New advances in the study of Alpine glaciations

ShangZhe Zhou

School of Geography, South China Normal University, Guangzhou, Guangdong 510631, China

1 Introduction

The 18th INQUA (International Union for Quaternary Research) was held on July 21–27, 2011 in Bern, Switzerland. More than 3,400 people attended the conference. The Quaternary glaciations has always been one of the hottest issues of INQUA and field investigations focused on such issue were organized before, during and after the conference. Alps is the place where Agassiz initially did his research on glacier and established the glaciology in the early 19th century (Agassiz, 1837, 1840). It is also the place where Penck studied Quaternary glacier and founded the classic mode of four glaciations in the beginning of 20th century (Penck and Brückner, 1909). For more than one hundred years, scientists never ceased to study on Quaternary glacier of Alps, especially based on the great breakthrough on chronology methods in recent year, researches on glaciations since the Last Glaciation have made numerous progresses. Luckily,the author participated in the mid-congress excursion for one day and the post-congress excursion for five days. The mid-congress excursion was organized by Professor Naki Akcar and Dr. Corinne Blum, which focused on pre-LGM (Last Glaciation Maximum) and LGM paleoglacier records of the Northern Alpine Foreland. The post-congress excursion was organized by professors, Jurgen Reitner from Austria Geological Survey (Osterreichisches Geologisches Bundesamt),Markus Fiebig from Vienna University of Natural Resources and Application Life Sciences, Susan Ivy-Ochs from the Geography Department of Zurich University, and Max Maisch from the Geography Institute of Zurich University. Additionally, professors Christoph Spotl, Harms Kerschner and Marc Ostermmn from the Innsbruck University of Austria par-ticipated in the field introductions. The post-congress excursion focused on Alpine glaciations and the Inn glacier system. The Alps is the birthplace of glaciology theory and a core region for studying alpine glaciations,thus is a significant reference point for glaciological studies in the Tibetan Plateau. With an intention to benefit the studies in the Tibetan Plateau, this article will introduce certain research achievements and progresses on Alps area upon the combination of some relevant publications.

2 Research on older glaciations

The Alps is the largest and highest mountain in Europe (Figure 1), located in southern Europe and extends across France, Italy, Switzerland, Germany and Austria. Its length is 1,200 km, width 130–260 km,average elevation about 3,000 m, and total area about 2.2×105km2. The main peak, Mount Blanc reaches to an elevation of 4,810 m. There are more than 1,200 modern glaciers in the Alps with a modern snowline elevation of about 2,500 m. The longest glacier Aletsch is 22.5 km. In southern Germany, glacial landforms and sediments are relatively complete, and the area is divided into three regions by river systems:the Rhine drainage basin in the west, the Danube drainage basin in the middle, and the Inn River drainage basin in the east. Quaternary glaciation remnants are most outstanding in the S–N direction tributary valleys of the Danube Basin.

Figure 1 The Alps Mountains (Source: http://gs.riverdale.k12.or.us/~suzannal17/swiss/)

The Publication ofDie Alpen im eiszeitalter(Penck and Brückner, 1909) is considered as a seminal work in the Alps Quaternary glacier research, and the information provided is widely accepted by academia(Fiebiget al., 2004). Penck and Brückner confirmed four deckenschotters of southern Germany: Older Deckenschotter, Younger Deckenschotter, High Terrace, and Lower Terrace, and some relative evidences of rocks, paleosols, geomorphology and stratigraphy.Based on the consideration that the deckenschotter will accumulate during the glacial period and be incised during the interglacial period, Penck and Brückner(1909) founded the theory of four glaciations. The four glaciations, named after four rivers on the northern slope of the Alps in the southern Germany are Günz,Mindel, Riss and Würm. Impressively, the initials of these four names are arranged next to each other in alphabetical order, so that it could facilitate people to memorize its sequences. Due to the strong evidences and convincing demonstration, Penck’s viewpoint had been widely accepted by the academia and honored as the classic Alps Quaternary glacial mode.

