Eifel Volcanic Field I

Few volcanic areas in the world are as easily accessible and in such a friendly environment as the Eifel Volcanic Field. Volcanophiles generally know of the existence of this volcanic field and that it lies somewhere in western Germany. Most ordinary people however have no idea that an active volcanic field with some 200+ volcanoes is located in western Germany, some 25 km from Belgium, 50 km from Luxemburg and 80 km from The Netherlands.

Lush, green, easily accessible and previously quite dangerous. The Shire might have been here before. Image by author.

The field is generally located around the towns and cities of Hillesheim, Gerolstein, Daun, Mayen and Koblenz. The world-famous racing circuit of the Nürburgring (Nordschleife) actually lies around and in between a few volcanic cones, of which the “Hohe Acht” is the most famous one because it’s also the highest point in the Eifel hills.

If you believe some of the more sensation oriented media, you will be led to believe that the Eifel is actually an inflated supervolcano, which has already shown its potential at Laacher See (one of 2 caldera features in the volcanic field) and is just waiting to end civilization as we know it anywhere between Scandinavia, the UK, Spain and the Balkan countries. We’ve all read those articles and wondered if 99% or 100% of it was made up on the spot.

In fact, volcanic activity in the Eifel Volcanic Field has been almost exclusively monogenetic, leaving scoria cones, tuff rings, lava flows and maars scattered over the hills since about 700.000 years ago. The Eifel is the type locality for “maars”, so activity like this all over the world is named after the volcanic lakes in these hills. On one occasion, a significantly larger (one of the most recent) eruption occurred, which left the Laacher See caldera. The good thing about all this activity is that there are a lot of volcanic features to visit and they are almost all very easy to reach. No mountaineering skills are needed and no supplies need to be carried because all this is in the middle of the civilized world.

Scoria cone hidden in the trees in the middle of a field. No guided tour needed here. Image by author.

Once you reach the crater area, you suddenly realize this is the real deal, even though the surroundings don’t look like it. Image by author

The “Vulkanmuseum” in Daun is worth a visit if you have some spare time. A lot of things are explained and a lot of good information is provided. This too can be said about most volcanic features in the Eifel. At many cones and maars you will find information signs with tons of useful information about the volcanic feature you are visiting.

Of special interest are the cold-water Geysers that are found in the Eifel. They are not driven by heat, but by CO2. The CO2 escaping from the magma sources below the Eifel dissolves into the groundwater at some places. Whenever the amount of dissolved CO2 reaches a critical point, bubbles start forming, lowering the hydrostatic pressure of the underlying water, triggering the formation of more bubbles etc etc. This chain reaction, when combined with a ‘conduit’ leading to surface, is what drives the geyser, until enough CO2 has been released to restore the stable situation again. The one in Wallenborn (Geyser Brubbel) is quiet for about 35 minutes and ejects cold water for about 2 minutes. Almost perfect for a visit! The one in Andernach is actually the world’s highest cold-water geyser. If you cannot go and visit them there, just buy a bottle of Gerolsteiner water to play Volcano at home. This world-famous mineral water is extracted from a drilled well and is naturally carbonated by the volcanic field. Shake the bottle firmly, open the cap and you have your own Eifel Coldwater Geyser at home.

If you happen to be a big beer fan, you might want to visit the Vulkanbrauerei (Volcanobrewery) in Mendig, close to the Laacher See. They produce and sell various beer specialties and have a very cool underground cellar (felsenkeller) open for visitors, that is cut out of columnar basalt, which they claim is the deepest beercellar in the world. It certainly sounds awesome to have a huge cellar to keep your beer cold, cut out of columnar basalt underneath/inside an old lava flow.

Already a nice place for a swinging chair. Once you know of the maar below and the scoria cones in the distance, it suddenly gets even better, especially if you took your beer from the Vulkanbrauerei. Image by author.

If you ever happen to be near the Eifel and have a spare day or so, I think this area is definitely worth a visit. Don’t expect any huge and spectacular volcanoes, dangerous trips or much live activity, because most features are quite hidden and somewhat influenced by erosion. The area is kind of like the old Petting zoo of the volcanic realm with some very cool animals in it.

A group of German Crater Deer having a good time inside an old volcanic crater. Image by author.

In part II, chryphia will give some more info on the Eifel Volcanic Field in a follow up post. Thanks to chryphia and Spica for helping out on this one!

El Nathan

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Name that Volcano Riddle ……

 1 volcano 1 point

 

During the 1960s ‘cold war’, a discovery in a cavern under this volcano raised the spectre of an impending rocket attack …. SOLVED

Talla 1 point for Shinmoedake – some scenes from the 1967 You Only Live Twice were filmed on locationn at this volcano! (Spectre’s rocket base!)

Kilgharrah

Urban volcanism!

The ironically named Mount Eden, near downtown Auckland.

Most people in the world agree on one thing: it is safer to live far from a volcano then it is living right on top of it. Living next too, or on top of a volcano is like sleeping in a cave with a friendly bear. Sure, it has it’s advantages, you stay nice and warm, you don’t have to worry about other predators, a good part of the year it is nice and quiet, but still….. you know that some day he will grab you and eat you. The inhabitants (some more permanent than others) of Herculanum, Pompeï, Heimaey and the Hawaiian Royal Gardens have found out the hard way.

New Zealand is, apart from being stunningly beautiful, one of the least populated countries in the World. When Western settlers arrived they could have chosen any location to go and build large cities. For some reason however, the inhabitants found it neccesary to build their largest city directly on top of a volcanic field with about 50 scoria cones, maars and tuff rings dotting the landscape. I suppose the knowledge of volcanism was not as developed back then as it is today, but nevertheless it is quite unfortunate.

