Options
Németh, Károly
Loading...
12 results
Now showing 1 - 10 of 12
- PublicationRestrictedEmplacement conditions of the 1256 AD Al-Madinah lava flow field in Harrat Rahat, Kingdom of Saudi Arabia - Insights from surface morphology and lava flow simulations(2016)
; ; ; ; ; ; ; ; ; ; ; ;; ;; ; ;Lava flow hazard modelling requires detailed geological mapping, and a good understanding of emplacement settings and the processes involved in the formation of lava flows. Harrat Rahat, Kingdom of Saudi Arabia, is a large volcanic field, comprising about 1000 predominantly small-volume volcanoes most of which have emitted lava flows of various lengths. A few eruptions took place in this area during the Holocene, and they were located in the northern extreme of the Harrat Rahat, a close proximity to critical infrastructure and population living in Al-Madinah City. In the present study, we combined field work, high resolution digital topography and morphometric analysis to infer the emplacement history of the last historical event in the region represented by the 1256 AD Al-Madinah lava flow field. These datawere also used to simulate 1256 AD-type lava flows in the Harrat Rahat by theMAGFLOWlava flowemplacementmodel,which is able to relate the flowevolution to eruption conditions. The 1256 AD lava flow field extent was mapped at a scale of 1:1000 from a high resolution (0.5 m) Light Detection And Ranging (LiDAR) Digital TerrainModel (DTM), aerial photoswith field support. The bulk volume of the lava flow field was estimated at 0.4 km3, while the source volume represented by seven scoria cone was estimated at 0.023 km3. The lava flow covered an area of 60 km2 and reached a maximum length of 23.4 km. The lava flow field comprises about 20.9% of pāhoehoe, 73.8% of 'a'ā, and 5.3% of late-stage outbreaks. Our field observation, also suggests that the lava flows of the Harrat Rahat region are mainly core-dominated and that they formed large lava flow fields by amalgamation of many single channels. These channels mitigated downslope by topography-lava flow and channel–channel interactions, highlighting this typical process that needs to be considered in the volcanic hazard assessment in the region. A series of numerical lava flow simulations was carried out using a range of water content (0.1–1wt.%), solidification temperature (800–600 °C) and effusion curves (simple and complex curves). These simulations revealed that theMAGFLOW code is sensitive to the changes of water content of the erupting lava magma,while it is less sensitive to solidification temperature and the changes of the shape of effusion curve. The advance rate of the simulated lava flows changed from0.01 to 0.22km/h. Using data and observations from the youngest volcanic event of the Harrat Rahat as input parameters to MAGFLOW code, it is possible to provide quantitative limits on this type of hazard.145 5 - PublicationOpen AccessIncrement in the volcanic unrest and number of eruptions after the 2012 large earthquakes sequence in Central America(2021-11-17)
; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ;; ; ; ; ; ; ; ;Understanding the relationship cause/effect between tectonic earthquakes and volcanic eruptions is a striking topic in Earth Sciences. Volcanoes erupt with variable reaction times as a consequence of the impact of seismic waves (i.e. dynamic stress) and changes in the stress field (i.e. static stress). In 2012, three large (Mw ≥ 7.3) subduction earthquakes struck Central America within a period of 10 weeks; subsequently, some volcanoes in the region erupted a few days after, while others took months or even years to erupt. Here, we show that these three earthquakes contributed to the increase in the number of volcanic eruptions during the 7 years that followed these seismic events. We found that only those volcanoes that were already in a critical state of unrest eventually erupted, which indicates that the earthquakes only prompted the eruptions. Therefore, we recommend the permanent monitoring of active volcanoes to reveal which are more susceptible to culminate into eruption in the aftermath of the next large-magnitude earthquake hits a region.165 8 - PublicationOpen AccessTectonically-determined distribution of monogenetic volcanoes in a compressive tectonic regime: An example from the Pannonian continental back-arc system (Central Europe)This paper presents the results from a geographic information systems (GIS) workflow, which was used to analyze the spatial distribution and temporal evolution of volcanoes in the Mio-Pleistocene monogenetic Bakony- Balaton Highland Volcanic Field (BBHVF), located in the Pannonian Basin, Hungary. Volcanism occurred during the tectonic inversion in a back-arc setting and a compressive/transpressive tectonic regime on the hottest and thinnest lithosphere of continental Europe. The main goal of this study is to clarify the effect of the pre-existing structure of the upper lithosphere in the distribution of the volcanic centers across the volcanic field using an innovative GIS methodology. Orientation of the volcanic field was compared to the orientation of the faults in the BBHVF, and in its larger vicinity, which resulted in correspondence, suggesting the dominance of the SW-NE direction. The directions of the volcanic lineaments fit well to the two main fault directions. The fault-volcano proximity analysis suggests that the fault plane of a thrust fault was an important structural feature during the lifespan of the volcanism. All results suggest that the fault plane of a regionally significant Cretaceous thrust fault (Lit ́er Fault) might have served as a temporary pathway for the ascending magma, whereby (similarly to other, smaller faults) redirecting the magmas causing clustering of the volcanoes. This highlights the importance of major upper crustal structural heterogeneities for magma transport in a compressive tectonic system, espe- cially in the case of active, monogenetic volcanic fields from a volcanic hazard perspective. The present GIS workflow can be effective in analyzing the spatial patterns of the volcanism and its connection with crustal structures at monogenetic volcanic fields worldwide.
