Geological Intermezzo in Colombia

Heading west, we experienced the stunning topography of Colombia. The country is divided into three prominent mountain chains (Cordilleras) separated by extraordinarily flat valleys. Excellent infrastructure built in a highly challenging terrain (applied geology!) allows one to experience 4000 m of altitude change within a few hours of driving. In contrast to typical alpine-type mountain chains, Colombian mountains are covered with tropical forests reaching up to 3500 m, directly followed by unique meadows called the Páramo. This very special high-altitude vegetation is a crucial water reservoir for nearby farmland, but also the megacities of Bogota, Cali and Medellin. As global warming causes Colombian glaciers to shrink, the Páramos have become the most important source of water. As you may imagine, the greed for land (i.e. profit) puts the Páramos in danger – for planting potatoes and selling them on local markets.

The endemic wax palms (Ceroxylon quindiuense) growing in the Cocora valley (the tallest palm trees in the world, reaching heights of up to 60 m) tell us a fascinating story the Andes. Having its habitat located at an altitude of somewhere between 2000 and 3000 m, fossil remains of this very special palm tree tell us that its migration started 50 million years ago from Antarctica (which was warm at that time), and proceeded northwards, with the rising Andean mountains. Experiencing the Colombian landscapes gives you an idea of why Colombia is considered to be one of the most biologically diverse countries in the world. More than 56,000 species make up various complex ecosystems.

The prominent 5321 m high Nevado del Ruiz is possibly the most impressive indicator of Colombia’s active geology. In all its beauty, this volcano is a serious hazard potential, which the world came to understand in 1985 when the city of Armero was wiped out within hours by lahars, mass flows of water, and volcanic debris liberated from glaciers melted by the erupting volcano. This tragedy which caused over 20,000 casualties, could have been less hazardous if authorities had heeded the concerns of the scientists monitoring the volcano.

After looking at the modern volcanoes on land we continued west to look at ancient volcanic activity that formerly took place on the seafloor and is now exposed high in the mountains of western Colombia. We glimpsed the tremendous magmatic activity under sea, shedding massive volumes of basaltic lava that eventually forms the oceanic crust. This process is still active today, in the same intensity as millions of years ago and delivers us precious metals such as lead, zinc, copper, and gold.

From this ancient sea we went to the real one, taking a flight to Cartagena on the Caribbean seashore. We felt it clearly as soon as we left the aircraft: you breathe in hot, salty air, full of the smells of unknown plants. The topic for the following days was the human impact on biodiversity in the Rio Magdalena delta area, where a simple road construction cut off crucial sea water supply to mangroves, causing a drastic collapse to the local ecosystem in just a few years. This affected local fishing communities that suffer from fewer fish, and increased the concentration of heavy metals as the filter capacity of the mangroves decreased or ceased altogether. However, small restauration projects yield promising results and raise the awareness of the local population, which gives us hope that the delta will recover one day.

The excursion ended with a visit to the Tayrona National Park in the Sierra Nevada de Santa Marta, where mountain glaciers can be seen from tropical beaches. The pieces of rocks exposed here are remains of the collision between the Northern American continent with South America some 400 to 500 million years ago. This intermezzo left traces for us to study, illustrating that everything on our planet is moving, including the largest continents; it is just a matter of time.

Ilya Fomin did his BSc and MSc in igneous petrology in Lomonosov Moscow State University. Further he moved to ETH Zurich for his doctoral studies in numerical simulation of Earth's mantle melting. Now he works in geophysics at Macquarie University in Sydney.

Nico Küter just finished his doctoral studies at ETH's Earth Science Departement, investigating the high-temperature fractionation behaviour of carbon isotopes. He co-organized the first Doctoral excursion to Taiwan in 2017, which was a perfect balance to his purely laboratory-based research project.

Richard Ott is a doctoral student at ETH working on earthquakes and landscape evolution in Greece. The Taiwan doctoral excursion 2017 inspired him to co-organize the doctoral excursion to Colombia.