Papers by Gabor Kereszturi
International Journal of Applied Earth Observation and Geoinformation, 2018
Optical and laser remote sensing provide resources for monitoring volcanic activity and surface h... more Optical and laser remote sensing provide resources for monitoring volcanic activity and surface hydrothermal alteration. In particular, multispectral and hyperspectral imaging can be used for detecting lithologies and mineral alterations on the surface of actively degassing volcanoes. This paper proposes a novel workflow to integrate existing optical and laser remote sensing data for geological mapping after the 2012 Te Maari eruptions (Tongariro Volcanic Complex, New Zealand). The image classification is based on layer-stacking of image features (optical and textural) generated from high-resolution airborne hyperspectral imagery, Light Detection and Ranging data (LiDAR) derived terrain models, and aerial photography. The images were classified using a Random Forest algorithm where input images were added from multiple sensors. Maximum image classification accuracy (overall accuracy = 85%) was achieved by adding textural information (e.g. mean, homogeneity and entropy) to the hyperspectral and LiDAR data. This workflow returned a total surface alteration area of ~0.4 km 2 at Te Maari, which was confirmed by field work, lab-spectroscopy and backscatter electron imaging. Hydrothermal alteration on volcanoes forms precipitation crusts on the surface that can mislead image classification. Therefore, we also applied spectral matching algorithms to discriminate between fresh, crust altered, and completely altered volcanic rocks. This workflow confidently recognized areas with only surface alteration, establishing a new tool for mapping structurally controlled hydrothermal alteration, evolving debris flow and hydrothermal eruption hazards. We show that data fusion of remotely sensed data can be automated to map volcanoes and significantly benefit the understanding of volcanic processes and their hazards. 2
Geology, 2017
Spatial forecasting of volcanism and associated hazards in intraplate monogenetic volcanic fields... more Spatial forecasting of volcanism and associated hazards in intraplate monogenetic volcanic fields is subject to large uncertainties in both data and models. We demonstrate a novel logistic regression method for mapping phreatomagmatic-magmatic eruption transition susceptibility using near-surface hydrologic, topographic and geological data. The method is illustrated on the Auckland Volcanic Field (AVF), New Zealand, which hosts New Zealand largest city, Auckland. Environmental factors examined for possible influence included the thickness of water-saturated and porous sediments, substrate-type and geology, vent elevation, and distance from the nearest fault. By comparing these factors with the volumes and styles of past eruption sequences, a location-specific eruption sequence forecasting model was constructed, recognizing that larger/longer eruptions are more likely to exhaust vent-area sources of water. Estimating volcanic hazard susceptibility in this way allows more effective planning and improved pre-eruption preparedness between eruptions and during future volcanic crises.
New Zealand Journal of Geology and Geophysics, 2016
Remotely sensed topographic datasets are a major source of information in modelling environmental... more Remotely sensed topographic datasets are a major source of information in modelling environmental and geomorphic processes. In this investigation, four of the most popular remotely sensed topographic datasets, available for the Auckland Volcanic Field (AVF; New Zealand), were compared using high-accuracy control points, such as Real-Time-Kinematic Global Positioning System (RTK GPS) profiles, as well as a Terrestrial Laser Scanning (TLS) surface. The LiDAR data were found to be most accurate with a Root Mean Squares Error (RMSE) of ±0.9 m, while other datasets such as contour-derived DEM, SRTM DTM and ASTER GDEM were found to be accurate at 5-10 m levels. As part of the error assessment, an extensive comparison was carried out between a range of popular terrain attributes (e.g. elevation, volume and slope angle) to determine their variability as a function of input data properties (e.g. surveying technique and data structure). This study shows that the eruptive volumes of monogenetic volcanoes are sensitive to the input data type and its spatial resolution. The moderately vegetated lava flow fields of Rangitoto have an uncertainty in eruptive volume estimate by ±15% due to the overall surface roughness. For hazard assessment purposes in the AVF, resampled LiDAR datasets are reliable; however, other datasets, such as contour-derived DEM and SRTM DTM, can be used to estimate eruptive volumes of monogenetic volcanoes.
