The El Toqui zinc mine (30/01/09)

In Coyhaique, Fabien helped us to get in touch with an officer of the El Toqui mine, located 90 km further north. We got an appointment with a geologist from the Coyhaique office before going on with our bikes. Two days later, we were at Villa Mañihuales, a small village close to the mine. We had originally planned to get to the mine by bike, but we learnt that a daily bus carries the minors and that we could also take it. We then seeked a safe place to leave the tent and our equipment during a whole day, because the bus left at 5 am to only come back as 20:30 pm. We now have our tricks and it was among the carabinieros that we asked for some help. As always here, every problem has a solution, and it required a few minutes only to the police officer to propose us the dry open garage under the building while the rain continued to fall for hours.

4:30: We quickly prepared our stuff and walked to the bus stop under a starry sky. We had an hour's rest in a very comfortable bus before arriving at the cafeteria of the mine, where we enjoyed a breakfast with the workers. Around 9:30 am, two young geologists, Victor and Franco, received us.

"Do you know that this is the only zinc mine in Chile?" They said. "The first zinc anomaly was discovered in 70’s by a prospector, but it was only in the 80’s that the deposit was discovered. Since then, several mining companies have owned it, and it is now a Canadian company, Breakwater Resources, that owns the mine."

Victor and Franco explained us the system used for exploration. Once a mineral anomaly (here zinc) was detected, the geologists made a systematic sampling of river sediments, with a frequency of one sample per km2, and a total of 50 samples. Geochemical analyses of these samples were done to determine if there was a significant mineral content. A coarse mapping was performed and the main ore anomaly was located. The second sampling campaign was more precise and focused around to the anomaly detected earlier. A sample was taken every ¼ km2, and corresponded to approximately 100 samples in total. A more detailed map could identify one or more areas with strong anomaly of ore. Finally, soil analyses were carried out by following a regular grid of 20x20 m (1000 samples). At the end of this exploratory study, the deposit was located on a map and its zinc content was known. The extension in depth of the deposit was determined by geophysical measurements (gravimetric, resistivity). Gravimetry is the measurement of the gravity field that depends on the distribution of rock density and can detect heavy minerals. The resistivity is the measurement of electrical conductivity of rocks, which depends on their chemical composition.

Victor took stones from a bag and placed them on the table. These were not ordinary rocks because some were metallic gray, others rather golden yellow. These were minerals from the deposit. Victor explained: "The gray minerals are galena, which contains lead. Yellow minerals are chalcopyrite and pyrhotite, containing copper and iron. The black mineral is blende, zinc concentrate. The zinc ore is the most concentrated in the deposit, with a content of 8%. But other metals are associated with zinc, such as iron or lead, but they are not exploited." Some of El Toqui deposits also contain gold and silver. Gold has a content of 12 grams per ton and is contained in the matrix of the rock. Then Victor told us that in the limestone, the fossils were replaced by the ore and we could see minerals that exhibit exactly the form of fossil that they replaced.

"But how was formed the ore deposit?" We asked. Franco replied: "Magmatic fluids rich in zinc and other elements rose to the surface along faults. These fluids were blocked by an impermeable rock level and interacted chemically with the rocks beneath the impermeable level. Depending on the temperature and composition of the rock, some minerals were deposited and concentrated, in particular zinc, while others were dissolved, such as calcite”.

"And how could it be decided that a deposit can be exploited?”. Victor replied that several criteria are involved, in particular the content of ore, the international supply and the cost of production. For example, in the case of zinc, currently a deposit is considered profitable if the ore contains more than 4% zinc.

Finally we asked what the role of mining geologist was. Geologists could work either in exploration or production. In exploration, the geologist must determine the deposits and their geometry at depth. It deals with sampling campaigns, geophysical analysis, and description of carrots. All data are correlated to build a cross-section or a geological profile. All data are compiled and compared in order to build a geological model of the deposit. Franco added: "The geologist has a heavy responsibility because the industrial activity of the mine depends of his work and his intuition. In addition, the mine shall ensure the economic survival of the region since the 300 people who work in the mine are from Mañihuales Villa and the surrounding areas.” In production, the geologist daily monitors of the extraction front. For reasons of safety, we did not have the permission to enter at the bottom of the galleries and we could not illustrate the work of the minors. Franco and Victor returned to their post, and we settled in the office during the afternoon until 19h, when the bus took us back to Villa Mañihuales.

