With this first regular post I would briefly introduce one of my favourite field (in the geological sense) of interests – the periglacial zone and one of its largest and most characteristic landscape features.
The term periglacial was introduced by the Polish geologist Walery von Lozinsk in 1910 and 1911 to describe the particular mechanical weathering he had observed in sandstones of the Gorgany Range in the southern Carpathian Mountains. Here the intense daily and seasonally variations of temperature slowly but unrestless weakens the rocks; ice forms in the fissures and shatters boulders, finally the angular rock-rubble accumulates on plains, slopes or the base of a cliff. The term was intended to describe this facies ( the term refers in geology to the characteristics of a sediment) of lose rubble, but became soon adapted to name a zone outside the area occupied by glaciers and ice sheets, where a cold and dry climate, frost and ice, often hidden in the underground, forms particular features in the landscape.
Fig.1. An alpine landscape – characterised by glaciers and the periglacial zone – in this cold and dry environment the debris is formed mainly by the mechanical weathering of the rocks and accumulation in moraines and talus deposits of cliffs.
Today almost 23% of the land areas are located in the periglacial zone, large areas in the Polar Regions, the coasts of Greenland, the Tundra of North America and Asia, parts of the Scandinavian Peninsula, the highlands of the Himalaya and other mountain ranges like the Cascade Range, the Caucasus Mountains, the Alps and the Pyrenees.
Fig.2. Distribution of permafrost on the Northern Hemisphere modified after BROWN et al. 1998. 23% of the land areas are affected by permafrost, in the polar region permafrost can also be found under water (click to enlarge).
First observations on periglacial processes were reported from explorers venturing in the Siberian Tundra – in 1685-86 a delegate of the St. Petersburg Academy of Sciences discovered frozen soil and ice underlying unfrozen soil during an excavation in Yakutsk. Despite this and similar observations by locals and explorers in other Russian regions and North America there was no further interest by authorities for investigations on these phenomena in such a remote parts of the world.
Only in 1838 the Baltic German Karl Ernst von Baer (1792-1876), embryologist and explorer with experience in cold regions like Lapland or the Russian island of Novaya Zemlya, persuaded the Academy of Sciences to finance an expedition to study the strange behaviour of the temperatures in the Siberian underground. Von Baer prepared a detailed manuscript summarizing the knowledge of underground ice in Siberia – “Materialien zur Kenntnis des unvergänglichen Boden-Eises in Sibirien” (1843, Materials about the knowledge of the unfading soil-ice in Siberia) – and instructed the Russian zoologist and explorer Alexander von Middendorff (1815- 1894) how to accomplish the difficult task:
“1. Motivation and purpose of this collection of materials.
It has already become known to the public that since longer time the academy plans for a scientific journey, one of the main purpose of it will be to determinate more precisely, than until now had been done, the increase in soil temperature in the nearly 400 feet deep, driven in the ground-ice, well in Yakutsk.
The same journey will also collect other notes about the ground-ice in Siberia.”
In 1848, to measure the temperatures in the underground and to realize how deep the ice could reach, Von Middendorf used an old, 116 meter deep well, excavated in the years 1828 to 1837 in a vain attempt to find ground water for Yakutsk.
This was the first measurements of temperatures in Permafrost and Von Middendorf recognized that the temperature of the underground depended from the annual mean temperature and that only the uppermost part experienced major temperature changes between winter and summer. Soon Permafrost – frozen soil or rocks with temperature constantly at or below 0°C - was recognized and described also from other regions of the Arctic Circle.
Surprisingly, despite the similar conditions to Arctic areas, Permafrost was discovered late in mountain regions and especially in the Alps. The surface overlying Permafrost tends to defrost during summer and is hidden by snow during winter – underground permafrost is therefore not easy to spot and observe. Still in 1970 the discovery of underground ice in the Austrian Alp at 2.677 m during construction works was a surprise.
To map the distribution of Permafrost geologist can however rely on particular landscape features formed by the creep of the ice-rocks mixture – rock glaciers. Rock glaciers are common elements in the periglacial zone of the alpine environment and their number exceeds by far the number of “regular” glaciers.
Fig.3. View of a tongue shaped rock glacier in the Ötztaler Alps. Rock glaciers are debris accumulations with larger amounts of ice within; the ice deforms slowly due the gravitative pull, causing a measurable creep movement and the typical shape of the rock glacier. Two main typologies exist, in ice-cored rock glaciers the ice forms a central core covered by debris, in ice-cemented rock glaciers the ice fills the gaps between the boulders and debris.
However, in contrast to glaciers noted and observed already in ancient times, these features were neglected by travellers and researchers. Only in 1883 rock glaciers were described for the very first time from the island of Greenland. The American Spencer mapped them in the San Juan Mountains in Colorado as a particular form of debris talus, Capps studied them in Alaska and introduced in 1910 the term “rock glacier” – he presumed that these features were old glaciers, buried by rock debris. Other research showed however that rock glaciers also occur in regions never occupied by glaciers or ice shields. Despite the problem of the origin it was soon realized that these mixtures of ice and debris slowly move and flow, forming a characteristic lobate to tongue shaped form – in 1910 Tyrell introduced the term “Chrystocrenes“, meaning “flow of ice”, but the name was not adopted by other researchers.
For the next 30 years little progress was achieved – the distribution, age, origin and significance of rock glaciers remained poorly understand. Only with increased interest with constructions and engineering problems in periglacial zones (the Cold War reached also these areas) again research tried to solve the mystery surrounding the rock glaciers. In the last decade an ulterior significance of rock glaciers became obvious.
Climatic change can have an important effect on the distribution of permafrost in the middle latitudes, even a slightly warming of the mean air temperature and therefore surface temperature, can heavily affect the permafrost in the underground. By observing rock glaciers reactions (velocity of creep deformation, discharge) to the increase in the annual mean temperature in the Alps and other regions researchers hope to better understand and visualize the reaction of the hidden underground ice. The strong retreat of glaciers is obvious, but permafrost was though to react much slower, because of the insulation effect of the covering debris layer. But observations of temperature profiles in drill holes showed that percolating water, resulting from the melt of more superficial ice, can “transport” heat much faster deep in the underground than previously theorized.
Fig.4. and 5. Front and “thermokarst” – as result from the melt and collapse of the ice core – of the rock glacier “Hohe Gaisl” in the South Tyrolean Dolomites.
BRESSAN, D. (2007): Aufbau und Dynamik aktiver Blockgletscher am Beispiel der Lazaunalm (Ötztaler Alpen / Südtirol). Univ. Dipl.-Arb., Fakultät für Geo- und Atmosphärenwissenschaften Innsbruck: 198
BROWN, J.; FERRIANS, O.J.; HEGINBOTTOM, J.A. & MELNIKOV, E.S. (2001): Circum-arctic map of permafrost and ground ice conditions. Boulder, CO: National Snow and Ice Data Center/World Data Center for Glaciology. Digital media. http://nsidc.org/, Versions 2001, 2002 & 2005
FRENCH, H. (2003): The development of Periglacial Geomorphology: 1 – up to 1965. Permafrost and Periglacial Processes 14: 29-60
SHRODER, J.F.; BISHOP, M.P.; COPLAND, L. & SLOAN, V.F. (2000): Debris-covered glaciers and rock glaciers in the Nanga Parbat Himalya, Pakistan. Geografiska Annaler 82(A): 17 – 31