Geomorphology, 2016
Conical volcanic edifices that are made up from lapilli to block/bomb pyroclastic successions, su... more Conical volcanic edifices that are made up from lapilli to block/bomb pyroclastic successions, such as scoria cones, are widespread in terrestrial and extraterrestrial settings. Eruptive processes responsible for establishing the final facies architecture of a scoria cone are not well linked to numerical simulations of their post-eruptive sediment transport. Using sedimentological, geomorphic and 2D fragment morphology data from a 15-ky-old scoria cone from the Cima Volcanic Field, California, this study provides field evidence of the various post-eruptive sediment transport and degradation processes of scoria cones located in arid to semi-arid environments. This study has revealed that pyroclast morphologies vary downslope due to syn-eruptive granular flows, along with post-eruptive modification by rolling, bouncing and sliding of individual particles down a slope, and overland flow processes. The variability of sediment transport rates on hillslopes are not directly controlled by local slope angle variability and the flank length but rather by grain size, and morphological characteristics of particles, such as shape irregularity of pyroclast fragments and block/lapilli ratio. Due to the abundance of hillslopes degrading in unvegetated regions, such as those found in the Southwestern USA, granulometric influences should be accounted for in the formulation of sediment transport laws for geomorphic modification of volcanic terrains over long geologic time.
Conical volcanic edifices that are made up from lapilli to block/bomb pyroclastic successions, su... more Conical volcanic edifices that are made up from lapilli to block/bomb pyroclastic successions, such as scoria cones, are widespread in terrestrial and extraterrestrial settings. Eruptive processes responsible for establishing the final facies architecture of a scoria cone are not well linked to numerical simulations of their post-eruptive sediment transport. Using sedimentological, geomorphic and 2D fragment morphology data from a 15-ky-old scoria cone from the Cima Volcanic Field, California, this study provides field evidence of the various post-eruptive sediment transport and degradation processes of scoria cones located in arid to semi-arid environments. This study has revealed that pyroclast morphologies vary downslope due to syn-eruptive granular flows, along with post-eruptive modification by rolling, bouncing and sliding of individual particles down a slope, and overland flow processes. The variability of sediment transport rates on hillslopes are not directly controlled by local slope angle variability and the flank length but rather by grain size, and morphological characteristics of particles, such as shape irregularity of pyroclast fragments and block/lapilli ratio. Due to the abundance of hillslopes degrading in unvegetated regions, such as those found in the Southwestern USA, granulometric influences should be accounted for in the formulation of sediment transport laws for geomorphic modification of volcanic terrains over long geologic time. Figure 1: (A) Location of the Cima Volcanic Field in California. (B) Orthophoto of the Black Tank cone with the major geomorphic features (dashed black line), such as crater, flank, debris apron and distal tephra blanket, as well as the numbered sampling locations. (C) Details of the analyzed profiles through the volcanic edifice. Lines with F1-F51 are the radial profiles on the flank (white lines) and the apron (white dashed lines). R1-R2 is the profile along the crater rim. The white triangle is the mean center of the crater.
Updates in Volcanology - New Advances in Understanding Volcanic Systems, 2012
The weak geophysical precursors of the 6 August 2012 Te Maari eruption of Mt. Tongariro and a lac... more The weak geophysical precursors of the 6 August 2012 Te Maari eruption of Mt. Tongariro and a lack of obvious juvenile components in its proximal ballistic deposits imply that the eruption was caused by the sudden decompression of a sealed, hot hydrothermal system. Strong magmatic signals in pre-and post-eruption gas emissions indicate that fresh magma had intruded to shallow levels shortly before this eruption. Here we examine the volcanic ash produced during the August eruption with the aim of determining whether juvenile magma was erupted or not. The widely applied criteria for identifying fresh juvenile pyroclasts provided inconclusive results. The Te Maari ash sorting and trend towards a unimodal grain-size distribution increase with distance along the dispersal axis. Proximal to intermediate sites showing polymodal grain-size distributions can be related to the refragmentation of different pre-existing lithologies, overlapped erupted pulses and transport mechanisms, and to particle aggregation. Between 69 and 100 vol.% of particles coarser than 3 ϕ and 45-75 vol.% of grains finer than 3 ϕ were sourced from the pre-existing, commonly hydrothermally altered, vent-area lavas and pyroclasts. Free crystals (pyroxene N plagioclase N magnetite N pyrite) make up 0-23 vol.% of particles coarser than 3 ϕ, and 22-41 vol.% of grains finer than 3 ϕ. Brown to black fragments of fresh glass are a small (1-15 vol.%), but notable, component. Under SEM, these blocky, glassy particles are poorly vesicular, and irregularly shaped, some with fluidal or bubble-wall surfaces, and others with fragmented stepped surfaces and fine adhering ash. In thin section, they contain variable amounts of microlites within an isotropic groundmass. The range in silica content of the microprobe-analysed glass is very wide (56-77 wt.%) and cannot be correlated to any specific particle textural type. These chemically and texturally diverse glassy fragments are identical to mechanically broken pieces of country rock lavas and pyroclasts; both their diversity, and their match with vent country rocks, argue strongly against a "juvenile" origin for the glassy fragments. We conclude that rising magma provided only heat and gas into the overlying, sealed vapour-dominated hydrothermal system. A landslide from this area led to a rapid decompression and ash was produced by top-down hydrothermal explosions. Careful attention must be paid to the combination of compositions and textures of fine ash particles in such situations, as well as to the context of their source vent, in order to be confident that new magma has reached the surface.