The triple point (27/01/09)

Throughout January, we had the time to enjoy the landscapes of Patagonia. 1000 km in a region as fascinating leave traces and helped us to absorb the atmosphere and, I dare say, the character of this region.

But during the crossing of South Patagonia, we had the feeling of having met two very distinct characters. South of Lago General Carrera, the peaks as mythical and unaccessible as Fitz Roy and Cerro Valentin lay along the Andean chain. Those mountains are made of deep, crystalline rocks, which seem tormented and tortured, folded, distorted and recrystallised. This area exhibited no evidence of volcanism.

In contrast, north of Lago General Carrera, the landscapes and the geological character completely changed. The metamorphic rocks were replaced by volcanic rocks, some of which were very recent, as we have seen in a previous post. Moreover, from the Hudson volcano, a parade of active volcanic edifices stretches north as a string: Monte Maca, Volcan Nevado, Volcan Corvado, Chaiten and Michi Mahuida, Volcano Huequi, and Hornopiren Hualique, and the list is long to the volcan Tupungato, near Santiago. It is the southern Andean volcanic arc, segment of the "Pacific Ring of Fire”. But why is there such a difference between the north and the south of Lago General Carrera?

We interviewed Fabien Bourlon, a geologist at the Centro de Investigacion en los ecosystems de la Patagonia, in Coyhaique. Fabien explained that this difference is related to a particular global geological setting: we are just at a junction between three tectonic plates that move relative to each other (Antarctic, Nazca and South American plates). Fabien explained to us: "The Andes result from the subduction, ie the plunge, of the Nazca oceanic plate to the north and the Antarctica to the South, under the western edge of the South America plate. Very precise measurements of the movement of the tectonic plates showed that the Nazca plate moves 8 cm / year, whereas the Antarctic plate moves than 2 cm / year or less. In the case of the Nazca plate, the subduction is fast enough to generate a magmatic activity, therefore volcanism, and the seismicity is very important. In contrast, in the case of the Antarctic plate, the plunge of the plate is too slow to generate volcanic activity, and seismicity is moderate. Since we were at the junction between 3 plates, this place is called the triple point. "

You can also look at a map and compare the position of the southern Andean volcanic arc and the position of the Nazca plate and Antarctica, and you notice this coincidence. This example shows how geological phenomena observed on the surface reflect the tectonic processes on a large scale. The work of a geologist is thus the gathering of information at the surface to interpret and understand the phenomenon at a larger geological scale.

Source of figures : wikipedia

The Dams of Patagonia

Villa O'Higgins, the start of the Carretera Austral, Aysen region, Chilean Patagonia. We were in the boat that crossed the O'Higgins lake to Villa O'Higgins, the village of the end of the Carretera Austral. During the two and a half hours of crossing, a promotional video of the Aysen region was projected on a large screen. This video was followed by another video, much less professional, showing an event of hundreds of people, horse backing during several days, united behind a slogan: "Patagonia chilena ¡sin represas!" Next to the screen, a photo book, whose title was the same as the slogan, was exponed on a shelf. We looked for the meaning of "represas" in our little pocket dictionary, but it was not there, and we did not pay much attention to it.

The following day, we arrived to Villa O'Higgins, a small wild village at the bottom of a beautiful valley, surrounded by forests and snowy peaks. We found a place to camp in the garden of the hostel El Mosco and we went in the "downtown". To our surprise, we found posters at the Windows of many windows of houses and public buildings echoing the same slogan "Patagonia chilena ¡sin represas!" Back to the hostel, we found the same book as on the boat! This time, we did not contain our curiosity, and we asked Jorge, the owner of the hostel, the meaning of represas. "Dams!" he answered. This was the key to the mystery: the Chilean government plans to build huge dams along 2 rivers in the region. Opposed to this industrial project, most of the local population shows its position by hanging posters against dams: "The Chilean Patagonia without dams."

Without knowing the details of the debate, we continued our journey in an almost unknown region, but so beautiful. Long glacial valleys host beautiful rivers of blue waters full of trouts and saumons. The mountains are almost all crowned with glaciers, which produce many streams and waterfalls like large white ribbons on the shoulders of the mountains. The steep slopes are covered with cold virgin forest, from which came countless cries of exotic birds and croaking frogs. The quiet was king and we felt as absorbed in a cozy nest in this green and pristine nature. Along the road, some small farms offered campsites as well as home-made products, Duch as honey, milk and jam. By staying in one of these properties, we realized that a strong support of the Ministry of Agriculture was allocated to the rural development in agreement with a slogan as an anthem to the region of Aysen: "Aysen, Reserve Life". People are attached to the nature from which they get their resources. It was a real pleasure to return to a rural life that we had left by converting to city lifestyle.

