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Tuesday, 3 January 2017

Cami de Ronda Rock Safari ...

It doesn't have quite the same ring to it as going on a bear hunt, but on New Year's Day we headed out on a rock safari around the Cami de Ronda from Platja de Sant Pol to Cala Sa Conca.

Cami de Ronda, S'Agaró, Catalonia
Cami de Ronda, S'Agaró, Catalonia


Now this is one of the prettiest bits of coastline you've ever seen. We love, love, love going for walks here, but what we hadn't appreciated is that it offers a magnificent opportunity for a geology field trip. The clever people down at the ayuntamiento - the local council - have posted a series of annotated signs on the walk explaining all about the rocks along the way. I'd noticed them in passing before, and nodded in vague agreement with the notion that they were a stellar idea, but this was the first time that we walked from sign to sign reading the story of the rocks as we went.

We kicked off on the beach at Sant Pol. This magnificent beach is one of the most beautiful in all of the Costa Brava. It's a great place to come with small children as the water is very shallow for a great distance out to sea. In the sunshine you can see many different types of particles making up the sand: black marshland sediment carried down to the bay by the streams, broken up sea shells and little sparkles of golden light from the broken up granite that makes up the coast on the Sant Feliu side of the bay. Over the years Emi and I have spent weeks of his childhood messing around in the shallows right here.

Platja de Sant Pol, S'Agaró, Catalonia
Platja de Sant Pol, S'Agaró, Catalonia

As it happens I'd noticed that there's a bothersome strip of what feels like concrete about 30 yards out to sea, which runs more or less parallel to the beach.  Well, it turns out that it's actually a fossilised deposit of sand and gravel that's been cemented together naturally by calcium carbonate deposits. From time to time they even find the odd ceramic deposit courtesy of the ancient Romans who, back in the third century AD, used to have a pottery at the far end of the bay.

Cami de Ronda, S'Agaró, Catalonia
Cami de Ronda, S'Agaró, Catalonia

The explanatory boards informed us that this part of the coastline is made up of igneous rocks.

In the Palaeozoic there were a great many volcanoes hereabouts. Most of the local rocks were formed around 253 million to 288 million years ago, when magma from these volcanoes cooled fairly slowly inside the earth's crust to form plutonic rock. The predominant rock on this stretch of the Cami de Ronda is granodiorite, which is a pale grey colour with large(ish) crystals. Often there are enormous crystals (of up to 10 cm in length), which have a different colour. They were formed from other mineral inclusions in the original magma.

Cami de Ronda, S'Agaró, Catalonia
Large crystal inclusions in the Cami de Ronda granodiorite

Oftentimes the granodiorite is crossed with seams - or dikes - of similarly coloured hypabyssal rocks, such as porphyry granite, which is of a very similar colour. They formed after the original granodiorite had cooled, hardened and fractured. Fresh magma flowing into the fractures in the original rock cooled more slowly, and as a result the crystal structure of these parts is notably different - smaller and more finely grained.

Cami de Ronda, S'Agaró, Catalonia
Cami de Ronda, S'Agaró, Catalonia

On the ayuntamiento's diagram below you can see the plutonic rocks, such as the granodiorite shaded pink. They cooled quite slowly in the earth's mantle forming larger crystal structures as a resut. The hypabyssal rocks, such as porphyry granite, are shaded red and shown as channels of magma cooling rather more quickly in the fractures in and around the original granodiorite, and hence forming different crystal structures.



Cami de Ronda, S'Agaró, Catalonia
The ever-present herring gulls enjoying a granodiorite perch


Cami de Ronda, S'Agaró, Catalonia
Cami de Ronda, S'Agaró, Catalonia

Along the walk there are various walls built of other materials. There's limestone in the walls that make up the Senya Blanca Villa, and the Glorieta gazebo that comes from quarries near Banyoles, and there's rich red granite that comes from a quarry on the other side of our village, Sant Feliu de Guíxols.


Cami de Ronda, S'Agaró, Catalonia
Cami de Ronda, S'Agaró, Catalonia

Everyone seemed to be out enjoying the sunshine, and making a healthy start to their New Year.

