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Poços de Caldas, in Minas Gerais, is a famous hydromineral resort and, for many, a surprising Brazilian city on top of a volcano ancestral. Discover its geological secrets!
The idea of a Brazilian city on top of a dormant volcano arouses curiosity and, for some, even a certain fear. And what if we tell you that not only does this city exist, but it is also known as Poços de Caldas, in Minas Gerais, famous for its therapeutic waters? Many visitors and even locals may be unaware of the geological grandeur beneath their feet.
Science reveals to us that this Brazilian city on top of a volcano rest, in fact, over an immense volcanic caldera that has been extinct for tens of millions of years. Let's uncover the fascinating history and characteristics of this unique formation.
Poços de Caldas: a geological wonder and a unique Brazilian city on top of a volcano
Located in the southwest of Minas Gerais, Poços de Caldas is nestled on a mountainous plateau, but its most striking geological feature is a vast circular depression – the volcanic caldera. This caldera is the geological heart of the region, a ring of mountains known as Serra de São Domingos. The Poços de Caldas Alkaline Complex is one of the largest intrusions of alkaline rocks on the planet, with a diameter ranging from 30 to 35 kilometers and an area of approximately 800 km², being the second largest alkaline massif in the world.
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It is essential to understand that this Brazilian city on top of a volcano does not occupy a conical structure like Mount Fuji. This is a boiler, a much larger depression formed by the collapse of an ancient supervolcano after colossal eruptions or by the emptying of a large underground magma chamber.
Journey to the deep past: the origins of the Brazilian city on top of a volcano
The formation of the Poços de Caldas Volcanic Complex occurred a considerable time ago, between 72 and 90 million years ago, in the transition from the Cretaceous to the Cenozoic periods. It was a complex geological process and long, involving the rise of a large volume of alkaline magma from the Earth's mantle. This generated intense volcanic activity, with lava flows (mainly phonolites) and explosive eruptions. The climax was the collapse of the structure, forming the vast caldera that we see today.
Crucially, the volcano beneath this Brazilian city on top of a volcano is classified by scientists as extinct, and not merely dormant. This means that it has not erupted for tens of millions of years and there is no scientific expectation that it will return to activity. This long inactivity is a determining factor in the safety and type of development that has occurred in the region.
Treasures of the Caldera: the rich heritage of volcanic activity in Poços de Caldas
The volcanic heritage of Poços de Caldas is vast and valuable. The famous thermal waters are undoubtedly the most emblematic natural resource. These waters are, in their origin, meteoric (from rain) that infiltrate deep underground through fractures. During their long journey, they are heated by the Earth's natural heat and interact chemically with the alkaline rocks, emerging with unique characteristics: hyperthermal (between 40°C and 44°C), alkaline pH, and rich in sodium bicarbonate, sulfur, fluorides and a slight natural radioactivity (radon), known for their therapeutic properties.
Beyond the waters, this Brazilian city on top of a volcano has a remarkable concentration of minerals. The region is home to extensive deposits of bauxite, explored by Alcoa; it was home to the first mine of uranium of the country (Osamu Utsumi Mine); and has occurrences of thorium, zirconium (including caldasite, named after the region) and important Rare Earth Elements (REE).
Development and challenges of a Brazilian city on top of a volcano
The development of Poços de Caldas was initially driven by its thermal waters, with the arrival of the railway in 1886 catalyzing its growth as a renowned hydromineral resort. The city has demonstrated great resilience throughout its history, diversifying its economy through the exploitation of its mineral wealth and industrial development, especially after the prohibition of gambling in the 1940s, without ever abandoning its thermal tourism vocation.
However, urban planning within a volcanic caldera presents unique challenges for this Brazilian city on top of a volcano. It is crucial to reconcile growth with the protection of water resources, especially the recharge zones of thermal aquifers, and to mitigate geological risks such as landslides and floods, especially on steep slopes.
Embracing the volcano: tourism, culture and the unique identity of Poços de Caldas
Poços de Caldas has managed to transform its extraordinary geological heritage into a pillar of its tourist and cultural identity. “Rota Volcânica” is an initiative that promotes tourism in the region, exploring rock formations, viewpoints with panoramic views of the caldera and, of course, the hot springs, all under the fascinating narrative of being a Brazilian city on top of a volcano.
Local culture is inseparable from its waters. The architecture of spas, such as Thermas Antônio Carlos, and the tradition of therapeutic baths are central. Although popular perception may simplify the geology to a “dormant volcano,” institutions such as the Poços de Caldas Historical and Geographical Museum seek to educate the public about the formation of the extinct caldera. This rich geological context offers a immense potential for geotourism and geoscientific education.
Now I understand the name Poços de Caldas…
Super interesting!!
Seen on Google map, using the relief function, it looks more like the impact of a large meteor.
Its crowning is higher to the west and lower to the east.
I live 40 km from Poços de Caldas.
I also imagine that this caldera, with a diameter of 35 to 40 km, was the result of a huge meteor impact.
It is inconceivable that the circumference of a volcano's mouth reaches 40 km.
Poços de Caldas is located on the edge of the crater to the north and my city of Andradas is on the edge of the other edge but “OUTSIDE THE CRATER” to the south, at a distance of 40 km between the two cities.
I believe that a volcano would not create a crater of these dimensions.!!!!!
Your perspective of reasoning is acceptable and ponderable, suitable for other analyses, by those who seek to obtain a doctorate in research! Unfortunately, we are heirs of a nation that, throughout the years and history, has always imposed truths that contradict the obvious, as a clear example, our own ethnicity, in several regions, has been nullified!
We are talking about THOUSANDS OF YEARS ago. In this “short period” (contains irony) many changes occurred. Including the circumference of the volcano’s mouth.
Yellowstone Park in the US is also a volcano whose shape is similar to Poços de Caldas. To have an astrobleme the size of the Poços crater, it would have to be a giant body that would cause devastation on the scale that caused the extinction of the dinosaurs.
Guarulhos in São Paulo is also part of a dormant volcano and just look at the geography of the city from above and you will see that we are inside a crater.
Guarulhos is located in a region hit by a meteorite. In other words, it is an impact crater. An astrobleme. Poços de Caldas is a volcanic caldera.
The Astroblema is in Parelheiros, not in Guarulhos.
Guarulhos is next to the Serra da Cantareira, it is not a circular crater. In this region, the only similar event is in Parelheiros, where a meteorite fell.