- Created: Thursday, 07 April 2011 10:45
- Published: Thursday, 07 April 2011 10:45
- Written by Administrator
- Hits: 34121
ALPINE GLACIAL KARST: THE SHAPE OF WATER-HOLES
Exploration project of “water-holes”, cavities created by melting within large glaciers. Our association has worked on glaciers all over the world for over 20 years studying caves that develop at the centre of glaciers. We started from the Alps, on the Gorner Glacier, where modern glacial speleology has its origins, and we carried out investigations on glaciers in Central Asia, Iceland, and Svalbard, but focusing our efforts mainly on Patagonian glaciers. More recently we carried out the first speleological expedition in the Sixth Continent and investigations in northern Svalbard.
Over the years we identified phenomena creating caves and the internal drainage structure of temperate glaciers, namely those with temperatures around 0 °C. We call this type of glacial speleology “traditional” because it is the most common type in ablation areas of glacial tongues.
Caves generate from surface melt water, which, gathered in streams, penetrates into the centre of glaciers through the energy of waterfalls.
In general, caves are not very deep, they normally reach no more than one hundred metres, because below this level the pressure on the ice obstructs any cavity and is totally impermeable to any flow, even if there can be cavities full of still water.
Let us consider that, in the temperate ice, crevasses are up to 20-25 m deep, because ice at the bottom of the crevasse flows and fills tectonic caves. In the case of caves, ice collapsing on the cavity is removed from the water flow.
We are currently trying to understand the phenomenon of glacial karst in some “non-traditional” cases. Geographical area: large temperate glaciers, with ice temperature around 0 °C, from Iceland to Tien Shan, from the Alps to the Karakorum.
Future plans: the theory of glacial karst is clear, except in submerged areas where it is necessary to carry out direct explorations. At present we are following the development of this phenomenon with the retreat of glaciers.
The second largest glacier in the Alps. The Gorner Glacier is the second largest glacier system in the Alps (around 65 km2) and generates from the confluence of various tongues coming from the ridge connecting the Monte Rosa to the Breithorn, at an altitude between 2200 and 4600 m.
The most important feature of this glacier is its unique surface morphology which makes it one of the world’s most interesting glaciers. The surface of its final part (the so-called “ablation region”), at an altitude of 2200 to 2700 m AMSL, is characterised by glacial rills (known by the French term «bedières»), small valleys and deep shafts («glacial moulins ») absorbing surface water and transporting it in the glacier’s depths.
Various explorations carried out over the years have allowed the discovery of around 30 caves with different morphologies, with long sub-glacial meanders and shafts more than 100 m deep. Many of these glacial moulins, explored several times since 1985, seem to have a stable position and a structure that replicates over the years with only slight variations.
The Gorner Glacier is shrinking rapidly as a result of climate change in these warm years. Paths that up to some years ago led to the ice surface now end up at small walls that see the light after various centuries. Nothing to worry about, unlike mountains, glaciers are among geological structures that give us the clearest idea of change. Some millennia ago the glacier which has now retreated under the Monte Rosa filled the entire valley up to Visp, hiding various mountains. Around 1,000 years ago it had retreated, emptying the valley where we can observe its transformation today. At that time, up until the whole middle age, the two main glacial tongues were separated and ended in a vast lake at 2200 m AMSL. Then, with the cooling of the climate, the glacier moved forward up until the mid XIX century, when glacier advance attracted the interest of people causing the creation of a discipline studying this phenomenon, glaciology.
The lake that filled the valley aroused the curiosity of speleologists. Glacial caves are to be found especially where surface melt water can join together in large streams up to where it finds the point where the ice surface is weaker. From there melt water plunges down expanding the hole that it falls into, which turns into a rumbling precipice. The smaller the surface inclination, the bigger the stream becomes, though this is normally a feature of immense glaciers at the limit of the Polar Regions and not of alpine glaciers, which are beautiful, important, well-studied, near but certainly not big.
The Gorner is a key alpine glacier, thus it is very small. With its size it should be steeper to flow downhill, this way surface runoffs would scatter here and there and would be suddenly absorbed. This is not the case as the opposite slope makes the large ice mass slide less steeply so as to extend in horizontal planes, where streams become bigger and dig large precipices.
In the early 80’s the founder of glacial speleology in Italy, Mario Vianelli, performed an investigation on various alpine glaciers which allowed him to understand the exceptional nature of the Gorner with its streams, meanders, lakes and shafts. Since then, the glacier has become a famous destination for many explorers. At the beginning nobody really knew how to descend into those difficult cavities and the Gorner represented a perfect training ground. After working several times in remote lands, the glacier took on its real qualities: small but well-articulated, comfortable, the ideal place not only to attract new people to speleology but also to best understand the nature of karst glaciers. The Gorner for us is a bit like home. In the middle of the ablation area, beneath Gornergrat, a lake used to appear year by year, but in the last decade this has no longer happened. Normally, it used to disappear through a well that we have observed since 1986, the G6. Sometimes it slightly changes its shape, but it is always there while the glacier flows and takes on its form by passing from there. Around one hundred metres below the surface level it becomes a vertical tube that plunges into a puddle.