250 km after Villa O'Higgins, we were face to face with the Rio Baker, strongly running at the bottom of a narrow and deep gorge. At this vision, we immediately understood why the Rio Baker was one of the selected sites to develop hydroelectric power: the violent current of the river channeled in a narrow gorge has an unimaginable energy potential. It seemed evident that this site could be used as a source of energy, especially since there are no homes on the slopes of the gorge. So why was there such a popular mobilization against the dams?

We found the response at Coyhaique, capital of the Aysen region, at the headquarters of the NGO “Patagonia sin represas”. We met Daniela, who had full time job for the association. During our interview, Daniela gave us important keys for understanding the problem.

- Chile is facing a major energy crisis, especially Santiago, thus limiting its economic development. The government musts respond in emergency, and the proposed dams are a source of energy at lower cost.

- The key problem is the huge distance between the production site and the consumptions site, i.e. Santiago. To overcome this problem, the project includes the construction of the longest high-voltage line in the world, crossing Chile over 2300 km.

- This line should transport continuous current so that the populations of regions crossed by the line could not benefit from the electricity, produced exclusively to residents of Santiago.

- The proposed high-voltage line should cross 4 national parks and 8 natural reserves. The lines should be hanged by 70 m height pylons and require cutting in the forest over a width of 100m for each line.

It is these high-voltage lines that are the most rejected by the local population. A communication campaign was launched on the theme "the worst image of the country," showing a photo montage of stunning landscapes from a concerned park disfigured by cables and high-voltage lines. This photo montage shows what would happen if the projects are accepted.

The debate generated around the issue of the dams spread beyond the borders of Chile. Indeed, the firms concerned for the development of the dams are European. In response, the institutions that fund the majority of the communication campaigns against dams are also foreigners, including the Natural Resource Defense Council, Greenpeace, and the millionaire Douglas Tompkins, who created the Pumalin natural park, located directly on the path of line.

Beyond the problem of Chile, that international mobilization showed and opened a real social debate by asking the important question: What will be our future? Should we opt for an industrial and economic development on a large scale, or should we favor a local development in line with our environment and sustainable development. While the region of Aysen seems supporting the latter by developing a rural tourism, the Chilean government seems rather opting for the first solution to seek to develop heavy infrastructures at the scale of the country. Another question is whether the national interest, and in priority the capital Santiago, should overpass the right of local people to choose their mode of development? Whatever outcome out of the debate and whatever the final political decision will be, the discussion is the choice of mode of development is opened. 20 or 30 years ago, it would have not been the case and the industrial development would have little opposition. We thus hope that this kind of debate can help the politics to make the right decisions.

The mural paintings (20/01/09)

In the region of Rio Ibáñez, Chile (Aysen region) and on the other side of the Andes in Argentina, were discovered cave paintings, which age has been estimated between 5000 and 10000 years. In caves, open or full, traces of hands have been painted in red!

On our way, near Cerro Castillo (Chile), we visited one of these sites declared national monument. A trail has been set up and lead to cave at the bottom of a high cliff that consisted of a thick lava flow (andesite flow). As the basis of an andesitic flow, made of scoriaes, is weaker and more porous than the main body of the flow, it is also more brittle and more easily eroded. Thus, the excavations are formed by differential erosion of the fragile basal part of the flow with respect to the erosion of the resistant body to the same flow.

It was a large mural painting that appeared under our astonished eyes. Large and smaller handprints were juxtaposed. These prints were colored in red and gave the impression that the color was projected thanks to an aerosol. In fact, the projection technique used by those men was similar but much more rustic: the Tehuelches indians used a tube filled with dye (mixed water and oxides of iron or copper) in which they blew. This is called an aerograph.

The large hands and the height at which the fingerprints were painted surprised us. We learnt that the nickname of the Tehuelche indians was the "Patagonian giants", given by the members of the Magellan expedition (sixteenth century) because of their size close to 1.80 meter.

We remained a long time in this fascinating place to imagine the scene that must occurred a few thousand years ago during these artistic activities.

