Dávid Karátson

Palaeolimnology of the last crater lake in the Eastern Carpathian Mountains: a multiproxy study of Holocene hydrological changes

A multi-proxy investigation (loss-on-ignition, major and trace elements, pollen, plant macrofossil and siliceous algae) was carried out on the sediment of a crater lake (Lake Saint Ana, 950xa0m a.s.l.) from the Eastern Carpathian Mountains. Diatom-based transfer functions were applied to estimate the lake’s trophic status and pH, while reconstruction of the water-depth changes was based on the plant macrofossil and diatom records. The lowest Holocene water depths were found between 9000 and 7400xa0calibrated BP years, when the crater was occupied by Sphagnum-bog. Significant increases in water depth were found from 5350(1), 3300(2) and 2700xa0calxa0yrxa0BP. Of these, the first two coincided with major terrestrial vegetation changes, namely (1) the establishment of Carpinusxa0betulus on the crater slope and (2) the replacement of the lakeshore Piceaxa0abies forest by Fagusxa0sylvatica. The chemical record indicated significant soil changes along with the canopy changes (from coniferous to deciduous) that led to increased in-lake productivity and pH. A further increase in water depth around 2700xa0calxa0yrxa0BP resulted in stable thermal stratification and hypolimnetic anoxia that via P-release further increased in-lake productivity and eventually led to phytoplankton blooms with large populations of Scenedesmus. High productivity was depressed by anthropogenic lakeshore forest clearances from ca. 1000xa0calxa0yrxa0BP that led to the re-establishment of P.xa0abies on the lakeshore and consequent acidification of the lake water. On the whole, these data suggest that Lake Saint Ana is a vulnerable ecosystem: in-lake productivity is higher under deciduous canopy and litter, and considerably repressed by coniferous canopy and litter. The lake today subsists in a managed environment that is far from its natural state. This would be a dense F.xa0sylvatica forest supplying more nutrients and keeping up a more productive in-lake flora and fauna.

Preferred Clast Orientation in Volcaniclastic Mass-Flow Deposits: Application of a New Photo-Statistical Method

A photo-statistical method has been developed to quantify the strength of directional clast fabric in various types of volcaniclastic mass-flow deposits. Fabric strength (R) is defined as the resultant vec- tor length of clast alignment computed from clast angles visible on a vertical outcrop face. R can be obtained from photographs of an ex- posure via image analysis and statistical assessment with regard to clast number and direction of exposure face vs. paleoflow. Relative to tra- ditional, manual field measurements, the photo-statistical method gives reproducible quantitative results that are independent of subjective clast selection. On average, one hundred and fifty clasts are the mini- mum number necessary to obtain reliable R values. For determining the strength of directional fabric, it is more accurate to measure ran- domly collected clasts than only the most elongated ones (normally the practice during manual measurements), because more elongated clasts display a stronger fabric. Clast size generally does not influence clast alignment. R values obtained from lower or upper portions of vertical exposure faces may show significant differences if pronounced imbri- cation is developed in the lower part of the beds passing upward to purely bed-parallel clast alignment. Bimodality caused by the coexis- tence of imbricated and bed-parallel clasts tends to reduce R values. The studied examples include (1) near-vent breccias, (2) block-and- ash flow deposits, and (3) mostly cohesive volcaniclastic debris-flow deposits from 49 selected exposures (24 in Hungary, 6 in France, 4 in Japan, 3 in New Zealand, 2 in Indonesia, and 1 in the U.S.A., Argen- tina, Chile, Turkey, and Romania, each). Near-vent breccias show a relatively weak fabric (R

Rates and factors of stratovolcano degradation in a continental climate: A complex morphometric analysis for nineteen Neogene/Quaternary crater remnants in the Carpathians