Bondoró Volcanic Complex (shortly Bondoró) is one of the most complex eruption centre of Bakony-B... more Bondoró Volcanic Complex (shortly Bondoró) is one of the most complex eruption centre of Bakony-Balaton Highland Volcanic Field, which made up from basaltic pyroclastics sequences, a capping confined lava field (∼4 km 2 ) and an additional scoria cone. Here we document and describe the main evolutional phases of the Bondoró on the basis of facies analysis, drill core descriptions and geomorphic studies and provide a general model for this complex monogenetic volcano. Based on the distinguished 13 individual volcanic facies, we infer that the eruption history of Bondoró contained several stages including initial phreatomagmatic eruptions, Strombolian-type scoria cones forming as well as effusive phases. The existing and newly obtained K-Ar radiometric data have confirmed that the entire formation of the Bondoró volcano finished at about 2.3 Ma ago, and the time of its onset cannot be older than 3.8 Ma. Still K-Ar ages on neighbouring formations (e.g. Kab-hegy, Agár-tető) do not exclude a long-lasting eruptive period with multiple eruptions and potential rejuvenation of volcanic activity in the same place indicating stable melt production beneath this location. The prolonged volcanic activity and the complex volcanic facies architecture of Bondoró suggest that this volcano is a polycyclic volcano, composed of at least two monogenetic volcanoes formed more or less in the same place, each erupted through distinct, but short lived eruption episodes. The total estimated eruption volume, the volcanic facies characteristics and geomorphology also suggests that Bondoró is rather a small-volume polycyclic basaltic volcano than a polygenetic one and can be interpreted as a nested monogenetic volcanic complex with multiple eruption episodes. It seems that Bondoró is rather a "rule" than an "exception" in regard of its polycyclic nature not only among the volcanoes of the Bakony-Balaton Highland Volcanic Field but also in the Neogene basaltic volcanoes of the Pannonian Basin.
Journal of Volcanology and Geothermal Research, 2011
The occurrence, shape, structure and eruption style of monogenetic volcanoes, such as maars, tuff... more The occurrence, shape, structure and eruption style of monogenetic volcanoes, such as maars, tuff rings, tuff cones and scoria cones, are generally governed by several internal (composition of the magma, magmatic flux, ascent rate, viscosity, volatile contents) and external conditions (regional and local tectonics, topography, and the presence of surfacial, ground and meteoric water). These controlling factors are together responsible for the eruption style, distribution pattern, volcanic facies architecture and morphology of the monogenetic volcanic landforms. The Late Miocene to Pleistocene Bakony-Balaton Highland Volcanic Field (BBHVF) in western Hungary is a typical small sized (b 50 eruption centres), basaltic, intraplate "monogenetic" volcanic field. Generally, initial eruptions of the BBHVF were phreatomagmatic (n =~28); however, a lesser number (n =~14) of predominantly scoria cone forming eruptions are also inferred. The temporal distribution of the Strombolian style scoria cones was concentrated mostly between 3 and 2.5 Ma. A detailed study of the changes in eruption styles recorded in the pyroclastic sequences suggested a change from a conventional phreatomagmatic to a magmatic fragmentation style during the activity of the volcanic field. A clear correlation has been identified between the long-term environmental changes of the region that resulted in a gradual shift from a more phreatomagmatic eruption style to a more magmatic eruption style. Detailed examination of the temporal distribution of K-Ar and Ar-Ar radiometric data, Digital Elevation Model and Dense Rock Equivalent-based volume calculations of eruptive products and origin of pyroclastic rocks (e.g. phreatomagmatic or