37 8 - PublicationOpen AccessMio/Pliocene phreatomagmatic volcanism in the Western Pannonian Basin(2004-08-01)
; ; ;Martin, U.; KTB ;Nemeth, K.; Massey University; 363 931 - PublicationOpen AccessRemnants of a Young Monogenetic Volcanic Field and the Fragile Balance of Anthropogenic InteractionThe rapid development of Auckland City in New Zealand from an initial rural settlement to a global urban hub produced a characteristic footprint on the Auckland Volcanic Field (AVF). This process was facilitated by increased anthropogenic activity that has resulted in the deterioration and destruction of many volcanic landforms and caused severe archaeological, cultural, geological and educational losses in an alarmingly short timescale. The AVF has 53 volcanic centres, and of these, 17% are classified as intact, 28% are partially intact, 30% are partially destroyed, and 25% are destroyed (including 13% that have no trace left). Based on surface area, approximately 40% of volcanic deposits in the AVF have been lost. The most common causes for impacts are public land use, quarrying and urban development. Regardless, there is significant potential to be found in the balance between the losses and gains of anthropogenic impacts on volcanic landforms. In the AVF and worldwide, geological studies have often been assisted by the presence of outcrops created by quarrying, mining, transport infrastructure and other modifications of volcanic landforms. Areas of significant volcanic geoheritage worldwide are often linked with these impacted volcanoes, and the information gained from these geoheritage areas assists in the management of geodiversity and geoeducation. Several volcanic centres are currently at risk of further destruction in the near future (Crater Hill, Waitomokia, Maugataketake, Kohuroa, Three Kings, St Heliers and McLaughlins Mt) and should be prioritised for any possible research before it is too late. We propose that a geological assessment should be a requirement before and, if possible, during any land development on or near a volcanic landform. Allowing access to scientists through the course of development in areas with volcanic landforms would, in turn, aid public and governing bodies in decision-making for the future of the city and its volcanoes in terms of increased knowledge of volcanic mechanisms of the AVF and awareness of the potential associated hazards.
30 5 - PublicationOpen Access
1164 19645 - PublicationOpen AccessLava Flow Hazard and Its Implication in Geopark Development for the Active Harrat Khaybar Intracontinental Monogenetic Volcanic Field, Saudi ArabiaHarrat Khaybar is an active monogenetic volcanic field in western Saudi Arabia that hosts spectacular monogenetic volcanoes and a Holocene volcanic cone with extensive lava fields. The volcanic region is a subject of intensive land use development, especially along tourism ventures, where the volcanic features are the key elements to utilize for increasing visitation rates to the region. The youngest eruption is suspected to be Holocene and occurred fewer than 5000 years ago based on the cross-cutting relationship between the youngest lava flows and archaeological sites. Lava flows are typical, from p¯ahoehoe to ‘a‘¯a types with great diversity of transitional textural forms. Here, we recorded typical transitional lava flow surface textures from the youngest flows identified by digital-elevation-model-based terrain analysis, satellite imagery, and direct field observations. We performed lava flow simulations using the Q-LavHA plug-in within the QGIS environment. Lava flow simulations yielded satisfactory results if we applied eruptions along fissures, long simulation distances, and ~5 m lava flow thickness. In these simulations, the upper flow regimes were reconstructed well, but long individual lava flows were not possible to simulate, suggesting that morphological steps likely promoted lava ponding, inflation, and sudden deflation by releasing melts further along shallow syneruptive valley networks.
