8 comments on “Volcanoes where we don’t expect them – GARROTXA VOLCANIC FIELD, NE Spain

    • Hi dawmast, no, there aren’t. The basalts and basanites are the only products mentioned in all papers I’ve seen (“…range from strongly silica-undersaturated to nearly silica-saturated compositions”). So no saturated or oversaturated magmas. And these are fairly homogenous throughout the whole Catalan VZ, even throughout the rest of Europe (for this rift system). Except for a few volcanoes containing even ultrabasic xenolits, which are thought to come from the parent magma.

      The explanation is that in a monogenetic field like this, volcanism moves on after a time. There are no shallow magma chambers where magma would accumulate, sit and evolve until the next eruption. Magmas here come directly from a source in the crust-mantle boundary, ~30 km deep.

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      • On the other hand a similar volcanic field, the VulkanEifel in southwest Germany has erupted evolved phonolite magmas in the Laacher See region. Why did magma accumulate in magmachambers there and has it to do with the Neuwied Basin and the Lower Rhine Graben?

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        • Yes, interesting question. I guess this is a case of no two volcanoes (or fields) ever being identical. Even though both the Garrotxa and the Eifel fields developed in the overall context of the CER, the local conditions are quite different – even within the parts of the Eifel VF. There are always two questions to look at: (1) where does the magma come from, and (2) why did it erupt just where it did?

          In the WestEVF magmas erupted in uplifted parts of the Rhenish Massif (in the Eifel N-S graben zone). EastEVF (Laacher See) lavas erupted in the down-faulted Neuwied basin. Also, the EastEVF is affected by the Siegen thrust zone, which may have caused deviations in dike orientation. If a dike is stalled, it may develop into a sill and/or accumulate in another shape of magma reservoir. So, the rifting and faulting in connection with the Alpine Orogenese must be the general answer to (2) for all the European monogenetic fields.

          As to (1), the mantle plume present below the Eifel should play an important role in the Eifel fields. It is thought that wide magma collection zones exist under the Eifel VF. Above such zones stacked magma chambers could have developed. That would explain more evolved lavas being erupted in the center of the fields. The Laacher See did have a magma chamber at 6-8 km depth. It also had a “strongly compositionally zoned and highly evolved magma column”. Still, most of all lavas in the Eifel are mafic, with only rare intermediate and local small highly evolved centers in the eastern central part of the field.

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          • Does the VulkanEifel volcanic field have a high potential for exploiting geothermal energy, I think especially the Laacher See region with its cooling magmachamber. Is Laacher See expected to erupt again in the (near) future?

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  1. It is about a year since our M 7.1 earthquake in Anchorage. The felt aftershocks have mostly stopped. Link to an insert we get from our natural gas company, Enstar. One of the road collapses moved a couple of their natural gas pipelines 13′ from their original location. There was a 6″ main pipeline made of plastic and a 4″ steel transmission pipeline. There were no leaks and no breaks in service. Sometimes we get the engineering right. Sometimes we just get lucky. Is generally best to be both. Cheers –

    Click to access November-2019-web.pdf

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  2. What a fascinating article, thank you! I had no idea any part of Spain was volcanic. Something to look at whenever I get there. Thanks!

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  3. Pingback: Garrotxa Volcanic Zone Hike - A walk and a lark

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