Abstract The systematic age progression of the Neogene/Quaternary volcanic chain in the Carpathians, manifested in progressively degraded stratovolcanoes from south to north, offers a great opportunity to calculate erosion rates and the factors that control degradation in a moderate continental climate. Using available and newly determined K Ar ages for the cessation of volcanism of nineteen stratocones, a great number of morphometric variables, including crater diameter and perimeter, intracraterial valley length, valley order and density, dip of internal and external crater rim, cone diameter, relative height/cone diameter, height above and distance from base level, etc., has been examined by regression and factor analyses. On the one hand, the erosion rates which are calculated from the regression equations of a given characteristic versus age seem to answer the question of to what extent the stratovolcanoes are degraded: numerical values of crater enlargement (109 m/Ma), internal valley growth (1.3 km/Ma), average cone lowering (31.5 m/Ma), etc., are given. Moreover, using multiple regression equations as “age equations”, the age of any volcano in the same climate can be estimated from the measured characteristics. On the other hand, there are morphometric characteristics (e.g., dip of crater rim, crater circularity, intracraterial valley density) which are not functions of time. Three major factors, i.e., the “time factor” (about 40%), the “size-depth” factor (about 24%), and the “erosional distance” factor (about 10%) account for about 75% of the stratovolcano characteristics variance, and two additional factors (eruption style-magma viscosity, and the central manifestation of volcanism) may be responsible for a further 13%.

Towards reconstruction of the lost Late Bronze Age intra-caldera island of Santorini, Greece

During the Late Bronze Age, the island of Santorini had a semi-closed caldera harbour inherited from the 22 ka Cape Riva Plinian eruption, and a central island referred to as ‘Pre-Kameni’ after the present-day Kameni Islands. Here, the size and age of the intracaldera island prior to the Late Bronze Age (Minoan) eruption are constrained using a photo-statistical method, complemented by granulometry and high-precision K-Ar dating. Furthermore, the topography of Late Bronze Age Santorini is reconstructed by creating a new digital elevation model (DEM). Pre-Kameni and other parts of Santorini were destroyed during the 3.6 ka Minoan eruption, and their fragments were incorporated as lithic clasts in the Minoan pyroclastic deposits. Photo-statistical analysis and granulometry of these lithics, differentiated by lithology, constrain the volume of Pre-Kameni to 2.2–2.5 km3. Applying the Cassignol-Gillot K-Ar dating technique to the most characteristic black glassy andesite lithics, we propose that the island started to grow at 20.2u2009±u20091.0 ka soon after the Cape Riva eruption. This implies a minimum long-term lava extrusion rate of ~0.13–0.14 km3/ky during the growth of Pre-Kameni.

Tom Pfeiffer and Ingrid Smet: Volcano Discoveries: A Photographic Journey Around the World

Everyonewho travels to or works at volcanoes is fascinated by the unbelievable colorful world of Earth’s volcanoes and volcanic landscapes. Everyone takes “his” or “her” photo on the volcano, which becomes “my volcano” in memory. Many people were there, but I was also there! Now, Tom Pfeiffer, volcano lover, volcanologist, tour guide, and photographer, brings the impressive volcanic scenes to a broad audience via hundreds of selected volcano photos from all over the world, in his and his partner Ingrid Smet’s Volcano Discoveries: A Photographic Journey Around the World (New Holland Publisher, 2015). As the main author puts it simply, “volcanoes are a rather easy subject”, and “volcano photography really is mostly about being at the right place at the right time”. In fact, Pfeiffer was there: he was visiting or climbing the most famous volcanoes of the world as many times as was necessary, in order to take unsurpassable photos of volcanic eruptions, related phenomena, or just simply amazing volcanic landscapes. Holding a PhD degree in volcanology, Pfeiffer considers himself an amateur photographer, but, obviously, the way he takes photos is greatly helped by his profession. He always looks at, and captures, what he needs to look at, and the result is a unique set of the thousand faces of Earth’s volcanoes. The writer of this review has also visited a number of the volcanoes on Pfeiffer’s photographs. After taking one’s own pictures, it is easy to think “though I am an amateur, my photo is really beautiful, is not it?” Whether or not Pfeiffer is an amateur, there is no question that his shots are difficult if not impossible to improve upon. Even the simplest stories, such as the well-known eruptions of Stromboli, tell something new, and basically every aspect that he captures adds to the common view of the target volcano. Not surprisingly, this year, for instance, two photos from Pfeiffer’s endless collection appeared in the 2017 IAVCEI calendar (and there could have been many more). As for his photography, the shots are rarely about effects or tricks, rather they deliver the personal feeling of being there. Most of them, as Pfeiffer explains, “were taken at fairly easily accessible volcanoes and under conditions that did not involve high risk”. However, it is easy to see that this could not have been so simple, and Pfeiffer always did his best to share his “being there” feeling: during the night, at peep of dawn, in the companion of local peasants, or among other volcano lovers admiring the landscape. Many photos on volcanoes and their Editorial responsibility: K. Németh