Entrance in the Andean volcanic arc (15/01/09))

Since our departure from Villa O'Higgins, we had crossed a relatively homogeneous geological environment: an area where the metamorphic rocks have been distorted and transformed and where the analysis of the landscape was difficult. Metamorphic geology is not our specialty and we found it difficult to extract useful information from outcrops, and we had to focus more on the very awfull road rather than on the rocks.

That day, we had to climb the Portezuelo Rio Cañon which separates the region of Lago General Carrera and the region of Cerro Castillo. We climbed without particular difficulties and we started the descent on a comfortable road. Suddenly, at a curve, I jumped on my brakes and stopped in front of a beautiful outcrop. In contrast with the rocks we had seen so far, the rocks exhibited hexagonal columns that are typical of volcanic rocks. It was a volcanic flow, probably andesitic. After a short break, we went on.

Half an hour later, it was lunch-time, and we got our traditional bread-thuna-dulce de leche-coffee lunch. But when I turned my head to get the thermos bottle, I figured out about the nature of the gravels around us. "You saw the gravels?" I asked Caroline. "These are pumice stones." The pumice stones are very porous volcanic rocks, ejected during violent volcanic explosions. Looking around us, we then realized that the floor and the side of the road were covered with a layer of pumice. Even some laying dead trees were covered with a layer of 20 cm of pumice. The region is entirely covered! Where did these pumices come from and what were they doing here?

After lunch, we continued our descent and stopped in front of an extremely interesting outcrop: we could distinguish several layers of pumices, in white on the picture, intercallated within blacks levels. Looking at these latter, we could distinguish black holes, probably the traces of ancient roots: these levels were paleosoils. Each level of pumice corresponded to a volcanic eruption. The presence of palaeosols between each level of pumices shows that the vegetation has had the time to develop between each eruption, i.e. there was a significant time lap between each eruption. The presence of traces of plants is important to date the eruptions. Indeed, it is possible to sample these ancient roots that have grown within a level of pumice and to date them using the 14 carbon. The age thus obtained would give a minimum age of the volcanic eruption that produced the pumices. However, the most superficial pumice layer did not show any trace of colonization: the last eruption was very recent!

Fifteen kilometers later, we followed the valley of the Rio Ibañez and we ended up next to a forest of dead trees. The whole forest was dead, and the atmosphere was gloomy. The black clouds were heavy and contributed to this special atmosphere. What happened in this valley?

Thanks to a commemorative plate hanged on a rock, we finally found the answer to all our questions: in 1971 and 1991, the Hudson volcano, some tens of kilometers west, erupted. Everything now became clear: the recent volcanic deposits came from the Hudson volcano, hidden in the clouds. While we hadn’t found any trave of volcanism so far, we are now in the Andean active volcanic arc.

Later that day, we stopped at a small campsite in the farm of Rosa, a small charming woman who offered us fresh eggs, milk and other home-made products. We began a very friendly discussion with her, until the topic turned to the Hudson volcano. The face of Rosa became suddenly changed: "Nunca Mas!" (Never again).

Then she described, the fear in the eyes, the circumstances of the eruption. "At midday, the sky was completely dark and the night came. A terrible noise was heard, as if all the surrounding mountains collapsed. The ground was shaking continuously. A layer of more than 30 centimeters of ash and pumice stone fell, killing all animals and burning all plantations. We lost everything .. For 10 years, nothing has grown on the sterile soil. In the recent years only, the grass grew and it is again possible to cultivate a garden. " We were at more than 50 kilometers of the volcano ...

Then she repeated: "I do not want to experience anything as terrible as that in my life." We wish her that she indeed will not. But in our geologists minds, we were affraid of the worst for Rosa and her small farm. We knew that the Hudson volcano will erupt again and destroy the entire region. However, it is impossible to know when this will happen, and we hope to Rosa that it will be as late as possible.

Ancient and modern lakes (15-17/01/09)

Shores of Lago General Carrera, Aysen region. We left the Rio Baker canyon and passed the quiet little port of Puerto Bertrand, and we rode along the blue waters of Lago General Carrera. The lake was huge: it is the second largest lake in Latin America after Lake Titicaca. It is confined at the bottom of a valley surrounded by high mountains, some of which proudly exhibit a shiny snow cover. The waters of the lake seemt quiet and imperturbable, just little waves and jumping trouts were distinguishable. The water flows to the west in the Rio Baker, which flows into the Pacific Ocean at Tortel.

That day, we were lucky to enjoy a nice weather. Indeed, two days earlier, a rainstorm had hit the region, making our progress rather uncomfortable and wetting much of our equipment. But that day, the sun played with the clouds and illuminated parts of the surface of the waters. The lake was bounded by vertiginous cliffs falling in the waters.