On one occasion, the author of this text was taking some notes at the bottom of the pit and a team mate, who was climbing up, detached a big sheet of ice thirty metres above. The sheet was falling and making a noise that could be heard by all team mates who were on the surface. Just one curve before reaching and killing me, my good old friend Gorner, made it explode and I was hit by a hailstorm that literally buried me, fortunately without hurting me too much.
Then there is Agassiz, the cavity absorbing the brook which develops at the foot of the glacier, towards the Lyskamm. It is extraordinarily deep, for a long time the deepest cave in the world with its 150 m (only giant glaciers in Patagonia or in the Arctic region could reach such depths). After Agassiz we have G8, its rival, amazing and more interesting, situated at the foot of the glacier descending from the Breithorn. Next there are central sub-horizontal absorption tunnels, small deep conduits flowing just beneath the surface.
The most difficult region to understand is, without any doubt, the one further downhill, under Rotenboden.
This karst area is difficult to access and is mostly made of lakes. At first we thought the area marked the end of glacial karst and therefore we didn’t consider it important. Although now we do still think it is the end of glacial karst, we think it is extremely important: here originates vast water basins closed in fragile ice dams and extending beyond Zermatt. Here is another case in which a small but complex glacier shows us that the immense water releases taking place on Patagonian glaciers and vanishing unperceivably in immense areas, is part of a phenomenon that, on a smaller scale, it can also produce; but on human buildings, not on the deserts of Lake Viedma. Now we have learnt to reach the Gorner in winter skiing down the Teodulo: we set off from home at 7.30, uphill from Cervinia towards Testa Grigia at 8.30 and we arrive on the Gorner at 9.00 with a little luck… From 2005 we have also learnt a new winter route, rather uncomfortable, down from Stockorn, on the hydrographical left of the stream, allowing us to reach the top of the glacier which is still sleeping under the snow.
Everything changes though.
The Gorner is clearly showing us that glaciers change, that climate changes, and that extraordinary things are happening in these years. It is seven years now that the glacier has almost stopped flowing downstream. Caves are no longer the main access of the ice to the sea; they remain the same year after year. Everything is still; the places we explored last year are the same today, walls too. Ice grows, charging tension in order to adapt to its own voids as it melts. Now in depth, the ice surface brutally explodes when it is just knocked by a nail or hit by a crampon.
In autumn 2004 the surface of a large area near the glacier front collapsed. Clearly, below the ice, at contact with the nearby rocks, a large zone had been created, around 60 m long, 30 m wide and 20 m high.
In this area a doline of this size opened up, and among the ice debris were to be found sub-glacial tunnels. The uphill side of this doline will become the new glacier front when the downhill ice mass, now isolated, melts completely.
This will be in just a few years now.
Iceland - Kviarjokull 1997
Explorations on the largest glacier in Europe. Iceland lacks limestone rock, but presents two other types of rock that can form caves, at the opposite temperature poles: volcanic lava and ice. The Iceland 97 expedition, organised by La Venta, the ETSIM of Madrid and the Explorers Club, aimed at studying caves that formed within the glacier Kviarjokull, a glacial tongue flowing down from Vatnajokull, a huge ice-cap located in the south-east part of the island.
Melt water flows on the surface creating large streams that penetrate into the ice where the surface is weaker and forms waterfall shafts and canyons entirely underground. The study of these structures is very recent and is opening a new frontier in glaciology because it makes clear much strange behaviour of glaciers. The study performed on the Kviarjokull allowed us to compare the shape and the size of this cavity with the tension structure of the glacial tongue. The second goal of the expedition was to perform an investigation of the main tongue flowing down from the Vatnajokull, the enormous Skeidararjokull. From here in 1996 flowed an immense river created by melt water caused by the eruption some days before in the southern part of the Vatnajokull. For some hours that stream, with a flow rate of over 50000 cubic metres per second, was the second largest river in the world. It flowed entirely underground inside the world’s largest cave. The investigation allowed us to study the final part of the river course, where a fiord, 300m wide and one km deep, has been dug in the glacier front. Corresponding with the point where the river flowed there was a depression in the ice surface, a sort of wide valley, but not deep. There were no traces of the cave which had probably collapsed in the weeks following the flow of water. We are currently trying to clarify the effect of climate change on glacial karst. There is a general phase of reduction of the mass of glaciers, that on one hand creates new internal structures, because the drainage reticulation evolves fron year to year; on the other the formation of new hypoglacial structures influences the regression rate of the entire glacier.