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In February 2010, a violent earthquake struck Chile, causing a tsunami 10 m in height. Affecting millions of people, the earthquake and giant wave also transformed the appearance of the coastline: the dunes and sandbars were flattened, and the coast subsided in places by up to 1 m. But although the inhabitants are still affected for the long term, the shore system quickly rebuilt itself. A team from IRD and its Chilean partners( 1) showed that in less than a year, the sedimentary structures had reformed. The Chilean coast therefore represented a unique “natural laboratory” for studying coastal formation processes. The subsidence of the coast also revealed the effects of rising sea levels on shores.
The mangroves of Guyana, in South America, are gradually disappearing. Contrary to the coastline of its near neighbour, French Guiana, which is still relatively protected, that of Guyana has been largely developed. In order to develop agriculture and aquaculture, earth dikes were built, destroying the greater part of the mangrove forest.
A study( 1) conducted by IRD researchers and the University of Aix-Marseille shows that the reduced protection provided by mangroves against the swell will lead to the large-scale erosion of 370 km of the country's coastline. Only one ecosystem restoration programme will help contain this phenomenon.
Over 99 % of the Earth’s fresh water exists in ice formations or underground. IRD geophysicists, aiming to find ways of detecting this resource, are at the spearhead in the development of an innovatory method based on nuclear magnetic resonance. To date, it is the only technique applicable for detecting liquid water underground or under a glacier from the surface and for estimating the volume.
This method recently found an original application as an aid for warning of glacier hazard. It successfully detected the presence of an immense water pocket of 55 000 m3 sitting under the Tête Rousse glacier in Haute-Savoie. This posed a flooding threat to people living in the valley below. Warning was given and the local authorities conducted a draining operation.
This technique is adaptable to glacier risk management, but it can also help for water supply provision. It can benefit both tropical mountain areas, such as the Andes or the Himalaya where glacial water can be a major threat, given the context of climate change, and semi-arid regions where water resources lie stored deep underground.
For many centuries, men have been exploiting the mineral wealth of the Andean Cordillera. The Incas, then the Spanish, extracted the gold and silver which gave their empires their splendour. Still today, gold and silver, but also tin, zinc, antimony, arsenic, cadmium and other metals are worked intensively. However, it is one of the most highly polluting of all human activities. Mines can eject enormous quantities of heavy metals into the environment. They are well known for their toxicity, yet poverty and strong economic dependence on raw materials mining too often lead to neglect of the environmental and health impacts.
Impressive cities have built up around these mines. This is the case of Oruro, perched 3 700 m high on the Bolivian Altiplano. The city has become one of the largest mining centres in Bolivia. Since 2006, in the context of the ToxBol programme, a multidisciplinary team involving the IRD and its partners( 1) has been investigating the origins, spread and effects of mining pollution on the environment and the health of the communities who live there.
On 27 February 2010, a huge earthquake, with magnitude 8.8, shook Chile. It left 500 dead and 13 million Chileans were affected, amounting to nearly 80 % of the country’s population. The event was one of the six most powerful earthquakes since the beginning of the 20th Century. Coast uplift has been proved by research scientists from Chile, France, and Germany( 1). This rise reached as high as 2.5 m and resulted in an advance of the shoreline of as much as 500 m towards the sea in places. Conversely, in the hinterland, the ground subsided by nearly 1 metre.
Since 1835, date of the previous strong earthquake in this zone, the equivalent to 12 m of deformation of the earth’s crust, resulting from tectonic block convergence, had been stored at the contact zone between the Nazca Plate and the South-American Plate. On 27 February 2010, rupture of the lithosphere( 3), along a 500 km long fault segment, released most of this mechanical energy in a single abrupt shock.
This study helps better understand the seismic cycle, with the long-term objective of finding ways of predicting and preventing the seismic risk.