Vladislav Rapprich

Late Miocene volcanic activity in the České středohoří Mountains (Ohře/Eger Graben, northern Bohemia)

Late Miocene volcanic activity in the České středohoří Mountains (Ohře/Eger Graben, northern Bohemia) First occurrences of superficial bodies of Late Miocene volcanic activity were found in the western part of the České středohoří Volcanic Complex (CSVC) and extended our knowledge of its volcanostratigraphy. Their K-Ar ages (9.59, 9.61 and 11.36 Ma) correspond to the age of alkaline basaltic rocks of the youngest known Intrusive Suite of this area. Unlike the previously known subvolcanic bodies of this system, the newly observed bodies are represented by superficial products: two scoria cones with remnants of lava flows and one exclusive lava flow produced from a lava cone. The magmas forming all three occurrences are basanitic. Their primitive chemical composition Sr (0.70347-0.70361) and Nd (0.51279-0.51284) isotope ratios are similar to the products of the first and third volcanic formation of the CSVC. The proved existence of superficial products of the youngest volcanic formation, together with clear superposition relations to sedimentary formations and the chemical character of the youngest magmas in the central part of the Ohře (Eger) Graben support the stratigraphic scheme of volcanic activity in the České středohoří Mts. The eruptive style of the youngest formation volcanoes was purely magmatic (Strombolian) with no phreatic influence.

Slope Dependent Morphometric Analysis as a Tool Contributing to Reconstruction of Volcano Evolution

People have been fascinated by volcanoes since time immemorial. This is mainly due to the serious consequences that volcanic eruptions represent for human society. Volcanic activity develops in various ways. Therefore, evolutionary trends and the history of the volcanic system should be well understood when future hazards must be predicted and their impact on human society reduced. A volcanos history can be reconstructed from its deposits, their superposition and spatial relationships. Geological mapping is the crucial method for acquiring this information. Unfortunately, large areas in volcanic zones are inaccessible for research directly in the field. In these areas, the geological setting must be investigated by a combination of remote sensing methods and field observations from accessible outcrops. Surface methods such as remote sensing and morphological analysis provide fast and relatively cheap information, complementary to classical field geology for studying the subsurface geology. These methods can be beneficial, especially for areas with poor accessibility and/or dense vegetation cover. Volcanoes or volcanic complexes quite often represent such areas. Land forms are a result of geologic and geomorphologic processes that occur on the earth’s surface thus land forms are not chaotic, but have been structured by geologic and geomorphologic processes over time. The geomorphology of volcanic formations as a whole seems to be a reflection of the underlying geology with steep-sided land forms occurring at each of the “strong” rock units and long, with gentle slopes and topographic breaks found on „soft“ rocks. To support this theory, we employed and tested new methodology combining information arising from field surveys together with visual interpretation and statistical spatial analysis of morphometric slope-depending classes to define the spatial extent of various volcanic formations and to identify major tectonic phenomena from features derived from the geomorphology in more accurate way.

A Crucial Site in the Argument Between Neptunists and Plutonists: Reopening of the Historical Adit in the Komorní hůrka (Kammerbühl) Volcano After 180 Years

A small, inconspicuous scoria cone in western Bohemia, known as Komorní hůrka Hill, played a crucial role during the controversy between Plutonists and Neptunists over the origin of rocks in the first half of the nineteenth century. The year 2017 represents the 180th anniversary of one successful resolution of this debate: at the instigation of J.W. Goethe, adits were dug into this volcano to access its feeding system in order to observe whether volcanoes were fed by burning coal seams, or feeder dikes of magma. The adits into Komorní hůrka Hill were the first large earth-works with a solely scientific goal and with no commercial mining purposes. The basaltic feeder exposed in the adits decided definitively in favour of the Plutonists after decades of ongoing arguments with the Neptunists. Here, we summarize the overall history of this small volcano. A recently conducted ground geophysical survey confirmed the position of historical adits, marked on several archive sketches. The geophysical data, comprising ground magnetometry, electric resistivity tomography and refraction seismic profiles, also revealed the internal structure of the volcano, including the position of the feeder dike and the geometry of a lava flow emitted from the crater. With the position of these historical adits confirmed by geophysical survey, excavations can safely reopen these historical earth-works and provide access to a wider public. Komorní hůrka could then serve as an educational geosite to exhibit the structure of a small monogenetic volcano, as well as illustrating a stage in the history of Earth Sciences.