Lateglacial and Holocene Evolution of Glaciers and Permafrost in the Val Muragl, Upper Engadin, Swiss Alps
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Permafrost, Phillips, Springman & Arenson (eds) © 2003 Swets & Zeitlinger, Lisse, ISBN 90 5809 582 7 Lateglacial and Holocene evolution of glaciers and permafrost in the Val Muragl, Upper Engadin, Swiss Alps M. Maisch, W. Haeberli, R. Frauenfelder, A. Kääb Glaciology and Geomorphodynamics Group, Geography Department, University of Zurich, Switzerland C. Rothenbühler Academia Engiadina, Samedan, Switzerland ABSTRACT: Spectacular landforms associated with permafrost creep and glacier fluctuations characterize the Val Muragl, one of the most frequently visited high-mountain valleys and tourist attractions in the St. Moritz area, Upper Engadin, eastern Swiss Alps. Combined consideration of glaciers and permafrost enhances the possibili- ties of understanding the landscape evolution in this area. The Val Muragl is able to constitute a large and easily accessible “geotope-site” illustrating phenomena and processes of Lateglacial, Holocene and present-day time scales. The scientific vision is based on a variety of methodological approaches such as GIS-based geomorpho- logical mapping, reconstruction of Lateglacial and Holocene palaeoglaciers, field mapping and spatial modelling of permafrost occurrences, photogrammetric analyses, relative age dating using the Schmidt–Hammer technique, geophysical soundings, drilling and borehole investigations. The landscape evolution starts from a situation with a cold or polythermal accumulation area, covering most of the topography during full Ice-Age conditions, and leads to Lateglacial retreat stages of polythermal valley glaciers surrounded by permafrost. The Holocene situa- tion displays repeated but spatially limited glacier advances accompanied by the development of large sediment bodies partially subjected to permafrost creep and the present-day situation is characterized by ongoing vanish- ing of the remaining surface ice as well as by complex patterns of de- and aggrading periglacial permafrost. 1 INTRODUCTION of a 20,000-year landscape evolution with quite dra- matic changes. As a consequence, Val Muragl has an Present-day landforms in cold mountain areas are important potential to be declared a protected site of strongly influenced by their development since full high value for geoscience and landscape or a so-called Ice-Age conditions (Florineth 1998) via Lateglacial ice “geotope”. The following briefly outlines the main disappearance to Holocene ice fluctuations and 20th aspects to be considered in this context, i.e. the scien- century warming trends (Maisch 2001). Under condi- tific background and the evaluation of the interest tions of a climate which is transitional between from the side of the public – a true transdisciplinary wet-maritime conditions at humid margins of coastal task of glacier and permafrost research. mountains and dry continental regimes found in many mountain chains at greater distance to oceanic sources, annual precipitation is generally around 1000 mm 2 GEOMORPHOLOGY OF VAL MURAGL at timberline and polythermal glaciers coexist with periglacial permafrost in close neighbourhood (Haeberli Geomorphology, as a specialized and meanwhile 1983, Kneisel 1999, Kneisel et al. 2000). Thorough highly computerized discipline of earth science and in understanding of landscape evolution must, therefore, combination with the topographic, geological, hydro- be based on a combined consideration of both types of logical and glaciological background provides one of perennial ice occurrences and their various but still the most important “information layers” for multidis- hardly investigated interactions through time. ciplinary landscape analysis, its interpretation and The Val Muragl in the Upper Engadin, eastern visualisation (Fig. 1). Swiss Alps, has not only been a focus of correspon- In high-alpine environments such as the Bernina ding research for years now but also represents one of region and its adjacent valleys, most geomorphic the major attractions within the spectacular and processes are evidently dynamic; on the “macro-”, world-famous tourist region around St. Moritz and “meso-” and “micro-scale” level, they are strongly Pontresina. This means that a great number of hikers linked to numerous other natural phenomena such as visit an area with extraordinarily well developed permafrost distribution, soil development and vegeta- “text-book” examples of typical high-mountain land- tion cover (cf. glaciological map of Julier-Bernina; NFP forms, enabling a deep understanding of glacial as 31 1998; cf. Haeberli et al. 1999). Geomorphological well as periglacial processes and a fascinating vision aspects serve also as modern guidelines for specific 717 Figure 1. 