Interview with a Geologist

 

PART 1

 

The spectacle you can enjoy watching from above the Larian region is really astonishing for its natural beauty and grandeur. My first curiosity is linked to the strange shape of this lake, an inverted Y, which is not common. Moreover the only outflow of the river is located by the side of Lecco, why?

 

Good question, geologists like me have studied a lot to answer it. The latest scientific evidence has shown that the so called “paleoadda” flowed into the branch of Como. Between Bellano and Bellagio there was a rather big rock and the river couldn’t go over it. To the south of this rock there was a smaller river which conveyed the waters of the mountain streams coming from the area now called Valsassina, and flowing towards the plain. At that time there were only rivers and not a lake.

 

PART 2

 

Very interesting. Tell me more, which were the most important events that have changed the situation?

 

In the geological history of this area several periods followed one another, the events which shaped the region we see today, date back to at least 200 million years ago. But in order to avoid difficult words used by insiders, I will draw your attention to the most important events, so we get straight to the point you are interested in. There are 4 events of primary importance:

 

1 - First of all you should know that most of the mountain surface we see today formed on the seabed, at the time called Tethys: skeletons of shellfish laid down on the seabed and, over time, formed thick stratifications. These stratifications came to the surface and reached a considerable height and at the top of the mountain you can see some rocks with fossils, you don’t expect to find there.

 

Do you mean we are on a mountain which formed in the sea? this first event is already incomprehensible to me, but let’s listen to the second one! I’m all ears!

 

2 - Here is the second one: You should know that the erosional power of the rivers increased a lot when a terrifying event happened. When the Straits of Gibraltar suddenly closed, the Mediterranean sea in that time got dry, as it were. The rivers hollowed out the canyons, which we find today under our lake and which give to Lake Como the distinction of being the deepest among the Alpine lakes. You knew it. Didn’t you?

 

Yes this isn’t new to me, 410 Mts deep, as our teacher at the primary school made me study. But go on, please. What should be the third important event?

 

3 - The third event is the collision of the African and the Eurasian tectonic plates, as a result Orogeny took place, that is to say the Alps arose. The impact among the continents, due to the pushing magma under the earth’s crust, moved and twisted the rocks, also the ones under the sea, arising them to considerable heights and the sediments on the surface slid one over the other.

 

I see, we walk on rocks which were born in a distant time and space. You made the story short, but I imagine it took hundreds of thousands years, geological eras, didn’t it?

 

4 - Of course, a very long time during which a lot of moulds were left. The fourth and crucial event: the quaternary glaciation enabled the development of powerful lobes which eroded the mountains and dragged a huge quantity of drifts towards the plain. The baseline of the mountain turned into a wide basin capable of containing the present lake. Probably the ice pulled down the rock formation, which we could see today between Bellano and Bellagio. The river, which started to flow after the ice Age, found a wider space in the basin of Lecco and thanks to more favourable slopes, the outflow of the river changed its direction running towards Lecco.

 

PART 3

 

You told me about events really unthinkable for a hiker like me, but really enchanting and upsetting. The earth must have been really inhospitable in some periods of its long history.

I wonder if in the future we can resist the force of nature….

 

Well, back to our subject. Now I know what you do as a job and what I can ask you, can you tell me why the lake narrows just near Lecco?

 

It’s due to the three rivers of the town and to the debris they piled up over the centuries. In this way the inhabitants of the ancient village could build the first bridge to link up the two sides of the lake. And each village on the lakeside was built on the warps of the rivers that flow to the the present Lake. And now they are an integral part of the landscape you see.

 

That’s true. Nature and human beings are as one, even though nature still prevails. It’s not so obvious from the town, you need to arrive here to realize it.

Thank you Mr Valsecchi, I have learned a lot of interesting things, absolutely new for me.

 

My pleasure! If you want to go into this subject, visit the web page and download the geological history I wrote just for you and for the most attentive hikers.

 

 

 

 

 

INTERVIEW TO A GEOLOGIST - PART 2

 

Good morning. Mr Geo. I was told I can ask you a question. I would like to start immediately, I have a lot of curiosities.

 

I’m pleased to listen to your questions.

 

1 - What’s the name of the rock we are walking on right now?

 

This area, called “Bocchette di Moregge”, is situated at the shift point between two outcropping geological formations: The formation of the Dolomia Principale and the formation of limestone ZU. They are strange names, aren’t them? For you and for those who are listening to us, I’ll call them in a friendly way DP and CZ, is it ok?

The difference between them is not so clear, but the landscape helps us: the area with the most gentle shapes is made of CZ limestone ZU, while the more rugged shapes, the outcropping stones on the side of the path towards mount Moregallo, are made of DP, the Dolomia Principale.

 

2 - Fine thanks! I think I have understood. But which is the oldest of the two formations? Where did they form and how can I get this information?

 

The Dolomia Principale is the oldest one and it doesn’t contain fossils. The limestone ZU is more recent and is rich in fossils. They both formed in the sea, in the area of the carbonate shelf.

The DP is a deposit of a peritidal platform, this means it formed in a flat shallow sea. It was then strongly dolomitized which prevented the conservation of fossils and other aquatic organisms.

On the contrary the CZ formed on a carbonate ramp, that’s to say an inclined platform, in a quite deep sea. and contains a lot of different types of fossils.

 

3 - What kind of soil forms on them and what kind of plants can we usually see?

 

The DP usually forms quite rugged landscapes, because it is rigid, not very deformable, for this reason it tends to fracture easily and to build varied shapes such as ridges, picks and crests. In this case we talk about a dolomitic landscape, which comes from the rigidity of lithology. The soil on them is usually poor and barren and tends to build colluvia, screes.

 

The soil made of limestone decay of ZU is richer, finer and more fertile. This formation can’t be seen easily because of a big stratum of decay which creates grass and wood. Their gentle shapes often contrast with the dolomitic landscape.

 

In any case, the CZ above 600-800 meters of altitude is covered by few groves with short or middle height trees: durmast, hazel, beech and birch, at a lower altitude the beech disappears and chestnuts and ash trees grow.

 

The minerals which generally form the Dolomia Principale are mainly dolomite MgCa(Co3)2 and calcite.

 

4 - Are these stones used in a particularly application?

 

The limestone Zu isn’t particularly used, while the Dolomia Principale is locally used by quarries. They break them and sell the product called “Moregallo” to building companies. At the base line of Mount Moregallo there are still mining companies. Some ancient mining activities date back to 1800 and were situated at the baseline of Mount Moregallo in the area called “Sassello Tecion”.