleistocene, unconsolidated formations on the summits caused by chemical weathering, and dry, hot summers that can increase the effectiveness of nivation.

Holocene and ‘Little Ice Age’ glacial activity in the Marboré Cirque, Monte Perdido Massif, Central Spanish Pyrenees

The Marboré Cirque, which is located in the southern Central Pyrenees on the north face of the Monte Perdido Peak (42°40′0″N; 0.5°0″W; 3355 m), contains a wide variety of Holocene glacial and periglacial deposits, and those from the ‘Little Ice Age’ (‘LIA’) are particularly well developed. Based on geomorphological mapping, cosmogenic exposure dating and previous studies of lacustrine sediment cores, the different deposits were dated and a sequence of geomorphological and paleoenvironmental events was established as follows: (1) The Marboré Cirque was at least partially deglaciated before 12.7 kyr BP. (2) Some ice masses are likely to have persisted in the Early Holocene, although their moraines were destroyed by the advance of glaciers during the Mid Holocene and ‘LIA’. (3) A glacial expansion occurred during the Mid Holocene (5.1 ± 0.1 kyr), represented by a large push moraine that enclosed a unique ice mass at the foot of the Monte Perdido Massif. (4) A melting phase occurred at approximately 3.4 ± 0.2 and 2.5 ± 0.1 kyr (Bronze/Iron Ages) after one of the most important glacial advances of the Neoglacial period. (5) Another glacial expansion occurred during the Dark Age Cold Period (1.4–1.2 kyr), followed by a melting period during the Medieval Climate Anomaly. (6) The ‘LIA’ represented a clear stage of glacial expansion within the Marboré Cirque. Two different pulses of glaciation were detected, separated by a short retraction. The first pulse occurred most likely during the late 17th century or early 18th century (Maunder Minimum), whereas the second occurred between 1790 and ad 1830 (Dalton Minimum). A strong deglaciation process has affected the Marboré Cirque glaciers since the middle of the 19th century. (7) A large rock avalanche occurred during the Mid Holocene, leaving a chaotic deposit that was previously considered to be a Late Glacial moraine.

Glacier retreat during the recent eruptive period of Popocaté petl volcano, Mexico

Abstract Popocatépetl (19°02’ N, 98°62’W; 5424 m) is one of the largest active stratovolcanoes in the Transmexican Volcanic Belt. A glacier located on the north side has undergone severe ablation since the volcano reinitiated eruptive activity in December 1994. In our study, we calculate the extent of the glacier recession and the loss in glacial mass balance during the period of greatest laharic activity (1994–2002), using photogrammetric treatment of 20 pairs of aerial photographs. The results indicate that from November 1997 to December 2002, the glacier released approximately 3 967 000 m3 of water. A period of intense glacier melting occurred from 4 November 2000 to 15 March 2001 during which time 717 000 m3 of water was released. Much of the melting was attributed to the pyroclastic flow that took place on 22 January 2001 and produced a 14.2 km lahar with 68 000 m3 of water. Among the many types of volcanic events, pyroclastic flows were the most effective in causing sudden snowmelt, although small explosions were also effective since they deposited incandescent material on the glacier. The collapse of the plinian columns covered the glacier with pyroclasts and increased its volume. The existence of control points for georeferencing and a knowledge of the topography underlying the glacier previous to the eruption would have provided more accurate and useful results for hazard prevention.

Evidence of glacial activity during the Oldest Dryas in the mountains of Spain

Abstract In this review, recently published results of cosmogenic dating of moraine boulders, rock glaciers and glacially-polished surfaces in various mountain massifs (the Sierra Nevada, the Central Range, the Pyrenees and the Northwestern Mountains) of the Iberian Peninsula were analysed to assess the importance of the glacial advance and subsequent retreat that occurred during the Oldest Dryas, between 17.5 and 14.5 ka. The glaciers, which had almost disappeared at the beginning of this period (approximately 17.5 ka), returned to fill the valley floors at approximately 16.8–16.5 ka, depositing moraines close to the moraines generated during the Last Glacial Maximum advance. Following this intense and short advance, the glaciers began to retreat, although this was frequently interrupted by glacial readvance episodes, with the last occurring at approximately 15.5 ka. Subsequently, the retreat was generalized, so that 1 ka later the glaciers were restricted to the cirque areas, and never again advanced. During this recession, the activity of many of the deglaciated cirque walls triggered frequent rockfalls, transforming the retreating degraded glaciers into rock glaciers; their fronts had become inactive by approximately 14 ka, although in many cases their roots conserved the internal ice until well into the Holocene. The glacial fluctuations, and the landforms and deposits consequently derived from them, are very similar to those described for other Mediterranean and European mountain ranges, especially the Alps. We conclude that the climate changes associated with the Oldest Dryas, had important impacts on mountain landscapes throughout the continent.

