Autor: David Bressan

„It has already been said, that no small part of the present work refers to the nature and phenomena of glaciers. It may be well, therefore, before proceeding to details, to explain a little the state of our present knowledge respecting these great ice-masses, which are objects of a kind to interest even those who know them only from description, whilst those who have actually witnessed their wonderfully striking and grand characteristics can hardly need an inducement to enter into some inquiry respecting their nature and origin.“

James, D. Forbes (1900): Travels Through the Alps.

Today glaciers are studied worldwide and monitored as climate proxies, and the recent measurements show that almost all of them are retreating. The story about glaciers, their influence on the landscape and their possible use to reconstruct and monitor climate is an intriguing one, with many triumphs, setbacks and changes of mind.

For centuries, if not even millennia, the high-altitude regions of mountain ranges were visited and traveled by man, however, they were also forbidding places. The glaciers, masses of ice enclosing peaks and extending their tongues into valleys, were considered haunted by mountain spirits.

Despite such myths, there were some early insights of what glaciers actually really are. Greek historian and geographer Strabo (63 BC – 23 AD) describes a voyage through the Alps:

„… there is no protection against the large quantities of snow falling, and that form the most superficial layers of a glacier … []. It’s a common knowledge that a glacier is composed by many different layers lying horizontally, as the snow when falling and accumulating becomes hard and crystallizes … []“

However, this early knowledge got lost and was only rediscovered in the Renaissance. Between 1538 and 1548 glaciers were labeled (even if not depicted) with the term „Gletscher“ on topographic maps of Switzerland. The first historic depiction of a glacier is considered the watercolor-painting of the Vernagtferner in the Ötztaler Alps, dated to 1601. The Vernagtferner was a glacier that repeatedly dammed up the glacial lake Rofen, which outbursts caused heavy damage and loss of property, particularly in the years 1600, 1678, 1680, 1773, 1845, 1847 and 1848.

Swiss naturalist Johann Jakob Scheuchzer, visiting in the year 1705 the Rhône Glacier, published his observations of the „true nature of the springs of the river Rhône“ in the opus „Itinera per Helvetiae alpinas regiones facta annis 1702-1711″, and confirms the idea that glaciers are formed by the accumulation of snow and they move and flow. The increasing interest to study glaciers in the Alps is also encouraged by enthusiastic travel reports. A.C. Bordier describes in his „Voyage pittoresque aux glaciers“ (1773) the Bosson glacier as a „huge marble ruins of a devastated city.“ Swiss naturalist Horace Benedict de Saussure was fascinated by the mountains of his homeland and an enthusiastic alpinist. After 1760 he traveled more than fourteen times through the Alps (considering the possibilities in this time an extraordinary achievement) to explore valleys and mountains. In the years 1767 to 1779 the first volume of his „Voyages dans les Alpes“ was published, where he collected his observations and theories about the visited glaciers. He recognized moraines and large boulders as the debris accumulated by the glacier and proposed to map them to determine the former extent of glaciers. Despite this exact statement, de Saussure failed to connect large boulders found in the foreland of the mountains to the glaciers of the Alps. He assumed that these rocks were transported to their recent locations by an immense flood. The biblical flood explained why boulders found scattered around the plains of Germany came from outcrops located in Scandinavia or the Alps. However, to transport the boulders from the mountains, the flood had to reach 1000s of meters.

Despite such problems, the idea of a flood as the explanation for „glacial“ deposits in Europe was largely accepted. Even famous 19th-century geologists like Charles Lyell and Charles Darwin assumed that huge erratic boulders were transported by ice-rafts. That glaciers could flow far out of their valleys was, however, not an impossible idea for local inhabitants, who observed and experienced the growth and retreat of glaciers.

In 1815 the Swiss chamois hunter Jean Pierre Perraudin discussed with the engineer Ignatz Venetz his theory of former glaciers covering the Val de Bagnes. Impressed by such an idea, Venetz mapped geological features that made him recognize that not only the studied valley was once covered by ice, but the entire Swiss Alps. Vernetz’s lecture at the assembly of the Swiss Association for Natural History in 1829 was meet little interest. Only Jean de Charpentier, director of the salt mine in the city of Bex, was interested in this new theory. Charpentier himself started a detailed mapping project and in 1834 presented before the Swiss Association the results of his investigations, but again the ice-age theory was met with more criticism than interest. One of the critics in the public was a former student of Charpentier, named Jean Louis Rodolphe Agassiz, a young but respected paleontologist. Charpentier invited Agassiz to visit the city of Bex and surrounding mountains, to observe the recent glaciers and test the theory of former glaciers covering the Alps. In 1837 Agassiz held an enthusiastic lecture about glaciers and ice-ages. Three years later he published a detailed study of modern glaciers in his „Etudes sur les glaciers.“ However, even Agassiz experienced the same skepticism as many other ice-age proponents before. His friend, the