Photograph by Mollivan Jon. Mount Taranaki.

New Zealand is dominated by subduction volcanism, with famous Mount Taranaki (or Egmont) as one of the most visually stunning stratovolcanoes in the world from both the ground and above, and with the infamous Taupo Volcanic Zone, best known for being one of the worlds “super” volcanoes. At 250 km from Auckland this is already quite a hazard on itself.

The Auckland Volcanic Field is a monogenetic volcanic field, meaning that an eruptive episode only happens once through a vent. Each eruptive episode generates a new vent somewhere within the volcanic field as opposed to “normal” volcanism where a volcanic vent has succesive eruptive episodes causing a volcano to build up and blow up occasionaly. The Auckland Volcanic Field produces basaltic scoria cones, maars and tuff rings (with the exception of the island of Rangitoto which erupted several times). All three are caused by the same type of magma, basaltic magma in this case, but the location the surface penetration, the eruptive flowrate and the total volume of the basalt determine the type of surface expression. The volcanic field has been active for about 150.000 (0.15M) years now. Older volcanic fields are found towards the south; South Auckland (1.5-0.5M), Ngatutura (1.8-1.5M) and Okete (1.8-2.7M).

The source of the basalt is not quite clear however. Basalt is normally not associated with subduction volcanism. Petrology and earthquake data have practically ruled out the possibility of the lava having an origin in melt generated by the subducting Pacific Plate. The Auckland volcanic field also sits some 200 km behind the active volcanic front of the Taupo Volcanic Zone. Furthermore, there is no evidence that the subducted Pacific plate reaches all the way to the Auckland volcanic Field.

Basalt is usually associated with mid-oceanic ridges/spreading centers or hotspot volcanism. Again, petrology has not been able to find much evidence for hotspot volcanism either. Additionaly, the propagation of the volcanic fields is directy opposite to the relative motion of the plate; the oldest volcanic field should have been in the north and the youngest in the south if a hotspot or mantle plume was involved. It is possible that the complex geology with major plates subducting, twisting and turning in the area is causing localised decompressional melting , leading to magma migration upwards right below the city of Auckland. There is some extention ongoing in the area, so this seems like a plausible explanation.

The Pacific plate and the Australian plate in a complicated geological setup

This image shows the subdution margin, the strike-slip faults to the southwest and extention(volcanic back-arc) to the northwest of the subduction margin.

Monogenetic volcanic fields are very interesting and highly unpredictable. The eruptions are not very large or extremely violent, but they can occur pretty much anywhere within the field at any time. With a large city with hundreds of thousands of inhabitants spanning the field, this is exactly what you don’t want. Paricutin in Mexico is the most famous example of this type of volcanism. One day you are happily working your crops, the next day you have to flee from your land because a volcano decided to take over your land. Bad luck, deal with it. Any new eruption within the Auckland Volcanic field will have as much compassion with buildings, streets, highways, parks and emergency shelters as Paricutin had with the crops that were growing there. This is what makes Auckland a relatively dangerous place to live in because it is not clear how much warning time there will be and how accurately the location of an eruption can be predicted with modern equipment.

The reason why new volcanoes pop up at random has to do with the generation of the magma. It is important that the generation occurs very slow. Slow enough to be unable to build a plumbing system that would efficiently conduct the magma to surface. Every new, hot, fresh slug of magma finds it’s own path to the surface, erupts and that’s it. The conduit cools and is no longer usable for the next slug of magma that arrives several decades or hundreds of years later below a slightly different part of the volcanic field. There is not enough magma flowing into one area to create a magma chamber in which the magma can evolve and produce more silicic types of magma.

Ridiculous in Los Angeles, not so ridiculous in Auckland. Bring out Tommy Lee Jones!

We have all seen the Hollywood movie “Volcano” and no doubt that many Los Angeles citizens have had a very good laugh at it (the La Brea tar pits are the surface expression of a leaking oilfield through a fault, it has nothing to do with volcanism whatsoever), but for the citizens of Auckland, those images are not even very far from the truth. The past gives an excellent example of what can happen. The next eruption in the field will most likely follow this scenario:

1 – Magma is forced upward through weak points in the crust.

2 – Either the magma contacts ground-water, or reduced pressure near the surface causes gases to bubble out of solution. The result is a phraetic or steam-blast eruption. The heaviest material is thrown out horizontally to form a tuff ring. Lighter material is blasted vertically to form an eruptive column. After a few days, weeks or months, the volcano falls quiet. Several of Auckland’s volcanos became extinct at this point.

3 – Additional magma may rise in the conduit. If enough magma is supplied, fire fountaining starts through one or more vents. Small lava flows may be produced, which do not escape the tuff ring. Sometimes the eruptions build scoria cones.

4- If fire fountaining continues beyond this point, the scoria cones can coalesce to rise and bury the tuff ring. Lava flows can also fill the surrounding valleys.

5 – Sometimes the outflow of lava is so great that it undermines the cone, which collapses into the flow and is carried away, leaving a horseshoe-shaped breached crater. If lava flows for long enough, nearby valleys are totally filled in and the lava floods the entire area with a large sheet.

Isn’t that just wonderful right in your own neighbourhood?

Map showing the city of Auckland and the eruptive centers.Pick your favourite spot to build your house.

The big question that remains is then: When is the next eruption going to be? Well, you will have to chop off one of the arms of a geologist to get a clear answer on that, but there are usually several hundred to several thousand years between eruptions in this field. The last one was about 600 years ago, so it might be a while before it is “overdue”, but it might be soon as well.

El Nathan