Evidence for post-depositional diffusional loss of hydrogen in quartz phenocryst fragments within ignimbrites

Abstract Ignimbrite-hosted quartz phenocryst fragments contain much lower hydroxyl defect concentration than quartz in igneous rocks. Pre-eruptive and post-depositional loss of hydrogen were hypothesized as the main processes for lowering the initial magmatic concentrations of hydroxyl defects. The aim of this study was to examine the hydroxyl defect concentration of quartz phenocryst fragments from various vertical positions above the base of pyroclastic density current (PDC) deposits. It aims to record the vertical variations of hydroxyl defect concentrations to have an insight into potential post-depositional hydrogen loss of PDC deposits. Ignimbrite-hosted quartz phenocryst fragments were examined from two different ignimbrites in the Bükk Foreland Volcanic Area (North Hungary). Unpolarized micro-FTIR measurements on 23–35 unoriented crystal fragments from each sample were performed representing four different vertical positions of each site. Present results imply that hydroxyl defect concentrations show a pronounced decrease upward from the base of the deposits. The initial ~12 ppm hydroxyl defect concentration decreases to <3 ppm within <10 m from the base. Ignimbrites with contrasting degree of welding are characterized by different hydroxyl defect concentrations of quartz phenocryst fragments at the same height above the base. Thus, post-depositional dehydration is supposed to be the main factor causing the observed vertical decreasing trend. The modeling of post-depositional dehydration by considering typical ignimbrite emplacement temperatures (300–700 °C) and thicknesses (20–50 m) revealed that neither different cooling rates or different crystal diameters could cause the observed decrease in hydroxyl defect concentrations in ignimbrites. Other factors, such as contrasting pre-depositional thermal history, presence of melt- and fluid inclusion, and crack density of crystals could also play an important role in affecting the final hydroxyl defect concentrations.

Danube Bend: Miocene Half-Caldera and Pleistocene Gorge

The Danube Bend, a river curvature, called Visegrad Gorge in its deepest and narrowest part, is one of the most picturesque landscapes in Hungary. Its origin and relief evolution has been a long-standing problem in Hungarian earth sciences. A number of geomorphological theories have been put forward in explaining the valley with a U-shaped planform, which is incised in the surrounding Miocene volcanic mountains. In the past fifteen years, thanks to combined volcanological, geomorphological and geochronological studies, the landscape evolution of the river bend of 5 km diameter has been largely clarified. The present-day U-shaped loop is partly inherited from the horseshoe caldera morphology of Keserűs Hill volcano, a 15-Ma-old andesitic lava dome complex with an eroded central depression open to the north. The formation of the Danube Bend was initiated by river incision that started to remove post-volcanic sedimentary cover in middle or rather late Pleistocene times. These processes in turn were triggered by mountain uplift, climate changes, and drop of the remote erosion base level. The present curvature of the river was controlled by the exhumation of the horseshoe caldera as well as the surrounding resistant volcaniclastic rocks (Visegrad Castle Hill) and a hilltop lava dome (Szent Mihaly Hill). Moreover, a previous meander may have also inherited. The accelerated Late Quaternary erosion and intense dissection has resulted in a “re-birth” of the volcanic relief that exhibits again steep slopes. At present, exposed spectacular rock formations (e.g. Vadallo-kovek) tower above the gorge that belongs to the Danube-Ipoly National Park in Hungary.

Vegetation response to climate forcing during the last glacial maximum and deglaciation in the East Carpathians: attenuated response to maximum cooling and increased biomass burning

