Laacher See Tephra Research Articles

Penetration Resistance of Laacher See-tephra Andosols—Evaluating Rooting Conditions of Undisturbed and Excavated Forest Soils in SW-Germany

This study discusses penetration resistance (PR) of forested Pumice-Andosol sites. PR, a key soil property influencing root growth and elongation, exerts a substantial influence on ecological site quality and tree growth. Andosols were expected to show low PR because of their unique characteristics (low bulk density, loose soil matrix). Five sites, two undisturbed and three backfilled, were sampled. The latter result from pumice excavation and were examined to quantify potential PR alterations in the aftermath of backfilling and pumice removal. Penetrologger sampling on undisturbed sites showed mean PR not exceeding 3 MPa, a literature-based, critical threshold restricting root growth, in the upper 0.80 m, indicating conditions fostering tree rooting. Backfilled sites mostly exhibited increased (> 3 MPa) PR, leading to rooting restrictions even beginning at −0.21 m. Deviations from undisturbed soils range from −15.6 to +109.3% depending on depth and age of the backfilled site. Furthermore, GIS-based data interpolation helped to identify spatial PR patterns and allowed a direct comparison before/after backfilling at one site. Statistical analysis revealed significantly altered PR after backfilling, while a concluding ANOVA provided at least significant governing factors (depth, area, clay + silt content, soil organic matter), albeit with only small effect sizes.

Laacher See tephra discovered in the Bohemian Forest, Germany, east of the eruption

Abstract We present a geochemically confirmed finding of the Laacher See tephra (LST), directly east of the Laacher See volcano (LSV). European lake sediment (Rachelsee, Germany) contains the time period of the Laacher See volcanic explosion (LSE) ca. 12900 yr cal BP in the East Eifel volcanic field. This eruption significantly affected the local environment but its impact in regions far east from its source is poorly known. The lake sediment sequence showed an enhancement in magnetic susceptibility and an increase in concentration in niobium and phosphorus. These enhancements correlated with direct tephra particle observations whose geochemical analysis compared well with the published LST data from proximal sites. Detailed analyses revealed a most likely match with tephra known to have been deposited during the middle phase of the eruption. We suggest that contrary to other published studies, the LST cloud traveled directly east, as far as 470 km, from the volcano,. The pollen record shows minimal change during the tephra deposition, thus indicating that the LSE had no noticeable influence on vegetation in eastern Bavaria and the southern part of the Czech Republic. The discovery of the LST at Rachelsee, opens the potential of further tephrochronological studies in regions to the east of the LSV.

Late Glacial sediments of the Stará Jímka paleolake and the first finding of Laacher See Tephra in the Czech Republic

The Late Glacial sedimentary sequence of the Stara Jimka paleolake (Bohemian Forest, Czech Republic) is characterized by the prevalence of detrital minerals with an elevated proportion of organic matter and abundant diatom valves in relatively warm periods. The mineral debris originated mainly from local migmatites and mica-schists (or glacial and deluvial deposits derived from the same material). Low background contents of CaO (< 0.20 wt%) and Na2O (< 0.50 wt%) reflect chemical weathering. Correlation analysis of trace elements shows that the mineral debris concentrates Rb, Cs, Ga, Cr, Zr, Hf, light rare earth elements, Th, U, Pb, Ba, Sr and weakly Zn, whereas Mo, Co, Se, As, Ni, Cu, Br and weakly Au are allocated predominantly to sulphides and organic matter. The sequence contains a continuous horizon with the Laacher See Tephra (LST), causing contrasting maxima of Na, Ca, Cl and Nb in bulk composition. While the phonolitic tephra corresponds to the lower part of the middle LST unit it also contains phosphorus-rich relicts of older sediments with small euhedral (air-transported) volcanic crystals. Such sediments may have occurred in depressions at an older volcano prior to the major Laacher See eruption (~ 12,880 cal. BP).

