23 research outputs found
Basaltic Dyke with Specific Volcanogenic Structures and its geomorphic evolution: Unique Geoheritage of the Faroe Islands (North Atlantic Ocean)
Volcanic landforms resulting from Cenozoic volcanism represent the most peculiar features of global geodiversity and provide eminent narratives for geoeducation. Among them, however, relict volcanic forms and site-specific landforms in remote areas have received less attention. In this paper, we provide the first description of unique volcanogenic features (hereinafter referred to as pseudo-hieroglyphs) developed on a summit rock wall at the Sandfelli ridge near the village of GjĂłgv in the N Eysturoy Island (Faroe Islands). The geomorphic evolution of the ridge and rock wall during the Quaternary is described and detailed petrographic analyses of the volcanogenic features are provided. Based on observed petrographical features, we interpret the pseudo-hieroglyphs to probably represent unique examples of chaotic horizontal columnar jointing. Following the geomorphological and petrographic examination of the study site, we analyse current Faroese legislation aiming at nature conservation and use this case to discuss broader implications of geoheritage conservation and geotourism in distant regions.Vulkanická krajina vzniklá kenozoickĂ˝m vulkanismem pĹ™edstavuje nejpodivnÄ›jšà rysy globálnĂ geodiversity a poskytuje vynikajĂcĂ pĹ™ĂbÄ›hy pro geovzdÄ›lávánĂ. MĂ©nÄ› pozornosti se však dostává reliktnĂm vulkanickĂ˝m formám a lokálnĂm tvarĹŻm reliĂ©fu v odlehlĂ˝ch oblastech. V tomto ÄŤlánku pĹ™inášĂme prvnĂ popis unikátnĂch vulkanogennĂch tvarĹŻ (dále jen "pseudo-hieroglyfy"), kterĂ© se vyvĂjely na skalnĂ stÄ›nÄ› vrcholu na hĹ™betÄ› Sandfelli u vesnice GjĂłgv v severnà části ostrova Eysturoy (FaerskĂ© ostrovy). Je popsán geomorfologickĂ˝ vĂ˝voj hĹ™betu a skalnĂ stÄ›ny bÄ›hem kvartĂ©ru a jsou uvedeny podrobnĂ© petrografickĂ© analĂ˝zy vulkanogennĂch vlastnostĂ. Na základÄ› pozorovanĂ˝ch petrografickĂ˝ch rysĹŻ interpretujeme pseudo-hieroglyfy, kterĂ© pravdÄ›podobnÄ› pĹ™edstavujĂ jedineÄŤnĂ© pĹ™Ăklady chaotickĂ© horizontálnĂ sloupcovitĂ© odluÄŤnosti. Po geomorfologickĂ©m a petrografickĂ©m studiu zájmovĂ© lokality analyzujeme souÄŤasnou faerskou legislativu zaměřenou na ochranu pĹ™Ărody a uĹľĂváme tohoto pĹ™Ăkladu k diskusi širšĂch dĹŻsledkĹŻ zachovánĂ a geoturistiky geografickĂ©ho dÄ›dictvĂ ve vzdálenĂ˝ch regionech
Sensitivity to Volcanic Field Boundary
Volcanic hazard analyses are desirable where there is potential for future volcanic activity to affect a proximal population. This is frequently the case for volcanic fields (regions of distributed volcanism) where low eruption rates, fertile soil, and attractive landscapes draw populations to live close by. Forecasting future activity in volcanic fields almost invariably uses spatial or spatio-temporal point processes with model selection and development based on exploratory analyses of previous eruption data. For identifiability reasons, spatio-temporal processes, and practically also spatial processes, the definition of a spatial region is required to which volcanism is confined. However, due to the complex and predominantly unknown sub-surface processes driving volcanic eruptions, definition of a region based solely on geological information is currently impossible. Thus, the current approach is to fit a shape to the known previous eruption sites. The class of boundary shape is an unavoidable subjective decision taken by the forecaster that is often overlooked during subsequent analysis of results. This study shows the substantial effect that this choice may have on even the simplest exploratory methods for hazard forecasting, illustrated using four commonly used exploratory statistical methods and two very different regions: the Auckland Volcanic Field, New Zealand, and Harrat Rahat, Kingdom of Saudi Arabia. For Harrat Rahat, sensitivity of results to boundary definition is substantial. For the Auckland Volcanic Field, the range of options resulted in similar shapes, nevertheless, some of the statistical tests still showed substantial variation in results. This work highlights the fact that when carrying out any hazard analysis on volcanic fields, it is vital to specify how the volcanic field boundary has been defined, assess the sensitivity of boundary choice, and to carry these assumptions and related uncertainties through to estimates of future activity and hazard analyses