As we move inexorably towards the end of yet another year, it is inevitable that we think back on what the old year has brought. One of my favourite memories of 2015 is the visit we; Carl, Shérine and myself, paid to a couple of volcanic monuments in southern Sweden; Rallate and Jällabjär, at the end of April. In spite of Volcanocafé usually dealing in “big” volcanoes and eruptions, this week’s article will deal something very small, inconspicuous and ancient. Most of us do not live close to something big, imposing and recent, yet anything volcanic can be of interest and immensely satisfying seen close up and first hand.
With the break-up of the super-continent Pangea, the southern region of Fennoscandia (Scandinavia, Finland and the Kola peninsula) was subjected to stresses and about 190 MY BP it began to crack along a line known as the Tornquist Zone, named after the German geologist Alexander Tornquist. This was on or near the border between the igneous bedrock of the Baltic Shield and the mainly sedimentary continent of Avalonia as they collided. For a period of approximately 100 million years, the Tornquist line was volcanically active and at the time when the basalt pile at Rallate was formed, 110 MY BP, there were approximately some 150 volcanoes along the Tornquist zone.
Located a very convenient 20 m from a main road with a parking zone a mere 150 m away, the small pile of columnar basalt at Rallate is easily accessible. It was formed 110 MY BP when magma solidified inside the volcanic plumbing and as it cooled, it shrunk to form the six-sided columns typical of basalt. As these columns tend to align perpendicular to the front of cooling, their orientation, roughly at 30 degrees from the horizontal, indicate that this may have been a side vent of a larger volcano. In spite of numerous periods of glaciation, the small basalt pile at Rallate has survived because of the hardness of basalt and its high degree of resistance to erosion.
Another interesting observation was that the usually white Wood Anemones (Anemone nemorosa) were discoloured, a violetish purple, in certain areas. This is indicative of copper being present in the soil, so in spite of not bringing along a complete laboratory, we were able to say something of the mineral composition of the basalt. In bygone days, discoloration of flowers was a very important diagnostic tool of mineral prospectors, so in that sense we were also walking in the footsteps of ancient miners.
The weather being typical of what we in Sweden term “April weather”; rainfall intermingled with snow, we had to seek shelter at Skäralid National Park where they serve excellent coffee and an apple pie with custard well worth a visit if you should find yourself in the vicinity. (Nota bene: The small museum co-located with the restaurant and tourist office however, is not worth a visit.)
Once the weather had cleared sufficiently, we set out for Jällabjär, a volcano proper located about three or four miles away from Skäralid that rises some 60 metres above the surrounding landscape. Although its shape resembles that of a volcano, it is in fact the result of glacial erosion. After trekking an exploratory 200 metres, Carl and myself being better albeit still insufficiently shod as well as being the gentlemen we are, began to debate if proceeding was not best deferred when to our surprise Shérine took the lead and maintained it to the very summit, something that left Carl and myself slightly, erm…, winded.
As we progressed, we noted the signs of the boar infestation currently plaguing Southern Sweden even if the boars themselves kept out of view. From old constructions such as small bridges over brooks and agricultural enclosing walls, it was easy to see that this was indeed volcanic land as igneous rocks, predominantly basalt were omnipresent. Some were more interesting than others as they showed unmistakable grains of the minerals pyrite and chalcopyrite whereas even more interesting were the few ones with well-separated feldspar and quartz in direct contact with basalt. By now, unfortunately none of the photographic appliances brought along specifically for such an occasion (i.e. cell phones) were working which was a shame especially since some of the views were stunning.
So, does it have to be big in order to be of interest? My own answer to the question initially posed is no, it does not! I am certain that quite close to where you live, there is something volcanic of interest, so why not meet up with a couple of friends and go for an excursion! At the very least you ought to have a nice outing and, with a slice of luck, be able find a place that serves a decent coffee plus pie and custard.