While pedaling, Caroline pointed out across the lake a horizontal terrain that contrasted with the mountains. Intrigued, we continued our journey in search of other similar areas. A few kilometers later, we found these areas on our side of the lake, close to the road. These plateaus were bounded by steep slopes. By approaching these plateaus, we realized that they were made of sediments, whereas all the surrounding mountains were made of metamorphic rocks. Moreover, we noted that these plateaus exhibited very similar altitudes.

Along the road, it was possible to observe the sediments. They were quite sandy, light in color. Locally, we even saw the base of the sediments: the basal formations were deposited directly in contact upon metamorphic transformed and distorted rocks. The nearly horizontal sediments contrasted with the complex structure of the metamorphic rocks, and it was impossible to draw a continuous contact between them. This type of relationship is called an uncomformity. The fact that the sediments were uncomformable upon the metamorphic rocks indicated that there was a long time lap between the formation of the metamorphic rocks and the deposition of the sediments. The uncomformity indicated that the sediments were much more recent. However, this observation did not bring us any information on the origin of the sediments.

The answer has been given by another lake, in which flowed a river: the Lago Verde near Villa Cerro Castillo. By flowing into the lake, the river deposited sediments that formed a delta, whose surface was almost horizontal and at the same level as the lake. By analogy, we concluded that the plateaus along the Lago General Carrera were former river deltas deposited in the lake. However, given that the plateaus were 100 to 200 meters higher than the present level of the lake, we inferred that the lake level was higher at the time of the deposition of the deltas. Therefore, much of the region was covered by water. But what was the origin of such variation?

It was in Coyhaique, at the Centro de Investigacion en los ecosystemas de la Patagonia (CIEP), that we found an explanation. We met Fabien Bourlon, a geologist at the CIEP, who has worked in collaboration with glaciologists of the Institut de Recherche pour le Développement (IRD). The IRD researchers showed that the Campos de Hielo Norte and Sur were connected into a huge single mass of ice during the last glacial period. This meant that the region where the river baker flows was covered with ice, meaning that the waters of Lago General Carrera were blocked by the ice, which acted as natural dam. The waters of the lake were retained and the lake level was higher that the current level. When the ice melted, the water could flow freely into the Pacific Ocean, and the lake level was lowered to the current level.

The Carretera Austral (15-21/01/09)

The trail started in front of us, we were on the carretera austral! Mythical route for cyclists, it was completed only in 1999 when Villa O'Higgins was connected to the rest of Chile. The carretera austral was an ambitious idea of the military regime of General Pinochet who, since 1976, wanted to connect all the cities and villages of Chile by a road network. Nice idea, but when we saw the hills where the soldiers had to build the road, we were sincerely amazed! What a huge task! Moreover, they were quite proficient: the slopes were not only very strong but very long. How could blame them when you see these deep gorges carved by rivers and these innaccessible forests?

We thus began this track we heard so much about for its beauty. Approximately 200 km separated us from the next town: Cochrane. We took a small ferry to cross the fjord Michell to Puerto Yungay before struggling in a very steep uphill slope, attacked by hungry horseflies. The uphill road was long and difficult but the view was breathtaking. At the top of the mountains, glaciers and waterfalls fed streams that cut deep gorges into the rock. On the slopes of the mountains, virgin forest was full of ferns, fuchsias and other unknown plants and offered us a nature free of human activity. The descent was as steep as the climb. The road went down on the side of cliffs at the bottom of a narrow gorge that suddently opened to a wide valley where the Rio Baker exhibited large meanders. The vegetation was still very dense, and we discovered bamboos from which emerged sometimes a herd of cows. On this part of the Carretera, the passage of vehicles followed the rythm of the arrival of the small ferry and we benefited from long hours of solitude without a single engine noise ...

Shortly before Cochrane, the landscape became drier and the track became increasingly bad and loose with sand, blocks and wash board undulations. In contrast with Villa O'Higgins, the mountains were higher here and consisted of a climatic barrier. Moreover, here there are two huge ice fields (Campo de Hielo Sur and Norte) that form the Patagonian icecap, the third icecap in the world after Antarctica and Greenland.

After a little rest and a cure of fruits picked up in the garden of the camping in Cochrane, we enjoyed a heavy rain shower - which was as good as those of Normandy – and we were splashed with the mud of the puddles when we crossed buses, trucks and other vehicles ...

