A Badacsony freatomagmás piroklasztit-sorozata: következtetések a monogenetikus bazaltvulkáni működés folyamataira és formáira

Abstract

In this paper the first quantitative description and volcanological interpretation is given of the Badacsony Hill, the latter being the most well-known butte of the Bakony-Balaton Highland Volcanic Field (BBHVF). The pyroclast/lithics ratio of the pyroclastics was investigated by using point-counting image analysis methodology on the surfaces of handcut specimens. The isometrical shape of different grains allowed the obtained 2D data to be converted to 3D volume data. By using this methodology it was possible to infer the relative depth of explosions with respect to the synvolcanic surface and the syneruptive morphology; moreover, the effusive and explosive phases of the volcanism could be identified.The results of point-counting image analysis and the position and extent of the phreatomagmatic sequence on the Badacsony Hill imply that the Badacsony volcano was a monogenetic (probably polycyclic) tuff ring or shallow maar volcano. Such volcanism is associated with the interaction of hot, molten material with groundwater, and this triggers shallow explosions. The low amount of accidental lithics within the deposits confirms the tuff ring scenario; however, such a low amount of accidental lithics could also be observed within deposits from shallow maars when these were formed on a soft, unconsolidated basement. Such an alternative model is envisaged for Badacsony.The development of the volcanism can be divided into explosive and effusive phases, based on the different composition and on the relative stratigraphic position of the respective phreatomagmatic sequences. Based on these results the present study proposes a volcanic evolution model. Given the scarcity of volcanological data on the Badacsony Hill, the results presented here could give a basis for further regional volcanological investigations.Keywords: Badacsony, Bakony-Balaton Highland Volcanic Field, image analysis, maar, monogenetic, phreatomagmatic eruption, tuff ring Összefoglalás A tanulmányban a Bakony-Balaton-felvidéki vulkáni terület (BBVT) legismertebb tanúhegyén, a Badacsonyon kibukkanó freatomagmás piroklasztit-összlet első kvantitatív leírását és vulkanológiai értelmezését mutatjuk be. A piroklasztitok juvenilis/litikus törmelékeinek arányát pontszámlálásos módszerrel vizsgáltuk vágott kézipéldány-fel színe -ken. A felület%-ban kapott eredményeket a kőzetminták teljes térfogatára vonatkozónak vettük. E módszer segít ségével meghatároztuk a freatomagmás robbanások relatív mélységét a szinvulkáni felszínhez képest, következ tetéseket vontunk le a lehetséges szineruptív vulkánmorfológiára, valamint a terepi megfigyelések és korábbi tanulmányok alapján rekonst ruáltuk a vulkán működésének teljes fejlődéstörténetét.A képelemzés során megállapítottuk a litikus elegyrészek minimális arányát. Ebből, valamint a piroklasztitok térbeli elter jedéséből és rétegtani helyzetéből valószínűsíthető, hogy a Badacsony egy monogenetikus (esetleg policiklikus) tufagyűrű vagy sekély maar vulkán volt, amelynek kialakulásában a víz-magma kölcsönhatás követke...

Dilemma of Geoconservation of Monogenetic Volcanic Sites under Fast Urbanization and Infrastructure Developments with Special Relevance to the Auckland Volcanic Field, New Zealand

“…Most of these volcanoes formed large phreatomagmatic edifices that were subsequently filled with various late magmatic infills like those in Auckland [49]. Hungarian locations are Plio-Pleistocene in age [67], in contrast to Auckland; hence, the volcanoes have been eroded back to their core of crater and upper conduit filling successions [68], with no preserved successions of former tuff ring or medial to distal parts of their original volcanic edifices preserved [69].…”

Phreatomagmatic vs magmatic eruptive styles in maar-diatremes: a case study at Twin Peaks, Hopi Buttes volcanic field, Navajo Nation, Arizona

“…Another possibility is that the eruptive regime progressively switches from phreatomagmatic to magmatic. If a late magmatic phase of the eruption lasts long enough, the syn-eruptive maar crater could be filled (or over-filled) by a scoria cone Vazquez 1998) or a lava lake (e.g., Martin and Németh 2002;Kereszturi and Németh 2011;Hencz et al 2017;Latutrie and Ross 2018;Tietz et al 2018), so that the final landform at the end of the eruption would not necessarily be a maar, even if there is a diatreme under it. Williams (1936) studied both the HBVF and the older Navajo volcanic field further north.…”