Zoning and exsolution in alkali feldspars from Laacher See volcano (Western Germany): constraints on temperature history prior to eruption

Compositional zoning and exsolution patterns of alkali feldspars in carbonatite-bearing cognate syenites from the 6.3 km3 (D.R.E) phonolitic Laacher See Tephra (LST) deposit in western Germany (12.9 ka) are reported. These rocks represent the cooler outer portion and crystal-rich products of a cooling magma reservoir at upper crustal levels. Major and trace-element difference between cores and rims in sanidine crystals represent two generations of crystal growth separated by unmixing of a carbonate melt. Trace-element differences measured by LA–ICP–MS are in accordance with silicate–carbonate unmixing. Across the core–rim boundary, we extracted gray-scale profiles from multiple accumulations of back-scattered electron images. Gray scales directly represent K/Na ratios owing to low concentrations of Ba and Sr (< 30 ppm). Diffusion gradients are modeled to solve for temperature using known pre-eruptive U–Th zircon ages (0–20 ky) of each sample (Schmitt et al., J Petrol 51:1053–1085, 2010). Estimated temperatures range from 630 °C to 670 °C. For the exsolution boundaries, a diffusive homogenization model is constrained by the solvus temperature of ~ 712_725 °C and gives short time scales of only 15–50 days. Based on our results, we present a model for the temperature–time history of these rocks. The model also constrains the thermal variation across the cooling crystal-rich carapace of the magma reservoir over 20 ka and suggests a thermal reactivation of cumulates, the cooling carapace, and probably the entire system only a few years prior to the explosive eruption of the remaining molten core of the phonolitic magma reservoir.

The Laacher See Tephra discovered in southernmost Sweden

ABSTRACTWe present the first geochemically confirmed finding of the Laacher See Tephra (LST) on the Swedish mainland, now the northernmost extension of the LST. Sediments were sampled at the Körslättamossen fen, southernmost Sweden, and a high‐concentration cryptotephra occurrence (&gt;65 000 shards cm−3) of the LST was found in a sequence of calcareous gyttja. Tephra identification was confirmed by geochemical analysis using field‐emission electron probe microanalysis and through comparison of the results with published LST data from proximal sites and distal sites north‐east of Laacher See. The LST has previously been divided into eruption phases suggested to have spread in several dispersal fans, but it was not possible to confidently determine the phase of the tephra here closer than to the MLST or ULST. The finding of the LST presented here further strengthens the potential of tephrochronological studies in the south Scandinavian region.

Copper isotope behavior during extreme magma differentiation and degassing: a case study on Laacher See phonolite tephra (East Eifel, Germany)

Copper (Cu) isotopic analyses were performed on a set of samples from the Laacher See tephra (LST) (Eifel, Germany) to investigate whether Cu isotopes are fractionated during extreme magma differentiation and degassing. The LST represents a continuous fractional crystallization series from parental basanite through mafic to highly differentiated phonolites. Samples analyzed here include phonolites of variable degrees of differentiation, phonolite–basanite hybrid rocks formed by mixing basanite and phonolite magmas, and basanite-derived mega-crystals (i.e., clinopyroxene, amphibole, phlogopite). In addition, we analyzed a series of mafic parental lavas from surrounding volcanic centers to constrain the Cu isotopic features of the Eifel mantle. Mafic phonolites show strong depletion in Cu compared to their parental basanites from ~50 to ~3 ppm, indicating sulfide fractionation during the basanite-to-phonolite differentiation. Mass balance calculations, based on the most Cu-rich hybrid rock (δ65Cu = −0.21 ‰, [Cu] = 46.2 ppm), show that the parental basanite magmas have δ65Cu of ca. −0.21 ‰, lighter than those of the mafic phonolites (~0.11 ‰). This suggests that sulfide fractionation preferentially removes the lighter Cu isotope (63Cu) in S-saturated magmas. By contrast, all phonolites have a limited range of Cu contents (1.1 to 4.0 ppm) with no systematic variations with S, suggesting that Cu is not controlled by sulfide fractionation during the evolution of mafic to highly differentiated phonolites. The identical δ65Cu values (0.11 ± 0.03 ‰, 2SD, n = 10) of the phonolites, irrespective of highly diverse composition and extents of differentiation, indicate that fractional crystallization of silicates (e.g., plagioclase, sanidine, amphibole, pyroxene, olivine), Fe–Ti-oxides and phosphate (e.g., apatite) generates insignificant Cu isotope fractionation. The lack of correlations between δ65Cu and volatile contents (e.g., S, Cl) in the LST sequence implies that volcanic degassing causes no detectable Cu isotope fractionation of igneous rocks. Eifel basalts and mega-crystals have variable δ65Cu (−0.18 to 0.21 ‰) that are uncorrelated to MgO and Cu, suggesting that such variations were not caused by differentiation but reflect the Cu isotopic heterogeneity of the Eifel mantle source due to metasomatism by fluids derived from hydrothermally altered oceanic lithosphere.