Eberl (1930) discovered a higher and older Deckenschotter, thus he added Donau glaciation before Günz. Schaefer (1956) confirmed the existence of Donau, yet he distinguished another terrace gravel layer from Donau, which is named by him the Biber glaciation. Shaefer labeled Donau as Lower Deckenschotter and Biber as Upper Deckenschotter.Schreiner and Ebel (1981) found an extra Middle Deckenschotter distinct from Penck and Brückner’s Younger Deckenschotter in the Ulm region, meaning that another glaciation was present before Mindel glaciation. Until now the Pleistocene Deckenschotter of Alps has amounted to seven, the order from old to young is classified in table 1. These first letters of the glaciations follows the alphabetical order (Fiebiget al.,2004).

Table 1 Pleistocene glaciations and their evidence

Ellwangeret al.(1995) found another Pleistocene Deckenschotter in the center area of the Rhine glacier.They noted there should be three glaciations after Mindel, but this discovery has not been reconfirmed.

The aforementioned is a brief introduction to research achievements of Pleistocene glaciation sequence in the Alps region. Now it is necessary to explain why the researchers rely on Deckenschotters rather than moraines to confirm glaciations. The reason is that the glacier of the area during the LGM was so extensive (reached an area of 2×105km2and a thickness of 1 km) so that the earlier moraines were nearly destroyed; as a result, the remaining fluvioglacial gravels, the deckenschotters spread out into the periphery region of the glaciers, which is the significant evidences of glaciations. Fluvioglacial sediment is formed by glacier melt water. In order to distinguish deckenschotter in the river valley from normal river sediment, we need to find differences on sedimentary facies. Deckenschotter presents numerous special features, including on sorting degree, psephicity and gravel morphology; A critical sign is that it contains striated stones that have not been totally remolded by water transportation, as they were not carried a very long distance. The glacial period is also the time when outwash plain and valley gravels accumulated.Therefore, Penck and Brückner (1909) took the glaciofluvial terrace as evidence of a glacier period. In the mountain areas, deckenschotters was shown to be terraces sequences, while in the piedmont, deckenschotters were aggraded discontinuously from old to young (Figure 2).

Figure 2 Glaciofluvial gravels (left) and the explanations on field board (right) at the south of Munich Plain, northern Alps

After glaciation order was established, dating became a key problem. In 1924, Milankovitch worked out the summer half-year solar radiation curve during the past 600,000 years based on the earth’s orbital parameters. K?ppen and Wegener established a relation between nine valleys of the curve and Penk and Brückner’s four glaciations and suggested a theoretical beginning time of the four glacier periods. Therefore, academia once regarded the four glaciations after Günz as the events occurring during the 600,000 years. However, a more accurate time frame of when the glaciations began is required. In 1994–1995, Ellwangeret al. (1994), Bludau (1995),R?hl?e (1995), Strattner and Rolf (1995) carried out many surveys on sediment in west to Augsburg in the south of Germany. They found a 2-m-thick fine-grained layer containingArvicola’s teeth and mollusca fossils on top of Lower Deckenschotter; the 2-m-thick fine-grained layer was overlaid by another peat layer containingAlnus-Tsuga-Pinuspolen sequence; within the top 3 m, the grain size changed upward from fine to coarse, and there was a paleomagnetic reversal event. Research on this biologic-paleomagnetic sediment shows that the Donua glaciation represented by the Lower Deckschotter should occurred between the Pliocene and Pleistocene. For Günz-Mindel glaciations, it was once believed that the Older Deckenschotter belonged to the Brunhes/Matuyama magnetic boundaries in terms of tectonics-stratigraphy. Later, researchers found evidences of paleomagnetic reversal events from the diamicton deposit under the Middle Deckenschotter and lenticles at the bottom of the Younger Deckenschotter. Finally, whether the three Deckenschotters represent three different glaciations or belong to the same period is still in doubt.

Large erratics were found at Montoz next to the Bielersee Lake in northwestern Switzerland and its area exceeded the distribution extent in the Last Glaciation. The dating of cosmogenic nuclide from these erratics are between 128–184 ka, showing those erratics belong to MIS-6. Thus, Penck and Brückner’s opinion about Riss was convinced (Grafet al., 2007).