magmatic) preserved in variously eroded monogenetic volcanoes were utilized to integrate available volcanological and climatological data to identify potential links between external and internal controlling parameters that responsible for long-term eruption style changes. At least 6 volcanic cycles have been identified by cluster analysis. Time gap between the cycles were vary from 1.66 up to 0.06 Ma, while the average eruption recurrence rate was~0.1078 Ma/event. The timevolume diagram of the volcanism of BBHVF have shown time-predictive behavior combined with low magma-flux (total preserved volume~2.867 km 3 ) and output rates (0.53 km 3 /Ma for the entire volcanic field and 0.90 km 3 /Ma for the last 5 cycles), suggesting that volcanism was largely tectonically-controlled and not magmatically-controlled. Furthermore, the topographic differences between the northern ("elevated") and southern ("basin-like") parts of the volcanic field, are also important in local differences in dominant fragmentation style, because the elevated part of the field was prone to host large, more magmatically-evolved volcanoes, than on the lower, water-saturated, unconsolidated sediments, which favored to the magma/water interaction driven phreatomagmatic fragmentation. The third controlling parameter, which seems to play an important role in controlling the eruptive style of monogenetic volcanism at BBHVF, was the paleoclimate fluctuation, especially during the time interval of 3.0 to 2.5 Ma. Thus, mainly the long-term environmental changes (e.g. aridification) have been response the shifting fragmentation style from phreatomagmatic to more magmatic ones.
Central European Journal of Geosciences, 2011
Payún Matru Volcanic Field is a Quaternary monogenetic volcanic field that hosts scoria cones wit... more Payún Matru Volcanic Field is a Quaternary monogenetic volcanic field that hosts scoria cones with perfect to breached morphologies. Los Morados complex is a group of at least four closely spaced scoria cones (Los Morados main cone and the older Cones A, B, and C). Los Morados main cone was formed by a long lived eruption of months to years. After an initial Hawaiian-style stage, the eruption changed to a normal Strombolian, conebuilding style, forming a cone over 150 metres high on a northward dipping (∼4˚) surface. An initial cone gradually grew until a lava flow breached the cone's base and rafted an estimated 10% of the total volume. A sudden sector collapse initiated a dramatic decompression in the upper part of the feeding conduit and triggered violent a Strombolian style eruptive stage. Subsequently, the eruption became more stable, and changed to a regular Strombolian style that partially rebuilt the cone. A likely increase in magma flux coupled with the gradual growth of a new cone caused another lava flow outbreak at the structurally weakened earlier breach site. For a second time, the unstable flank of the cone was rafted, triggering a second violent Strombolian eruptive stage which was followed by a Hawaiian style lava fountain stage. The lava fountaining was accompanied by a steady outpour of voluminous lava emission accompanied by constant rafting of the cone flank, preventing the healing of the cone. Santa Maria is another scoria cone built on a nearly flat pre-eruption surface. Despite this it went through similar stages as Los Morados main cone, but probably not in as dramatic a manner as Los Morados. In contrast to these examples of large breached cones, volumetrically smaller cones, associated to less extensive lava flows, were able to heal raft/collapse events, due to the smaller magma output and flux rates. Our evidence shows that scoria cone growth is a complex process, and is a consequence of the magma internal parameters (e.g. volatile content, magma flux, recharge, output volume) and external conditions such as inclination of the pre-eruptive surface where they grew and thus gravitational instability.