3D-view of the Bernina region with Val Muragl in the center. Satellite imagery ©ESA/Eurimage 1990–1994. Image processing by Dr. Urs Frei, Remote Sensing Laborato- ries RSL, Geography Department. University of Zurich. public and tourism-related educational concepts of landscape didactics (WWF Switzerland & Natf. Gesel- lschaft Engadin, 1998: “Climate trail Pontresina/ Muragl”; Maisch et al. 1999: “Glacierforefield trail Morteratsch”). Figure 2. Section (appr. 5 ϫ 3 km) of the geomorpholog- The geomorphology of the Val Muragl and the adja- ical map of Val Muragl and Val Champagna (Rothenbühler cent areas of Val Champagna, Val Languard and Val 2000, simplified legend in German). Roseg, was recently mapped, accomplished with a new GIS-based approach, described and analyzed (Rothenbühler 2000) as a mosaic-like part of an extended mapping project on the geomorphology of the entire northern Swiss part of the Bernina massif (Maggetti 1994, Vogel 1995, Castelli 2000, Koch in prep.). A small section of the geomorphologic cartog- raphy of the inner Val Muragl is illustrated in Figure 2. The mapping procedure applied here followed the “GMK 25-concept” (Leser & Stäblein 1975, Schoeneich 1993, cf. also Kneisel et al. 1998). The concept divides the landforms and the associated processes (in a simplified way) into different process units (glacial, periglacial, fluvial, gravitational, denuda- tional, biotic/organic and anthropogenic) according to Figure 3. Oblique low angle view of the upper part of their predominance represented by a standardized Val Muragl with the most pronounced landforms indicated colour system. In the order of significance, gravita- (Photography: Chr. Rothenbühler, 2000). tional (rock falls from headwalls at high altitudes), denudational (valley slopes in general without clearly developed landforms), glacial (morainic ridges of debris flow channels depositing debris fans at the foot- lateglacial or holocene age, glacier forefields, ice- zone of the slopes especially in the Val Champagna. marginal terraces) and periglacial zones (rockglaciers, protalus ramparts) are the most frequent geomorpho- 3 FULL ICE AGE CONDITIONS logic units found in Val Muragl with respect to their spatial distribution and importance in recent geomor- During maximum glaciation (around 20 ka BP). Val phologic activity (Fig. 3). Muragl and the entire region of the Upper Engadin Fluvial processes (debris flows and alluvial fans) are was part of a major centre and dome within the accu- mirrored by a large number of erosional scars and mulation zone of the Ice-Age glaciers, receiving their 718 a) Longitudinal valley profile precipitation predominantly from mediterranean Piz Bernina actual glacier size 4049 m sources in the south and flowing radially out to vari- Val Champagna Val Muragl ous directions (Florineth 1998). Only ridges above 1850 Val Languard Berninapass about 2,600 to 3,000 m a.s.l. stuck out of the firn Margun 1850 Punt Muragl Pontre- surface which may have been cold with mean annual sina MorteratschRoseg firn temperatures around Ϫ15 to Ϫ20°C (Blatter & Cinuos-chel Samedan Haeberli 1984). Deep penetration of subglacial per- mafrost, especially on valley slopes, and of continu- b)Time/space-diagram of the glacier front position ous mountain permafrost on ice-free ridges and (Roseg/Tschierva and Morteratsch glacier) glaciers summits must be assumed. However, polishing and glacier advance today period 1850of striations of high-altitude bedrock (on the rounded Holocene advance real distance periods not to scale crest between Val Muragl and Val Champagna, for stadial of of glacier as small Pontresina as in 1850 Holocene instance) indicates that temperate basal conditions (ca. 11’000 y BP) 10000 y BP stadial of must have existed in the glaciers during earlier and Samedan stadial of (ca. 13’000 y BP) E ? M I Cinuos-che TIMET later stages of ice build-up and vanishing. This leaves (ca. 14’000 y BP) important questions concerning the timing, duration ? glacier front retreat ? and maximum depth of subglacial permafrost forma- position unknown Lateglacial period tion open and indicates high complexity of spatio- LGM last glacial maximum 20000 y BP temporal permafrost development at depth. SPACESPACE end moraine series glacier advance periods glacier front position ("stadials", cool phases) estimated ages 14C-years BP glacier retreat periods y BP (before present, uncalibrated) ("interstadials", warm phases) reconstructed variations of 4 LATEGLACIAL EVOLUTION villages the glacier front position The Lateglacial decay of surface ice (20,000-10,000 y Figure 4. Generalized system of late-würmian glacier retreat, adapted for the Bernina region. a) longitudinal valley BP, uncalibr.) in and around the Bernina region profile stretching from the stadial of Cinuos-chel up to the formed noticeable morainic systems near Cinuos-chel recent glaciers