As for the interglacial, the traditional opinion after Penck and Brückner was that, there was a great interglacial period between Younger Deckenschotter and High Terrance. Actually, it is considered at present there may be three interglacial periods. Ellwangeret al.(1995) thought there was at least one glaciation between Mindel and Riss, and the evidences for the interglacial between these older glaciations are not abundant. However, some best pollen records for the Last Interglacial were discovered at Samerberg in the Inn River Valley of Bavaria, south Germany. Three subsequent interstadials were clearly recognized in these records and the content of pine pollen was very high. Similar profiles were found at a tongue-shaped ice eroded basin, Wurzacher Bechen, formed by Riss glaciation in the Rhine glacial region. Obviously, this interglacial could compare with the Eemian interglacial (MIS-5). The three interstadials could undoubtedly reflect the 5e, 5c, and 5a stages, and since then the Last Glaciation started.

The most typical Quaternary glacial remnants at the southern slope of the Alps in Italian are distributed in the Garda Lake area. These glacial deposits include the Solferino moraine (Late Pleistocene), Sedena moraine (Late-Middle Pleistocene), Carpoenedolo moraine (Middle Pleistocene), Monte Faita moraine(Middle-Early Pleistocene) and Ciliverghe moraine(Early Pleistocene). Among them, the Ciliverghe moraine has the maximum glaciation scale. The Solferino moraine was determined as the results of the Last Glaciation, while the other four lack sufficient dating data, and the deposition relationship between them is still controversial (Castiglioni, 2004).

3 Research on glacier change since the Last Glaciation

Glaciers in the Alps were very large during the LGM and formed an ice sheet with an area of 2.2×105km2, nearly covering all of Switzerland, and parts of Germany, Austria, Italia and France (Figure 3). The northeast side of this sheet was 200–300 km away from the Nordic ice sheet.

Figure 3 The ice sheet extent of the Alps during LGM (Ivy-Ochs et al., 2006). Red line is the boundary of LGM ice sheet; circles are the studied sites: M—Montoz; S—Solothurn; Gr—Grimsel Pass; A—Grosser Aletsch Glacier; J—Julier Pass;K—Kromer, Kartell and Schonferwall; Gz—Trins Gschnitz moraine

Areas where cities now stand such as Geneva, Bern,Zurich, Lucerne and Innsbruck were all buried under this ice sheet then. At that time the equilibrium line altitude (ELA) was 1,200–1,500 m lower than that at present. The Rhone Glacier passed Grimsel Pass and flowed into the Aare Valley and reached down into the nearby regions of the Wangen Town, 30 km north of Bern, remaining numerous large big boulders. This ice sheet not only destroyed previous landforms of the entire Alps, but also destroyed earlier glacial deposits.Thus, researches are only left with fluvioglacial terraces in the valleys and the outwash sediments in the piedmont to reconstruct the history of early glaciations.As the glacial advance scales after LGM became smaller, the moraines in the valleys remained orderly.There are numerous beautiful lakes scattered in the Alps regions, most of which are glacial lakes formed during or after the Last Glaciation, such as Lake Geneva in western Switzerland, Lake Neuchatel, Lake Bodensee on the border of Germany and Switzerland,and Lake Garda on the border of Switzerland and Italy.In recent years, European colleagues have reconstructed the glacial history of many typical valleys since the MIS-2 stage by making use of the advanced cosmogenic nuclide (10Be,21Ne,26Al,36Cl) dating method, revealing numerous climate events in the Alps(Ivy-Ochset al, 2006), and the following are several principals.

The glaciers in LGM extended to the piedmont areas at about 30 ka B.P., reaching a maximum at about 21.0±0.9 ka B.P. and then retreated. The relating evidences are that the10Be,26Al,36Cl dating ages of the four boulders near the Wangen city are from 17,070±720 a B.P. to 21,050±860 a B.P..

The glaciers advanced again at 16 ka B.P. and lasted until 15.4±1.4 ka B.P., which was called the Gschnitz stadial, and Gschnitz was a toponym in Inn River region of Austria. At that time, precipitation was 2/3 of the present, temperature was 8.5–10.0 °C lower than today, and the ELA was 650–700 m lower than at present. Thus, the advancement of Gschnitz glacier was corresponding to the Older Dryas or the H1 event of the North Atlantic (Ivy-Ochset al., 2006; Bohlertet al., 2011).

After the Gschnitz stadial, another glacier advance,named Clavadel/Senders glacier advance, occurred. At that time the ELA was 400–500 m lower than today.Evidence is in the form of the moraines near Davos in eastern Switzerland and the moraines near Tyrol in Austria. The moraines at this time were 10 m high in average, but large boulders were not supplied to test the exposure time.

