Wednesday August 30th, 2017

Stage 11Lorca / Observatorio Astronómico de Calar Alto

Start 12h28 (Local time)
  • Fernando Escartín commentary

    Mid-mountain, with an uphill finale. A day with a 3,434-metre slope that can result in significant differences to the general classification and begin to hint at a possible winner. The final mountain pass is a long one, but not excessively difficult, and it will require consistency in order to conquer Velefique and Calar Alto, two back-to-back 1st category climbs.


Plasters and planets

Cocedores Beach © TM Grupo Inmobiliario / Attribution 2.0 Generic (CC BY 2.0)Plaster crystals and the Pulpí Geode, Almería © Luis CarcavillaCalar Alto Astronomical Observatory © Digigalos / Creative Commons Genérica de Atribución/Compartir-Igual 3.0Tabernas Desert, Almería. © Roy Luck / Attribution 2.0 Generic (CC BY 2.0)

Lorca - Calar Alto Observatory

All over the Mediterranean coast, we can see the contrast between the coastal plains and the inland mountain ranges; in Lorca the contrast is enormous because a large system of very active and very clearly defined faults separates the plains from the mountains. This contrast is also obvious in the 3D diagram, with the grey Quaternary colour contrasting with the large variety of colours on the other side of the fault.

The peloton starts its adventure near Lorca (Murcia) and heads towards the coast. If there were to be an underground stage, it would have to be this one, so that we could see one of Europe's most prized geodiversity jewels, the Pulpí Geode. A geode is a sealed rocky cavity where the minerals contained in the fluids that flowed inside the rock thousands of years ago have become crystallised. The most common geodes are only a few centimetres in diameter and are sold all over the world, but the Pulpí Geode is 8 metres tall and houses transparent gypsum crystals measuring up to 2 metres. It also stands out for being the only geode in the world that can be visited, thanks to the atmospheric conditions found inside it (20ºC, with an acceptable humidity level).

Also at Pulpí are the Honduras cliffs, closing off Cocedores Beach. The Palomares Fault can be seen on the cliffs. It is a fracture that goes from North-East to South-West that links volcanic rocks to marine sandstone.

But, without a doubt, the stage's main protagonist is the karst landscape of Sorbas. A karst is a form of relief that is created when water dissolves and erodes soluble rocks (limestone, gypsum, halite, dolomite, etc.). If the geological modelling takes place on the surface (exokarst), sinkholes, canyons and limestone pavements are formed. If the processes takes place underground (endokarst), caves, galleries and subterranean streams are formed. The most spectacular karst systems happen on limestone rocks, while those that happen on gypsum are, generally, less so. The karst of Sorbas formed 6 million years ago, on gypsum, but features over 1000 interconnected caves. The stalactites, stalagmites, speleothems and other crystalline formations found inside it create amazingly beautiful landscapes and are, to many, one of Andalusia's most cherished relics.

Worth mentioning in the final part of the stage is the Tabernas Desert, in Almería. If the peninsula's South-East has a semi-arid climate, two of the Baetic mountain ranges, Los Filabres and Alhamilla, surround the area of Tabernas and prevent rain from falling there; it is an example of a microclimate that has been conditioned by reliefs. The climate there is extremely arid and vegetation is rare. With dry and unprotected ground, the rare precipitations that do take place have an enormous erosive capacity and are responsible for creating the region's dramatic landscapes, full of gullies, watercourses, canyons, collapses, crashes, active and abandoned meanders, etc.

The Calar Alto Astronomical Observatory, this stage's finish-line, is found in Los Filabres Mountain Range, at an altitude of 2168 metres above sea level. It is one of the largest observatories in Europe, and features 3 microscopes through which the wonders of the universe can be observed, like its last great discovery, the asteroid 2009 DS36.

Stage Term: Gypsum

Gypsum is a mineral composed of calcium sulphate (CaSO4·2H2O) whose formation has a chemical origin based on the evaporation of oversaturated aqueous solutions in shallow lakes or seas. This mineral is the hydrated phase of a total of 3 possible varieties. We can also find the anhydrous phase, known as anhydrite (CaSO4) and the semi hydrated, known as basanite (CaSO4·½H2O).

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