Again we followed the Rio Baker, but this time in a narrow gorge, until the Lake General Carrera, the second largest lake in Latin America after Lake Titicaca. All around the mountains were empty of forest but their flanks were covered with dead trunks. We met an old man who was cutting fruit trees and we asked him the reasons of all those dead trunks. "There was a fire 36 years ago," he said with an accent difficult to understand. Then he talked about the time when the Cerretera did not exist: "It was quieter before! We went to Coyhaique on horseback, it took more than a month to go there." We were about 200km away from Coyhaique and we will have 4 days to get there by bike ...

Around Cerro Castillo, the track became very bad. The wheels slipped in the loose gravels, the bicycles were violently shaken on wash board and the wind was powerfully blowing in the valley and pushed us on the side of the road. We rode at an average velocity of 5km/h even in the downhill slopes and I even stoped and pushed my bike. Disgusted, we were finally happy when we saw the paved road that marked the entrance into Villa Cerro Castillo and the end of 400 km of heavy dirt road. Along the 4-lane road, we stopped at a bus converted into snak and delightfully devoured a sandwich meat-tomato-avocado!

When we took the road again, we saw some machines working behind us: they were flatening the road we struggled with the whole morning! Now the road was flat and good! But ahead, the day was not over and we had to climb the "Cuesta del diablo" (devil's pass), the highest pass of the Carretera Austral (1120 m). We started as the evening lights shined around us. After the Chileans, this pass is particularly difficult. The road was really curved and after a few kilometers, we rode on a semi-flat road until the pass, without further difficulties. Our tough training against he wind during the first month seemed to work! The mountains that surrounded us hypnotised us by their imposing mass and their pastel pink, yellow and green colors, characteristic of volcanic rocks. The road wass empty, we went full speed and were looking for a camp.

"There is a Huemul on the road" Olivier whispered from outside the tent. I went out carefully and noiseless to get a chance to observe the symbol of the country, which looks like a deer. We were face to face ... that was the little surprise of the morning. After almost a month in the remote Patagonian nature, we quickly rode the road to Coyhaique, the capital of the Aysen region, where we have an appointment with a geologist.

The glacial moraines (31/12/08)

New Year's Eve, at the foot of Cerro Torre in the Fitz Roy massif. The tent is set up but we have not enjoyed our festive meal. The lights of the sunset inflame the peaks surrounding us, and we decide to go watching the sunset from the banks of Lago Torre. We leave the camp and we cross a field of boulders, some of which reach several meters. To access the lake view, we need to climb on top of a hill. Up there, the show is unbelievable. Cerro Torre shines on the sunset light and reflects on the waters of the lake.

But we are intrigued by the shape of the hill on which we stand: it forms a long tapered peak that is surrounding the lake. In addition, the hill is not an outcrop, but a pile of boulders of varying types and sizes. By observing these blocks closer, most bear traces of scratches, like the block that we observed in the middle of the Argentine pampas. All these blocks have been transported by the glacier Agostini that runs on the slopes of Cerro Torre and feeds the waters of Lago Torre. This accumulation of blocks is called a glacial moraine.

How to form a glacial moraine? To find out, we must understand how a glacier works. A glacier is fed continuously by snow on top of high mountains. At high altitude, the snow never melts and accumulates every year. By accumulating, the snow turns into ice and then"flows" slowly under its own weight. The motion of the glacier scratches boulders from the sides of the mountains and transport them downstream. When the glacier reaches lower altitudes, the ice melts in front of the tongue ice and the boulders contained in the ice are released just at the ice front. As this phenomenon occurs continuously, many boulders are released around the front of the tongue to form a glacial moraine. When glaciers retreat due to climate change, the moraines are isolated and form of ridge. Moraine ridges therefore mark the location and form of the ancient glaciers fronts. In the case of Lago Torre, the morainic ridge forms a natural dam and keeps the waters of the lake.

Before arriving at Lago Torre, the trail passes through several successive moraine ridges. Each ridge marks the location of the front of the Agostini glacier at a given time. While the Moraine of Lake Torre is empty of vegetation, others are more or less settled by the forest. These later are thus older. By studying the relative ages between all these moraine ridges, it is possible to reconstruct the various stages of evolution of the Agostini glacier. This type of work can be performed on any glacier, including those that no longer exist. Thus, geologists and glaciologists have been able to reconstruct the extent of the glaciers during the last period of glaciations.