Volcanoes in Poland? It is difficult to believe, but…
Not so long ago (of course, in the “geological” sense of time), the territory of the current Inner Carpathians, i.e. south of the Pieniny Mountains and of the Outer Carpathians (the area of the present-day Beskidy Mountains) was covered by the sea, on the bottom of which large-scale tectonic processes were occurring in relation with pressing of the African continent onto the European platform. As a result of enormous stresses, the Earth’s crust was cracking, allowing molten magma to come out on the surface.
Most people with the term “volcanism” associate only volcanic cones of Italy, such as Stromboli, Mount Etna or Mount Vesuvius or volcanic fissures of Iceland (memorable eruption of the Eyjafjallajökull volcano in 2010 paralysed virtually the entire air traffic). In geology, the term of volcanism is much broader and is understood as the whole of phenomena related with magma’s coming out on the surface – this term also includes gas exhalations, eruptions of volcanic dusts, etc. However, many processes involving the movement of magma occur under the surface of the Earth and sometimes only from indirect indications we may conclude what happens undeground. Such phenomena are called plutonism. Volcanism and plutonism are referred to as magmatism. During both plutonic and volcanic processes rocks are formed, which provide an enormous amount of information.
For example, thin layers of volcanic dusts may be used for dating modern sediments – the method similar to the age determination on the basis of tree rings (dendrochronology) or lake varves (varve chronology). In flysch sediments of the Carpathians and the Foredeep there are, in turn, three layers of tuffites constituting correlation levels. On the basis of the composition of igneous rocks, we can determine the chemical composition of the mantle, i.e. the zone located between the core and the crust. So called xenoliths are helpful here. What is more, the chemical composition of igneous rocks is closely associated with their genesis. On this basis, geologists are able to determine, for example, whether a given rock has been formed in the rift zone (this may be evidenced by basalts of oceanic rifts with a specific chemical composition, the so-called MORBs – mid ocean ridge basalts) or subduction.
Igneous rocks originating from solidified lava or magma are not the only products of magmatism. Hot magma changes its surroundings through sintering of surrounding rocks, replacement of chemical components and cracking of surrounding rocks. The effects may also be a so called contact aureole i.e. the zone on the border of the magma body built of rocks, altered by the impact of magma, the formation of deposits and accumulations of minerals, the formation of hot springs or mineral waters. Most of the above elements may be found in the Polish Carpathians on the border between the Pieniny Mountains, Gorce Mountains and Beskid Sądecki. In this area, there are numerous andesite intrusions whose genesis is probably related to the subduction zone.