Late Glacial and Holocene plant cover in Węgliny, Lubsza Plain, south-west Poland, based on pollen analysis

ABSTRACT Late Glacial (since Oldest Dryas) and Holocene (to Subatlantic) changes of vegetation at the Węgliny site (south-west Poland) are reconstructed based mainly on pollen analysis of five cores from the palaeobasin (anaerobic sediments). The chronology of the described events is based on palynological comparison with the Lubsza Plain environs, based on LPAZs from several published pollen diagrams on 14C data, and multiple cryptotephra levels determined in the Węgliny profiles. The Węgliny record integrates well into the north European Holocene and Late Glacial biostratigraphic framework. The Węgliny site is the next (fourth) locality in Poland where the Laacher See Tephra (LST) horizon within the Allerød chronozone was identified.

Tracing the Laacher See Tephra in the varved sediment record of the Trzechowskie palaeolake in central Northern Poland

Tephrochronological studies of partly varved sediments of Trzechowskie palaeolake in central Northern Poland led to the finding of the Late Allerød Laacher See Tephra (LST) from the Eifel Volcanic Field for the first time in a very distal site ca 840 km ENE from its volcanic source. The detection of glass shards of the LST involved a comprehensive combination of techniques, i.e. biostratigraphical constrains, high-resolution μ-XRF core scanning and areal μ-XRF mapping of impregnated sediment slabs as well as detailed visual inspection of sediments. The major element chemistry of volcanic glass confirmed the Laacher See Tephra composition in Trzechowskie palaeolake sediments suggesting a deposition from the Middle Laacher See Tephra (MLST-C) or Upper Laacher See Tephra (ULST) dispersal fans. The finding of the LST in this palaeolake enables direct synchronisation with other high-resolution archives in north-central Europe (i.e., Lake Meerfelder Maar, Rehwiese palaeolake) to investigate regional variations of environmental responses at the onset of the Younger Dryas along a West-East transect through north-central Europe.

Tephrostratigraphy of a Lateglacial lake sediment sequence at Węgliny, southwest Poland

This paper presents the first late Quaternary locality in the present-day territories of Poland where multiple cryptotephra layers have been identified. Located near Węgliny in southwest Poland, study of the Lateglacial gyttja deposits reveals the presence of at least four non-visible tephra horizons. Electron microprobe and laser-ablation ICPMS analysis of glass shards suggests products from at least two Icelandic volcanic centres: Katla and Snæsfellsness. Of particular importance is the discovery of two eruptions believed to originate from the east Eifel volcanic field within the Allerød chronozone. One correlates with the well documented Laacher See Tephra (LST) but the second horizon, herein designated T642/T655 would appear to represent an earlier precursor eruption. The chemical composition of the LST and the precursor tephra both appear to match to the Upper Laacher See Tephra (ULST) phase, which previously was thought to have dispersed not to the northeast but in a southerly direction, towards the Alpine foreland. This indicates the eruption dynamics of the Laacher See are more complex than hitherto recognised.

Late Pleistocene to Early Holocene natural and human influenced sediment dynamics and soil formation in a 0-order catchment in SW-Germany (Palatinate Forest)

This paper presents the dynamics of sedimentation processes and soil development of a steeply sloping 0-order catchment in the sandy Lower Bunter of the south-western mid-range mountains in the Palatinate Forest (Germany) during the transition period from the Late Glacial to the Early Holocene. Field investigations, chemical, physical, micromorphological and anthracological analyses revealed a complex palaeosol-sediment sequence along the thalweg of a dry valley, where a significant amount of the sediment from the adjacent slopes had been captured. The deposition of aeolian sands in the lowermost sediment layer took place in the early Late Glacial. The subsequent sediments were deposited by slope-wash and aeolian processes. It contains a higher amount of silt and dates from the Allerød. The occurrence of Laacher See Tephra (LST) indicates that this sediment has been near the surface around 12,900 cal. BP. It also shows characteristics of palaeosols similar to the Usselo/Finow soils in north-eastern Germany. In the overlying material, the amount of root remnants, other organic matter and rounded bone fragments possibly indicates the presence of people in this area. On top, alternating reddish brown, coarse to fine sand and small, partly rounded stones with some small intercalated aggregations of humic material rich in charcoal dating to between 11,000 and 12,000 cal. BP were deposited. The layers are overlain by clearly visible and evenly distributed wavy clay-illuviation bands typical for a Luvisol. In the upper metre, a Cambisol has developed. The sediment structure shows typical features of a flash-flood event in the Preboreal. The stratigraphy suggests that phases of sedimentation caused by water and aeolian erosion took place in the Allerød, Younger Dryas, and Preboreal. Discussion considers climate driven natural processes as well as the possibility that the manipulation of forest vegetation by fire through sedentary Mesolithic hunter–gatherer groups created open areas and enabled intensive soil erosion at a local scale.