According to Wood's model, morphometric parameters such as slope angle can provide valuable infor... more According to Wood's model, morphometric parameters such as slope angle can provide valuable information about the age of conical volcanic edifices such as scoria cones assuming that their initial slopes range from 30°to 33°, measured manually on topographic maps, and assuming that their inner architectures are homogenous. This study examines the morphometric variability of nine young (a few thousand years old) small-volume scoria cones from Tenerife, Canary Islands, using high-resolution digital elevation models in order to assess their slope angle variability. Because of the young age and minimal development of gullies on the flanks, their morphometric variability can be interpreted as the result of syn-eruptive processes including: (1) pre-eruptive surface inclination, (2) vent migration and lava outflow with associated crater breaching and diversity of pyroclastic rocks accumulated in the flanks of these volcanic edifices. Results show that slope angles for flank sectors differ by up to 12°among the studied volcanoes, which formed over the same period of time; this range greatly exceeds the 2-3°indicated by Wood. The greater than expected original slope range suggests that use of morphometric data in terms of morphometry-based relative dating and detection of erosional processes and settings must be done with great care (or detailed knowledge about absolute ages and eruption history), especially in field-scale morphometric investigation.
Morphometry-based dating provides a first-order estimate of the temporal evolution of monogenetic... more Morphometry-based dating provides a first-order estimate of the temporal evolution of monogenetic volcanic edifices located within an intraplate monogenetic volcanic field or on the flanks of a polygenetic volcano. Two widely used morphometric parameters, namely cone height/width ratio (H max /W co ) and slope angle, were applied to extract chronological information and evaluate their accuracy for morphometry-based ordering. Based on these quantitative parameters extracted from contour-based Digital Elevation Models (DEMs), two event orders for the Bandas del Sur in Tenerife (Canary Islands) were constructed and compared with the existing K-Ar, paleomagnetic and stratigraphic data. The results obtained suggest that the commonly used H max /W co ratio is not reliable, leading to inappropriate temporal order estimates, while the slope angle gives slightly better results. The overall performance of such descriptive parameters was, however, generally poor (i.e. there is no strong correlation between morphometry and age). The geomorphic/morphometric mismatches could be the result of (1) the diversity of syn-eruptive processes (i.e. diverse initial morphologies causing geomorphic/morphometric variability),
Journal of Volcanology and Geothermal Research, 2014
The weak geophysical precursors of the 6 August 2012 Te Maari eruption of Mt. Tongariro and a lac... more The weak geophysical precursors of the 6 August 2012 Te Maari eruption of Mt. Tongariro and a lack of obvious juvenile components in its proximal ballistic deposits imply that the eruption was caused by the sudden decompression of a sealed, hot hydrothermal system. Strong magmatic signals in pre-and post-eruption gas emissions indicate that fresh magma had intruded to shallow levels shortly before this eruption. Here we examine the volcanic ash produced during the August eruption with the aim of determining whether juvenile magma was erupted or not. The widely applied criteria for identifying fresh juvenile pyroclasts provided inconclusive results. The Te Maari ash sorting and trend towards a unimodal grain-size distribution increase with distance along the dispersal axis. Proximal to intermediate sites showing polymodal grain-size distributions can be related to the refragmentation of different pre-existing lithologies, overlapped erupted pulses and transport mechanisms, and to particle aggregation. Between 69 and 100 vol.% of particles coarser than 3 ϕ and 45-75 vol.% of grains finer than 3 ϕ were sourced from the pre-existing, commonly hydrothermally altered, vent-area lavas and pyroclasts. Free crystals (pyroxene N plagioclase N magnetite N pyrite) make up 0-23 vol.% of particles coarser than 3 ϕ, and 22-41 vol.% of grains finer than 3 ϕ. Brown to black fragments of fresh glass are a small (1-15 vol.%), but notable, component. Under SEM, these blocky, glassy particles are poorly vesicular, and irregularly shaped, some with fluidal or bubble-wall surfaces, and others with fragmented stepped surfaces and fine adhering ash. In thin section, they contain variable amounts of microlites within an isotropic groundmass. The range in silica content of the microprobe-analysed glass is very wide (56-77 wt.%) and cannot be correlated to any specific particle textural type. These chemically and texturally diverse glassy fragments are identical to mechanically broken pieces of country rock lavas and pyroclasts; both their diversity, and their match with vent country rocks, argue strongly against a "juvenile" origin for the glassy fragments. We conclude that rising magma provided only heat and gas into the overlying, sealed vapour-dominated hydrothermal system. A landslide from this area led to a rapid decompression and ash was produced by top-down hydrothermal explosions. Careful attention must be paid to the combination of compositions and textures of fine ash particles in such situations, as well as to the context of their source vent, in order to be confident that new magma has reached the surface.
Bulletin of Volcanology, 2012
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Papers by Gabor Kereszturi