„I think that you should concentrate your moral and also your pecuniary strength upon this beautiful work on fossil fishes … In accepting considerable sums from England, you have, so to speak, contracted obligations to be met only by completing a work which will be at once a monument to your own glory and a landmark in the history of science … [] … No more ice, not much of echinoderms, plenty of fish …“

German geographer Alexander von Humboldt in a letter to Agassiz.

However, Agassiz didn’t surrender to criticism so easily and decided to use his good connections to the most important geologists of his time to popularize the ice-age theory. Agassiz’s research on the Unteraar-glacier in Switzerland established the foundations of glaciology; he recorded the dimension of the glacier, its velocity and even ventured inside the glacier by passing through a glacial mill. Soon after, the measurements methods introduced by Agassiz were carried out on various glaciers of the Alps and repeated nearly every year. The historical records showed various fluctuations, but since 1850 the glaciers in the Alps are quickly retreating. Especially in the last decades, the vanishing glaciers are a cause of concern, as they are unequivocal signs of a warming climate.

Literatur:

• KRÜGER, T. (2008): Die Entdeckung der Eiszeiten – Internationale Rezeption und Konsequenzen für das Verständnis der Klimageschichte. Wirtschafts-, Sozial- und Umweltgeschichte Bd., Schwabe Verlag: 619

„Like Venus, the theory of plate tectonics is very beautiful and born out of the sea.“

R. Trümpy, 2001

For over 200 years the Alps have been visited by geologists. For most of this time, they wondered how mountain ranges like the Alps formed. Folded sediments suggested forces pushing and squeezing the rocks. In the 18th century Swiss naturalist Johann Jakob Scheuchzer depicts and describes folds in the Swiss Alps, explaining them as layers deposited and then folded by the biblical flood.

German geologist Leopold von Buch (1774-1853) was convinced that mountains form like a bubble in Earth’s crust. Large magma intrusions displace and fold the superficial sedimentary layers. Von Buch believed that his theory could also explain the complex geology of the Alps, with magmatic and metamorphic rocks forming the inner zones and sedimentary rocks (like found in the Dolomites and the Northern Calcareous Alps) forming the outer borders. Based on von Buch’s research, French geologist Elie de Beaumont proposed that tilted and folded layers of different age were formed by periodic „magmatic“ pulses. At first, the horizontally deposited sediments are uplifted by the intrusion of a magmatic core. In a second phase, the layers become tilted and then new layers form by the erosion of older layers. The undeformed layers are tilted by a new orogenic cycle and so on. However, British geologists later showed that this theory couldn’t work as proposed. If a mountain formed around a magma intrusion, all the sedimentary layers should show similar strike and dip, but the strata in the Alps were tilted chaotically.

A new theory – the Contracting Earth theory – was later formulated by American geologist James Dwigth Dana. This theory explained mountains and continents as products of a cooling and shrinking Earth. Like the surface of an old and dry apple, the shrinking Earth would develop fissures (basins) and wrinkles (mountains).

Austrian geologist Eduard Suess suggested in his book Die Entstehung der Alpen (1875; The Origin of the Alps) and multi-volume work Das Antlitz der Erde (1883-1909; The Face of the Earth, English edition 1904-1924) that deep-sea trenches found along the borders of the Pacific Ocean are zones where the seafloor is pushed beneath the continents. However, also Suess imagined that „the horizontal and uniform movements“ of rock layers could be explained by variations in Earth’s circumference. In 1906, Austrian geologist Otto Ampferer imagined with his “Unterströmungstheorie“ large currents in Earth’s mantle, pulling the upper crust, creating mountains like folds in a carpet. However, Ampferer and many other geologists working in the Alps used such theories only to explain very localized tectonic movements, like the thrust belt found in the Northern Calcareous Alps, mapped by Ampferer.

Thrusts had been noted in the Alps since the middle of the century, for example by Bernhard Studer (1853) and Arnold Escher (1841). In the Glarus Alps a spectacular thrust – here older Permian red beds and Mesozoic limestone cover younger Eocene to Oligocene Flysch – was explained by Escher and later by Albert Heim as a large „double fold“, a recumbent fold with inverted layers. In 1884, Marcel Bertrand proposed that a single, north-facing tectonic nappe could explain the inverted stratigraphy. The nappe was thrusted on older layers by the gravitational collapse of the mountains, when single sheets of sedimentary rocks sliding downwards get stacked atop each other.