The Carpathian Mountains were one of the main mountain reserves of the boreal and cool temperate flora during the Last Glacial Maximum (LGM) in East-Central Europe. Previous studies demonstrated late glacial vegetation dynamics in this area; however, our knowledge on the LGM vegetation composition is limited due to the scarcity of suitable sedimentary archives. Here we present a new record of vegetation, fire and lacustrine sedimentation from the youngest volcanic crater of the Carpathians (Lake St Anne, Lacul Sfânta Ana, Szent-Anna-to) to examine environmental change in this region during the LGM and the subsequent deglaciation. Our record indicates the persistence of boreal forest steppe vegetation ( Pinus sylvestris , Pinus mugo , Pinus cembra , Betula , Salix , Populus , Picea abies ) in the foreland and low mountain zone of the East Carpathians and Juniperus shrubland at higher elevation. We demonstrate attenuated response of the regional vegetation to maximum global cooling. Between ~22,870 and 19,150 cal yr BP we find increased regional biomass burning that is antagonistic with the global trend. Increased regional fire activity suggests extreme continentality likely with relatively warm and dry summers. We also demonstrate xerophytic steppe expansion directly after the LGM, from ~19,150 cal yr BP, and regional increase in boreal woodland cover with Pinus and Betula from 16,300 cal yr BP. Plant macrofossils indicate local (950 m a.s.l.) establishment of Betula nana and B . pubescens at 15,150 cal yr BP, Pinus sylvestris at 14,700 cal yr BP and Larix decidua at 12,870 cal yr BP. Pollen data furthermore hints at the regional presence of some temperate deciduous trees during the LGM ( Fagus sylvatica , Carpinus betulus , Corylus avellana , Fraxinus excelsior , Ulmus ). We also present pollen based quantitative climate reconstruction from this site and discuss its connection with other climate reconstructions and climate modeling results.

A high-resolution Early Holocene-late MIS 3 environmental rock- and palaeomagnetic record from Lake Sf. Ana, Carpathian Mts, Romania

Lacustrine sediments are excellent sources of palaeoenvironmental and palaeoclimaticxa0information because they usually provide continuous and high-resolution records. In centraleasternxa0Europe however lacustrine records that extend beyond the Holocene are rather sparse. Palaeomagnetic records from this region are also insufficiently explored, and usually associatedxa0with terrestrial deposits such as loess. In this context, the lacustrine record of Lake Sf. Ana, axa0volcanic crater lake in the East Carpathians, Romania, provides an important archive forxa0reconstructing past paleomagnetic secular variation in the region from early Holocene to latexa0Marine Isotope Stage (MIS) 3.

D. Jerram: Introducing volcanology—A Guide to Hot Rocks

Plenty of written material is available for students and the interested general audience that provides appropriate information on volcanism. Specific textbooks, formulated rigorously such as Cas and Wrights Volcanic Successions, or put forward in an enjoyable style and logical manner such as Franciss Volcanoes—A Planetary Perspective, can be listed as examples of helpful literature. There are also good methodological achievements such as Volcanic Textures by McPhie et al., or fully illustrated first-hand experience such as Volcanism by Schmincke. Among recent, updated summary textbooks, Hazlett and Lockwoods Volcanoes has already been reviewed on these pages. All the above books, however, are extensive works 300 or 400 pages long, most trying to give all the available information on a wide range of selected topics. In fact, they do not really target the “interested public” so much as the university community and expert volcanologists, who can benefit from these books and hope to find in them most items they need for learning, teaching, or even research. By contrast, Dougal Jerram’s Introducing volcanology— A Guide to Hot Rocks (2011) is written with the obvious design of reaching the widest possible audience: it has a reader-friendly 19×16-cm booklet format only 118 pages long, illustrated throughout with pertinent figures, and including photographs taken on location. Also, in accordance with the publisher’s intentions, the specific terminology is very limited, although a glossary is given at the end containing the most important keywords with a brief explanation. It goes without saying that the book is for the “beginners”, but at the same time with the aim of including all relevant information related to volcanoes. The book comprises 10 chapters, arranged in a typical way: volcanic rocks, how magma forms by melting, plate tectonics and planets, types of volcanism, effusive and explosive eruptions, intrusive activity, effects on life and climate, and monitoring and benefitting from volcanoes. Not only such a simple and logical ordering of topics, but also the language is attractive for the hypothesized “beginner”, exemplified here by some selected sub-chapter titles: how do I start?; melting the Earth; the runny ones: basic flows; raining from the sky—air falls; plumbing the oceans; why Man lives around volcanoes, etc. When reading the text, not only is one convinced that the writer has significant experience in teaching, but also that he holds up-to-date knowledge and skill in most of the presented topics, proven among other Editorial responsibility: K. Németh