Patagonia's 'Warm' Glaciers .....
“The glaciers of Patagonia are some of the most temperate, fastest and most erosive glaciers on the earth,” says the glaciologist Michele Koppes from the University of British Colombia. While moving forward, they plane off the landscape more intensively than giant glaciers anywhere else in the world. This, of course, has something to do with climate change. Increasing temperatures accelerate the speed of glacial ice, which flows from the vast ice fields in the Andes, Campo de Hielo Norte and Campo de Hielo Sur, down to sea level – with far-reaching consequences.
The San Rafael Glacier is Patagonia’s fastest-moving glacier. It moves forward at a rate of up to 7.6 kilometres per year on its way down to Laguna San Rafael from the Northern Patagonian Ice Field Campo de Hielo Norte. This corresponds to approximately 21 metres per day. The San Rafael Glacier is 45 kilometres long and about 2.5 kilometres wide. At its front edge, the ice wall is up to 70 metres high.
Why does ice move so fast and why is it ‘warm’….? Researches differentiate between temperate or 'warm' and cold glaciers. 'Warm' glaciers are located in the warmer latitudes of our planet, in the moderate climatic zone, with an average annual temperature of 10 degrees Celsius (with a fluctuation range of 30 degrees below zero and 30 degrees above zero). Especially in the summer, glaciers are honeycombed with cavities in which melt water from the glacier surface gathers in so called glacier mills, drains off on the surface and swirls through the inner ice mass carving out entire tunnel systems in the process. Additionally, more melt water comes into existence due to the pressure of the ice within the glacier itself (pressure melting). When this melt water trickles down to the rock at the bottom of the glacier, it can have an effect similar to that of a lubricant, which means that especially in the summer, 'warm' glaciers can creep toward the valley much faster than cold glaciers situated at the Poles, in Greenland and the Antarctic where the temperatures are mostly far below zero - they are often frozen solid at the base.
….. and why is it so blue? Always, when glacial ice is very dense, that is when it contains very few air bubbles, it absorbs a great part of the sunlight and only the blue light out of the whole spectrum is reflected. This makes it look blue. When, on the other hand, glacial ice contains many air bubbles, it disperses light and as a result takes on white or grey hue.
The faster the glacial ice flows, the stronger is its erosion force, which means that it scours away more layers of the bedrock and drags the debris along to form deep dells underneath it. Along with it comes the rubble, which falls down on the ice from the surrounding mountains.
The 35-kilometre and circa 2-kilometre wide ice tongue of the Viedma Glacier flows out of the second largest ice field in Patagonia - Campo Hielo Sur - into the water of Lake Viedma at its front. It is located on the Argentinian territory. The debris which has broken off from the rock faces flanking the glacier and tumbled onto its ice tongue, is transported down the mountains in many morain bands.
The consequences of climate-induced glacial retreat are distinctly manifasted by the Colonia Glacier, which , like the San Rafael Glacier, flows down the Campo Hielo Norte.
Its ice tongue has dramatically retreated within the last few years. Today there is a melt water lake in the former glacier bed. The sediments that the glacier has carried down from the mountains and deposited while retreating, form a sort of a land bridge with a canal. It slows down the outflow of melt water with icebergs floating in it.
Lago Cachet II – a melt water lake situated a few kilometres further up in the mountains at the right edge of the glacier - poses a serious risk. Several times a year the pressure of melt water on the glacier’s tongue becomes so strong that it breaks through its edge. However, masses of melt water do not flow on the ice surface but plunge through a tunnel system naturally carved in and underneath the ice of the Colonia Glacier. On their way toward the valley, water masses swell in mighty swirls, reappear at the front of the glacier and flow into a large melt water lake. From there, water rushes through the canal in the land bridge endangering some villages in the valley and their rural surroundings on its way. (Not to be seen in the picture). Twice or three times a year the water level there, within hours, can rise up to six meters in height, which is a result of the water pouring out of the lake high up in the mountains.
A few years ago, the scientists at the Dresden Technical University installed an early warning system by Lago Cachet II near the edge of the glacier. It helps to monitor the water level in the lake and predict an impending outpour. Chilean glaciologists from Punta Arenas (Magellan University) are currently researching the condition of the ice at the edge of the Colonia Glacier in order to find out why suddenly the ice succumbs to the pressure of melt water and to trace the way the outpouring lake water takes when it flows into the Colonia Glacier’s tongue.
The American space agency NASA has assessed satellite pictures of Patagonia’s ice fields taken within the last 20 years and published a record of glacial movements there in the form of a map.
Both vast ice fields of the glaciers in the Patagonian Andes together cover the surface of 17,000 square kilometres – the Northern Patagonian Ice Field covers the surface of good 4,000 square kilometres and the Southern Patagonian Ice Field about 13,000 square kilometres. Campo de Hielo Sur is the largest ice mass in the southern Hemisphere after the ice shield in the Antarctic.
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