The boulders on 10 m high moraines near the Julier Pass in eastern Switzerland were dated to an exposure age of 13,210±610 a B.P., and the evidence was judged as another glacier advance somewhat later than Clavadel/Senders, and it was called the Daun stadial.During this period the ELA was 300–400 m lower than today.

The other three moraine ridges near the Julier Pass were also identified and named Egesen moraines. This type could be found in many valleys of the Alps, and its forming time was named as the Egesen stadial. Two of these moraines were dated in ages from 12.7±1.5 ka B.P. to 12.2±1.0 ka B.P. and 11.3±0.9 ka B.P., showing the presence of the Younger Dryas (Ivy-Ochset al.,2006; Bohlertet al., 2011).

An unstable climate continued until the Younger Dryas/Pre Boreal boundary, including the Pre Boreal oscillation. A moraine which is several kilometers away from the front of Kartell Ice Cirque in Austria was dated at 10.8±1.0 ka B.P.. The evidence indicated that another cirque glacier advance event occurred at the beginning of the Holocene, and this was called the Kartell stadial.

A small cirque glacier in Kromer valley on Mountain Silvretta in Austria advanced at 8.4±0.7 ka B.P., reflecting an 8.2 ka B.P. cold event in the early Holocene, called the Kromer stadial.

European scholars have reconstructed the glaciation scales of past several hundred years. For instance,they have reconstructed the evolution of the Rhone Glacier over the past several hundred years (Figure 4).The Rhone Glacier, one of the largest glaciers in the Alps, is the headstream of the Rhone River. Being one of three great rivers originating from the Alps, it crosses the central Alps at its western part, flows from east to west and into the Geneva Lake, and then flows into the Mediterranean. There are four small terminal moraines since the 14th century in front of the Rhone Glacier,which signal the advancement of the glacier during the Little Ice Age (LIA). The observation to the Rhone Glacier started in 1956 when it was a wide tail glacier and afterwards it kept retreating. Figure 5 shows the curve of the glacier change since the Last Glaciation based on numerous scholars’ research achievements.

ignificance

In this paper, we briefly introduce European research on the glacier advancement and retreat in the Alps regions since the Pleistocene. We find that the dating data of older glaciations in the Pleistocene are still limited, so more technical methods are required.As for the glacier advance sequences since the LGM,detailed studies have been accomplished by the use of the nuclide exposure dating method. Some well-known climate events proved by many other records since the late Pleistocene were all revealed through numerous types of glacier records in the Alps (Figure 5). Therefore, alpine glaciers are also ideal for reconstructing climate change since the Last Glaciation. Under the background of glaciers retreating altogether in the Post-Glacial, the glacial advances in the Alps occurred constantly; the glacial advance became shorter and shorter in distance so that each moraine was reserved in the valleys. This is the deep impression we obtained from glaciation researches of the Alps.

Figure 4 The terminal moraine (left) of the Rhone Glacier and the glaciated valley (right) at its front

Figure 5 Glacier advances since LGM and their 10Be data in the Alps (Reitner et al., 2011)

The Tibetan Plateau is over ten times larger than the Alps in area. The area of present alpine glaciers is about fifteen times of the Alps’, and the ELA (equilibrium line altitude) is 2,500 m higher than that of the Alps on average. Glaciers in the Tibetan Plateau belong to the high altitude glacier type in low-middle latitude monsoon region (part of westerly region), with a diversity of glaciers types. Unfortunately, detailed research on any glacier in the Tibetan Plateau cannot be comparable to detailed research on the Rhone Glacier in the Alps. For example, plentiful moraines are kept well in the valleys of southeastern Tibet where it is influenced by Indian monsoon. It is therefore possible to establish a detailed short-term climate change sequence, herewith to explain the environmental change features in the strongest seasonal monsoon prevailing region in the world. Besides, in the Tianshan Mountain and Altai Mountain regions there are also numerous glaciation problems to be solved. In a long time to come, we still need to cooperate with scientists and laboratory in the developed country due to large gap between China and Europe in technical means and laboratory construction. The prospects of research on glaciations and climate change in the Tibetan Plateau are broad and there is a way for who has will.

The study was supported by funds from NSFC(41171014, 40771049). The author would like to thank professors Naki Akcar, Jurgen Reitner, Markus Fiebig,Susan Ivy-Ochs and Max Maisch for organizing the excursions!

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