The Geology of the Dolomites

After a trek, when I sit down in the corner of a mountain hut Stüa and quench my thirst with a long-awaited drink, my gaze returns to the rocky cliff walls outside framed by the window. Every time, I still feel a sense of wonder.

I also know that everyone else feels the same. It's probably been like that since prehistoric times, when man first came up here to hunt.

Whenever I walk these trails with hikers and enthusiasts, I discover how these mountains reveal their ancient history, even to non-geologists, or at least hint that their current appearance is the culmination of millions of years of history.

I remember the summers I spent working on my thesis in the Carnic Alps. When I returned to the hut where I was staying, I would lean against the stove while beside me, my rucksack with its hammer, a few chunks of rock, and my notebook all hinted at what I was doing there. The hut manager was always ready to clear up any doubts, and then the hikers would arrive with highly detailed observations and questions about the landscape they had just traversed. To me, it was incredibly beautiful how geology proved to be both fascinating and not as daunting as it initially seemed.

From a typical collection of a few beautiful pebbles or rock fragments, it's not uncommon to stumble upon ones containing fossils such as spiral or heart-shaped shells. Whatever they are, in any case they are traces of life that are universally interpreted as being marine in origin. That is undisputable; the reasons why we find them on peaks over 2,000 metres high, however, requires some reflection.

I always advise those who follow geological excursions to be a little daring with their imagination, because the further back in time you go, the more imagination is needed.

Fortunately, the brilliant minds of nature-curious geologists who preceded us, such as Giovanni Arduino, Déodat de Dolumieu, Ferdinand Freiherr von Richthofen and May Ogilvie Gordon laid the foundations for understanding the origins of these mountains. In addition, the name Dolomites also comes from scientific research, derived from the discovery of a type of rock common to many peaks in this area.

Every time I demonstrate the difference between “dolomite” and “limestone” rock with a few drops of hydrochloric acid, I am repeating the experiment by which Arduino, and later Dolumieu himself, discovered dolomite. It appears to be limestone, but it is harder and doesn't react as noticeably to the acid solution.

But let's get back to why there are shell fossils, algae, sponges, corals, teeth and vertebrae of marine reptiles, footprints of large land reptiles on fossil beaches, plant remains, drops of amber, etc. up here.

As elsewhere, intuition and observation can be very helpful and as an example I would mention Ferdinand von Richthofen. During the years when Darwin was publishing his writings on tropical islands and coral reefs, the young geologist Richthofen arrived in the Dolomites. In 1860, while he was exploring Setsass, he realized that it was a fossil reef. Setsass is similar to other Dolomite peaks, and together they form an archipelago of tropical fossil islands. Looking at the area on a map or on Google Maps, the former islands are recognizable.

Perfectly preserved islands! Entire tropical reef structures are visible in cross-section, allowing us to observe the geometry of the ancient barriers and the passages to the deeper sea. We can also admire ancient lava flows, walk on layers of volcanic ash, or search for amethysts among the lava “pillows” from volcanic events that disturbed the archipelago during the Triassic period.

Why tropical? It is because the types of fossil organisms that are found remind us of warm, tropical climates. Furthermore, it's worth remembering that until about 200 million years ago, there was only one large continent called Pangea. The Dolomite area was located roughly in the centre, offshore, or on the eastern coast.

So when wearing a warm jacket even in August and looking around... the hiker's next question is usually: how did the land mass move from the tropics to here? Living in a seismic and volcanic country at least helps us understand that the Earth is a dynamic planet. It is made up of a thin shell, the Earth's crust, which itself consists of pieces that are in constant motion. Thus, over very long periods of time, areas can migrate from South to North.

The pieces of the crust, called tectonic plates, can also collide and this is the case with the Alpine orogeny: the collision between the African and European plates raised these ancient coasts and seabeds to over 3,000 metres above sea level. The ancient sea cliffs became mountains, and this can clearly be seen when walking through the Val Badia and looking at the layers of rock that appear to have been folded as if made of plasticine.

And so the pattern becomes increasingly clear as the landscape reveals more and more of its secrets. In fact, its morphology, which is always striking to the eye of the walker, is also  another intuitive approach. The variety of landscape shapes depends on the type of rock that has been worn away over time by erosion and glaciations, while the variety of rock types depends on the environments and phenomena that have occurred over millions of years.

This is called geomorphological diversity, and we can see signs of it by looking at vertical towers, tabular plateaus, wide valleys, rolling meadows and glacial basins. Some examples? Plateaus like Puez or Fanes, isolated towers like those seen at the Cir pass and deep valleys shaped by Quaternary glaciers like Val Chedul or Val Lunga.

And so, in the warmth of the Stüa, geology becomes accessible to everyone. When looking at the landscape framed by the window, I would invite all you readers to contemplate it as if it were a painting. And if you notice any fossils or minerals along the way, or perched on a ledge in the high-altitude refuges, take a few minutes to examine them more carefully.

I can assure you that they are not “just” simple rocks...