Chile is an ideal study site for geologists, due to its exceptional climate gradient. Over the past few hundred years, climate but also human activities have severely impacted soils in this country.
Chile is one of the few countries in the world with a territory spanning more than 4,000 km, from an arid desert in the north to one of the wettest regions of the planet in the south. Such a temperature gradient makes it an ideal place for researchers to study the impact of climate on erosion. French and Chilean scientists have been working hand in hand on this issue for 25 years. An initial inventory of their internationally recognised joint research was published in the Geomorphology (1) journal.
The role of El Niño
“The topography of Chile, located on the steep slopes of the Andes mountain range, is a major erosion factor, states IRD geologist Sebastien Carretier. It makes the impact of climate difficult to determine in the long run. However, for the first time we managed to quantify the role played by extreme events in the country’s erosion. The effects of El Niño events are greater on the arid lands of northern Chile, where there is less rainfall. In this region, it accounts for 90% of average erosion over millennia. Conversely, in southern Chile where rainy spells are more frequent, El Niño has less impact on erosion, around 10%. Therefore there is a gradient of the erosive effect of extreme events depending on the climate”. The arid climate affects the condition of soils: very sensitive to change, they break easily, especially during wet periods when they experience massive rainfall.
Aggressive human activity
Nevertheless, climate is not the only land degradation factor: human activities, which are concentrated in the central part of the country (from Santiago to the Araucania region) are also a key contributor. “Deforestation and soil erosion are as old as human presence in these regions, as they started approximately 12,000 years ago, explains Chilean geomorphologist Violeta Tolorza. However, Incan agriculture was not aggressive; landscapes consisted of forests, interspersed with areas intended for farming and herding. When they arrived, Spanish settlers destroyed primary forests to build cities and boats as well as plant wheat. More than 15 million hectares of forest in total were burnt up until the early 20th century”.
After becoming the breadbasket of the world under the impetus of the Spanish, Chile’s production capacity plummeted throughout the centuries. So much so that the country had to import this cereal from 1936. In the Araucania region, trees no longer grow. Primary forest loss and the leaching of fertile land since the 16th century have destroyed soil. “The deforestation policy continued under the dictatorship of Augusto Pinochet (1973-1990), while pine and eucalyptus plantations were encouraged, adds Sebastien Carretier. Even today, there is no actual political awareness of the problem”.
Plant cover and geological movements
Researchers have determined the protective role of plant cover against land degradation over a period of two to three centuries. On a longer time scale of thousands or even millions of years, the effects of plants on geological ground movements remain unclear. Even though they retain soils, forests contribute to their development and increase land masses which may disappear as a result of floods or earthquakes. Improving the understanding of the links between erosion, Earth dynamics and the plant cover is one of the future focal areas of Franco-Chilean researchers.
1. S. Carretier, V. Tolorza, V. Regard, G. Aguilar, M.A. Bermúdez, J. Martinod, J-L. Guyot, G. Hérail, R. Riquelme, Review of erosion dynamics along the major N-S climatic gradient in Chile and perspectives, 2017.