350 - Patagonian glaciers in danger
May 2010
Remote lands at the far Southern reaches of the Latin American continent, Patagonia and Tierra del Fuego, the archipelago at the extreme Southern end*, support the world’s most majestic monuments of ice. The Patagonian glaciers, including the famous Pio XI, the largest in Latin America with its 1292 km² surface area, standing high above the valleys of Chile to the West and Argentina to the East. The Tierra del Fuego icefields, plunge sheer into the ocean, deep into the meandering fjords.
These glaciers are retreating. The extent of their regression has recently been quantified at regional scale. An extensive survey by IRD researchers and their partners( 1), focusing on 72 of them, shows that the vast majority of the glaciers of Patagonia and Tierra del Fuego have diminished considerably since 1945. Some scientists consider them to have lost up to 40% of their former size.
A loud rumble resounds from the depths of the ice layer, which in places reaches further down than 1000 m. The glaciers, like immense frozen cathedrals with blue stained glass, crack, grumble then fall apart before hurtling with a great crash into the fjords or mountain lakes. In Patagonia and Tierra del Fuego, inhospitable lands at the southern tip of Latin America*, the ice giants are shrinking back year by year.
To assess the extent of this retreat, IRD glaciologists and their partners( 1) studied fluctuations in the length of the region’s 72 glaciers between 1944-45 and 2005. Their findings: the great majority had regressed substantially, some by nearly 40%.
A general trend of retreat
The position of the Patagonian glacier front was first described at regional scale in 1956, by the Franco-Chilean glaciologist Louis Lliboutry. He drew up sketch maps from aerial photographs taken in 1944-45. To estimate the extent of the retreat of these icefields, the researchers compared this type of historical map with remote sensing images taken by ASTER( 2) and Landsat satellites of NASA( 3) between 1973 and 2005.
Nearly 90% of the glaciers studied are affected. South of the 72 surveyed, only eight have remained stable while one has advanced. Marinelli Glacier, in the Darwin Cordillera, in Tierra del Fuego, holds the record, with a retreat of 12.2 km, amounting to a retreat of 37.6%, closely followed by the O’Higgins Glacier, in South of Patagonia, and San Rafael Glacier, in the North of the region, which show respective shrinkage of 11.6 km and 5.7 km.
Of the 30 which have retreated furthest, the small glaciers, with surface area less than 50 km², prove to be the most strongly affected. Most of them are located in Tierra del Fuego. The Patagonian ones are generally larger, with more gentle slopes. However, the survey revealed no direct relationship between the size of the glaciers and fluctuations in their length.
Every glacier reacts in its own way
This generalized retreat is probably the result of atmospheric warming, a process observed in the region. The very nature of glaciers makes them particularly sensitive to climate variability and change. Each has characteristic basin geometry, topography, ablation conditions at the front, response dynamics and response time( 4). These parameters also influence the melt rate. Most of the glaciers studied flow as tongues towards the sea or into mountain lakes, from which icebergs( 5) break off, leading to highly variable retreat rates. This type of glacier is characterized by abrupt phases of retreat followed by periods of stability. The San Rafael and O’Higgins Glaciers, for example, have been undergoing strong acceleration of their retreat since the 1970s. Conversely, the non-calving glaciers usually show a more linear type of retreat.
Data difficult to obtain
Aiming to find a more accurate explanation of the retreat process, the researchers now have to calculate the glacier mass balances( 6) and determine the glaciers’ response time, but also investigate the regional climate in more detail. At present, they have insufficient climatic series and ground data sets available because these hostile expanses of terrain, swept by frequent precipitations and violent winds, do not easily give up their secrets. The scientific instrumentation is difficult to maintain in the field and the omnipresence of cloud renders the satellite coverage poor.
The glaciers of Patagonia and Tierra del Fuego have regressed considerably since 1945. If the current climatic conditions persist, the icefield retreat will continue. In the medium term this prospect jeopardizes the Chilean government’s mega hydroelectric power schemes, which would entail the construction of a series of dams. Another vital issue, of global significance: icefield melt contributes significantly to the global sea-level rise, with the risk of generating large numbers of climate refugees in the world.
1. This research work was conducted jointly with scientists from the Centro de Estudios Científicos at Valdivia, Chile, of the Laboratoire de Glaciologie et Géophysique de l'Environnement (UMR University of Grenoble 1, CNRS), from the Centro de Estudios Avanzados en Zonas Áridas at La Serena in Chile and the University of Utrecht in the Netherlands.
2. Advanced Spaceborne Thermal Emission and Reflection Radiometer
3. National Aeronautics and Space Administration
4. The time necessary for a glacier to adapt to changes in its mass balance.
5. Glaciers are said to “calve”.
6. The mass balance is an evaluation of the difference between snow accumulation and ablation or loss of ice.
* Did you know?
The Southern point of the Latin American continent is separated from the continent by the Magellan Strait. It owes its name “Tierra del Fuego” to Magellan who, the first time he voyaged round this territory in 1520, saw columns of smoke. The smoke was in reality coming from the local Indian communities, peoples who have since disappeared, who kept a fire going permanently in their boat or in their shelter to stay warm.
Rédaction DIC – Gaëlle Courcoux
Translation - Nicholas Flay