26 20 - PublicationRestrictedGeosite determination based on geodiversity assessment utilizing the volcanic history of a near-sea-level explosive eruption-dominated volcanic island: Tūhua/Mayor Island, New Zealand(Geological Society of London, 2022)
; ; ; ; ; ; ;Tūhua/Mayor Island is located approximately 45 km off the NE coast of the North Island of New Zealand. This island was formed by various explosive and effusive volcanic eruptions commonly influenced by magma–water interaction eruption events occurring since the Pleistocene. The wider area of theSWPacific contains numerous volcanic islands with a similar type of volcanic evolution. Tūhua/Mayor Island should be studied in more detail to understand the underlying volcanic mechanisms and apply this research to other volcanic islands in the SW Pacific. Mayor Island, also known by its indigenous Māori name Tūhua (obsidian in Māori), provides an ideal site for studying current volcanism. The present day island was formed around 150 ka ago and contains several rhyolitic lava-flows from different time periods, pyroclastic-flow deposits generated by small volume localized eruptions and ignimbrite deposited by large explosive eruptions. Our research utilized a qualitative–quantitative assessment of geodiversity estimates to highlight possible geosites for the collection of precise information about the geological evolution of this area, demonstrating the potential of geoeducational sites. The term geodiversity recognizes geological and geomorphological elements, which have shaped the Earth’s surface and underly our abiotic environment. Additionally, volcanic heritage was included in our equation, specifically tailored for Tūhua/Mayor Island and based on expert views (qualitative model). This model allows for a wider diversity for the area of research compared with the original method, which utilized only geological elements. The results show that areas with pyroclastic deposits exposed on the cliffs and in the centre of the collapse caldera should be considered for the further study for geosite planning.27 1 - PublicationRestrictedVolcanic Lakes(2015-03)
; ; ; ; ; ; ; ; ; ; ; Volcanic lakes are amongst the most spectacular natural features on the planet. These intersections of magmatic-hydrothermal systems and the Earth’s surface are, poetically speaking, “blue windows” into the depth of a volcano (Fig. 1). The changing water compositions and colors of these lakes over time provide insights into the volcanic, hydrothermal and degassing processes of the underlying volcano.62 7 - PublicationOpen AccessThe Vanishing Volcanic Geoheritage of a Key Scoria Cone and its Significance in Volcanic Hazard Resilience of the Active Monogenetic Volcanic Field near Al Madinah, Kingdom of Saudi Arabia(2023)
; ; ; ; ; ; ; ; ; ; ; ; ; Four small scoria cones in the western outskirts of Al Madinah City, the Kingdom of Saudi Arabia, form a distinct young volcanic landmark. These volcanoes, despite their very small size, provide one of the most fundamental sources of information about the early eruption mechanism of rising mafic magma in the context of an active volcanic field located next to a city with over one million people. An initial study of the area in 2012–2013 confirmed that these sites had a significant phreatomagmatic phase in their opening stage, leaving behind characteristic pyroclastic successions likely to be covered by subsequent eruptive products. The fact that in this location, unequivocal evidence emerged to show that explosive magma-water interaction driven eruptions occurred in the largely magmatic (“dry”) explosive style, and volcanic field evolution confirmed that this site has high geoheritage value. Since the first research was 20 years ago, a restudy of the present-day condition of the scoria cone was conducted. Applying satellite imagery, remote sensing and direct site visit, we find that about a third of the cone surface area has been modified and at least a quarter of its volume has vanished. Further excavation for cone material however opened the entire western side of the cone, exposing a nearly 5-m-thick succession of accidental lithic pyroclast-dominated lapilli tuff and tuff breccia, confirming that this location had a significant phreatomagmatic phase in its opening eruptions. This location shows graphically the need for geoconservation to preserve such sites that are potentially the only, or best locations to show the potential eruptive styles and scenarios of future eruptions if they occur in similar environments.38 17