Cami de Ronda, S'Agaró, Catalonia
Cami de Ronda, S'Agaró, Catalonia


Cami de Ronda, S'Agaró, Catalonia
Cami de Ronda, S'Agaró, Catalonia

Cami de Ronda, S'Agaró, Catalonia
Cami de Ronda, S'Agaró, Catalonia

Cami de Ronda, S'Agaró, Catalonia
Cami de Ronda, S'Agaró, Catalonia


Cami de Ronda, S'Agaró, Catalonia
Cami de Ronda, S'Agaró, Catalonia


Cami de Ronda, S'Agaró, Catalonia
Cami de Ronda, S'Agaró, Catalonia

Cami de Ronda, S'Agaró, Catalonia
Cami de Ronda, S'Agaró, Catalonia

We went down to the Cala Pedrosa (Stony Cove) to have a closer look at the rocks down there. Much of the material on the rocky beach has been rounded and worn smooth by the great spin-cycle of the sea, and the unrelenting action of the waves. We admired many large crystals in the granodiorite where there had been sold inclusions in the original magma as it cooled. We also saw a number of veins of hypabyssal rock formed by later magma penetration of fractures in the original granodiorite.

Cala Pedrosa, Cami de Ronda, S'Agaró, Catalonia
Cala Pedrosa, Cami de Ronda, S'Agaró, Catalonia



La Glorieta, Cami de Ronda, S'Agaró, Catalonia
La Glorieta gazebo, Cami de Ronda, S'Agaró, Catalonia

La Glorieta, Cami de Ronda, S'Agaró, Catalonia
La Glorieta gazebo

We watched other people taking photos. It's such an obsession these days - not that I can talk!

And sitting down on a rock, away from everyone, we spotted this handsome cormorant. Isn't he magnificent? I'm pretty sure he's a Great Cormorant.

Great Cormorant, Cami de Ronda, S'Agaró, Catalonia
A Great Cormorant, Cami de Ronda, S'Agaró, Catalonia

He also seemed to have been suffering from the excesses of the night before. As I watched he had a great big yawn, which gave me a wonderful view of the sweep of his hook-ended beak.

Cami de Ronda, S'Agaró, Catalonia
Great Cormorant, Cami de Ronda, S'Agaró, Catalonia

And this, I believe, is a juvenile Herring Gull. We've got thousands of these chaps up and down the Costa. Someone told me that they tend to mate for life, although there is the occasional divorce, which carries social consequences for the divorcing partners who tend to get shunned a bit by the rest of the colony.

Juvenile Herring Gull,Cami de Ronda, S'Agaró, Catalonia
Juvenile Herring Gull, Cami de Ronda, S'Agaró, Catalonia

Our walk ended at Cala Sa Conca, where a glorious sandy beach has formed without any rivers or streams entering the sea. Much of the sand on this beach have been washed here by the currents from the neighbouring Platja d'Aro beach. Some has also resulted from sea erosion of the cliffs that surround the beach.

Cala Sa Conca, Cami de Ronda, S'Agaró, Catalonia
Cala Sa Conca, Cami de Ronda, Catalonia

There's a bit of a tradition here of having a first dip of the year on New Year's Day. A number of valiant souls were braving the chill of the sea for their first swim of 2017. At this time of the year, whilst the air temperature is fairly benign, the water is very cold. We were happy to watch. 

And then these chaps caught my eye on the rocks at the other end of the beach. More cormorants! Aren't they impressive?

Great Cormorants, Cala Sa Conca, Cami de Ronda,  Catalonia
Great Cormorants, Cala Sa Conca, Cami de Ronda, S'Agaró, Catalonia


All the best for now and best wishes for a very happy 2017!

Bonny x

2 comments:

  1. Oh, Bonny, how I wish I could take a walk there...I love rocks, and I love those trees. Or maybe it is the mood I feel they create. Whatever, I enjoyed this post a lot.

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    Replies
    1. I love the shapes and the shadows of the Costa Brava pine trees too. They're just so dramatic. Thank you for stopping by, Bonny

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