High sensitivity of North Iceland (Tröllaskagi) debris-free glaciers to climatic change from the ‘Little Ice Age’ to the present:

The Tröllaskagi peninsula is located in northern Iceland, between meridian 19°30′W and 18°10′W, jutting out into the North Atlantic to latitude 66°12′N. The aim of this research is to study recent glacier changes in relation to climatic evolution of the Gljúfurárjökull and Tungnahryggsjökull debris-free valley glaciers in Tröllaskagi. Glacier extent mapping and spatial analysis operations were performed with ArcGIS (ESRI), using analysis of aerial photographs from 1946, 1985, 1994 and 2000, and a 2005 SPOT satellite image. The results show that these glaciers lost a quarter of their surface area between the ‘Little Ice Age’ and 2005. In this paper, the term ‘Little Ice Age’ follows Grove (2001) as the most recent period when glaciers extended globally between the medieval period and the early 20th century. The abrupt climatic transition of the early 20th century and the 25-year warm period 1925–1950 triggered the main retreat and volume loss of these glaciers since the end of the ‘Little Ice Age’. Meanwhile, cooling during the 1960s, 1970s and 1980s altered the trend, with advances of the glacier snouts. Between the ‘Little Ice Age’ and the present day, the mean annual air temperature and mean ablation season air temperature increased by 1.9°C and 1.5°C, respectively, leading to a 40–50 m rise in the equilibrium line altitude (ELA) of the glaciers during this period. The response of these glaciers depends not only on the mean ablation season air temperature evolution but also on other factors such as winter precipitation. The models applied show a precipitation increase of up to more than 700 mm since the ‘Little Ice Age’.

GROUND THERMAL CONDITIONS AT CHACHANI VOLCANO, SOUTHERN PERU

Andrés, N., Palacios, D., Úbeda, J. and Alcalá, J., 2010. Ground thermal conditions at Chachani volcano, Southern Peru. Geografiska Annaler: Series A, Physical Geography, 93, 151–162. DOI: 10.1111/j.1468‐0459.2011.00424.x Abstract Shallow ground temperatures were measured and periglacial and permafrost environments identified at the Chachani volcanic complex in the west‐central Andes in southern Peru (16° 11′ S; 71° 31′ W, elevation 6057 m a.s.l.). Three stations were installed at 4850, 4976 and 5331 m a.s.l. on the southern slope and the data were processed to produce ground temperature distribution models at depth and altitude. Snow cover lasts only a few days each year. Air and ground surface temperatures oscillate around 0°C almost daily, but the temperature is stabilized only a few centimetres below the ground surface. The lower limit of thermal conditions for isolated patches of permafrost occurs at 5050 m on the south‐facing slopes. Thermal conditions associated with discontinuous permafrost occur from 5250 to 5420 m a.s.l., with continuous permafrost found above this level. The permafrost distribution models show that the rock glaciers observed on the southern slopes of the complex are within the active permafrost zone.

Unchanged surface morphology in debris-covered glaciers and rock glaciers in Tröllaskagi peninsula (northern Iceland)

Abstract This paper analyses changes in the surface morphology of rock and debris-covered glaciers in the Holadalsjokull and Fremri-Grjotardalur cirques near Holar village in the Trollaskagi peninsula (northern Iceland) (65°43′55″N; 19°06′49″W, 160 m), to understand the dynamics and climatic significance of these landforms. The study includes an analysis of historical aerial photographs from 1946 to 2000. The aim was to evaluate surface changes in these landforms and obtain the horizontal displacement and elevation changes of large boulders and linear features (ridges and furrows) at each date. In addition, the surface elevation differences between 1980 and 1994 were obtained from digital elevation models. The horizontal displacement results obtain a mean velocity of 0.33 m yr−1 and an average elevation difference of −0.72 m for the boulders, with the linear features advancing 14.84 m during the period 1946–2000. Except for this slow mobility, no changes occurred in the surface morphology of these landforms during the 54 years. The low displacement rates of boulders and linear features, together with the surface lowering processes observed in these landforms, indicate that widespread melting is the most important activity in the debris-covered and rock glaciers in Trollaskagi. This is confirmed by the recent formation of collapse depressions.