The Contracting Earth theory could explain the immense forces needed to crack and fold rocks on a global scale. However, it failed to explain the irregular distribution of mountains on Earth. According to the Contracting Earth theory,  features like mountain ranges should be distributed randomly on the uniformly shrinking planet. However, even a short glimpse on a map or globe shows that mountain ranges are not randomly distributed, but rather form long chains, like the Alps, the Caucasus and the Himalayas; or are instead found along one side of a continent, like the Rocky Mountains or the Andes, but not on the other side.

In January 1912 the German meteorologist Alfred Wegener presented in his public lecture Die Heraushebung der Großformen der Erdrinde (Kontinente und Ozeane) auf geophysikalischer Grundlage (The formation of large features of Earth’s crust (Continents and Oceans) explained on a geophysical basis) for the first time his idea of the ancient supercontinent Pangaea, from which all modern continents split apart. Three years later he publishes his book Entstehung der Kontinente und Ozeane, translated in the third edition and published in 1922 as The origin of continents and oceans. According to Wegener, ocean basins form as continents split apart, mountains are formed as continental crust collides with the oceanic crust or other fragments of continental crust. Swiss geologist Émile Argand used in 1916 Wegener’s hypothesis to explain the closure of the Tethys Ocean, once located between Europe and Africa, and subsequent folding and overthrust of marine sediments on the continental crust of Europe.

Despite Argand’s nappe theory could explain many mysteries of Alpine geology, like old and young rocks found together or the tectonic structure of the Alps, it would need almost another 50 years until it was widely accepted.

Wegener’s continental drift theory (a catchy phrase adopted mainly by his critics, as Wegener talks more general of displacement theory) was received with mixed feelings. Most geologists regarded it as cherry-picking of data. Only a few geologists became convinced of his idea. Wegner himself reacted to the critics and tried to respond to them in various editions of his book, however with moderate success. The greatest problem facing Wegener was the lack of direct evidence for the movements of continents. No mechanism was known to be powerful enough to move entire continents. Wegener proposed gravitational pull, tidal and centrifugal forces, but British geophysicist and astronomer Harold Jeffreys (1891-1989) demonstrated that such forces are too weak to explain moving continents. Wegener will die in 1930. His continental drift theory is in many aspects erroneous. Not the single continents move, but fragments of Earth’s crust and the driving forces comes from within the planet, not from the outside. But Wegener’s work introduced the idea of moving continents to the scientific community and the public and decades later this legacy will influence a new kind of theory – modern Plate Tectonics.

Between 1959 and 1977, geologists Marie Tharp and Bruce Charles Heezen, published the first maps of the seafloor, showing what seemed to be large rift zones, where new crust can form as lava pours out from submarine fissures. Canadian geologist John “Jock” T. Wilson introduces in the 1960s with the mid-ocean ridges (where new crust forms), subduction zones (where old crust sinks back into Earth’s mantle) and transform faults (accommodating lateral movements) the modern elements of plate tectonics. Harry Hammond Hess, US Navy commander at Iwo Jima, a prospector in Zambia and later professor at Princeton, in 1962 publishes a paper that will become one of the most widely cited geophysics paper for years. He hypothesized that the seafloor widens along the mid-ocean rifts and crust movements are driven by currents in Earth’s mantle, providing also a mechanism for plate tectonics and so mountain building. (to be continued).

References:

• DalPIAZ, G.V. (2001): History of tectonic interpretations of the Alps. Journal of Geodynamics 32: 99-114
• FRANKS, S. & TRÜMPY, R. (2005): The Sixth International Geological Congress: Zürich, 1894. Episodes, Vol. 28, no. 3: 187-192
• HEIM, A. (1919-1922): Die Geologie der Schweiz.
• SEARLE, M. (2013): Colliding Continents: A geological exploration of the Himalaya. Oxford University Press: 438
• STÜWE, K. & HOMBERGER, R. (2011): Die Geologie der Alpen aus der Luft. Weishaupt Verlag: 296
• TRÜMPY, R. (2001): Why Plate Tectonics was not invented in the Alps. Int J Earth Sciences Vol. 90: 477-483
• TRÜMPY, R. & WESTERMANN, A. (2008): Albert Heim (1849-1937): Weitblick und Verblendung in der alpentektonischen Forschung. Vierteljahrsschrift der Naturforschenden Gesellschaft in Zürich 153(3/4): 67–79