Testing a portable laser-induced breakdown spectroscopy system on geological samples

This paper illustrates the potentialities of a home-made portable LIBS (laser-induced breakdown spectroscopy) instrument in Earth sciences, more particularly in geochemically recognizing (i) tephra layers in lacustrine sediments and (ii) fossilization processes in ammonites. Abundances for selected lines of Al, Ca, Fe, Ti, Ba and Na were determined in lacustrine chalk sediments of the Jura, where the Laacher See Tephra (LST) layer is recorded. A statistical treatment of elemental maps produced from the section of a sedimentary column containing the LST event allows instrumental conditions to be optimized. Accumulating spectra from close shot positions gives better results than multiplying shots at the same location. A depth profile method was applied to study ammonite fossilization (pyritization, phosphatization) processes. Depth variations of Fe, Ca, Al intensities, and Fe/Ca and Al/Ca ratios provide indications about pyritization, but phosphatization processes cannot be determined with our device.

A Younger Dryas varve chronology from the Rehwiese palaeolake record in NE-Germany

The first 1400-year floating varve chronology for north-eastern Germany covering the late Allerød to the early Holocene has been established by microscopic varve counts from the Rehwiese palaeolake sediment record. The Laacher See Tephra (LST), at the base of the studied interval, forms the tephrochronological anchor point. The fine laminations were examined using a combination of micro-facies and μXRF analyses and are typical of calcite varves, which in this case provide mainly a warm season signal. Two varve types with different sub-layer structures have been distinguished: (I) complex varves consisting of up to four seasonal sub-layers formed during the Allerød and early Holocene periods, and, (II) simple two sub-layer type varves only occurring during the Younger Dryas. The precision of the chronology has been improved by varve-to-varve comparison of two independently analyzed sediment profiles based on well-defined micro-marker layers. This has enabled both (1) the precise location of single missing varves in one of the sediment profiles, and, (2) the verification of varve interpolation in disturbed varve intervals in the parallel core. Inter-annual and decadal-scale variability in sediment deposition processes were traced by multi-proxy data series including seasonal layer thickness, high-resolution element scans and total organic and inorganic carbon data at a five-varve resolution. These data support the idea of a two-phase Younger Dryas, with the first interval (12,675–12,275 varve years BP) characterised by a still significant but gradually decreasing warm-season calcite precipitation and a second phase (12,275–11,690 varve years BP) with only weak calcite precipitation. Detailed correlation of these two phases with the Meerfelder Maar record based on the LST isochrone and independent varve counts provides clues about regional differences and seasonal aspects of YD climate change along a transect from a location proximal to the North Atlantic in the west to a more continental site in the east.

Contributions of different parent materials in soils developed from periglacial cover‐beds

Soils frequently develop from mixtures of different parent materials. We quantified the contributions of different parent materials to the substrate for recent soil development using trace metal concentrations and Pb isotope ratios as input data for end‐member mixing analyses (EMMAs). We examined six transects (320–775 m) at two sites in the Rhenish Slate Mountains. Soil types ranged from acid Cambisols to stagnic Luvisols developed from periglacial cover‐beds. Sixteen O, 11 A, 120 B and 10 C horizons were analysed for total trace metal concentrations and partly also 206Pb:207Pb ratios. Most metal concentrations in the B horizons were in the background range, except for Pb, which partly had elevated concentrations of up to 135 mg kg−1. The depth distribution of metal concentrations and 206Pb:207Pb ratios suggested that metals deposited from the atmosphere had hardly reached the B horizons. A principal component analysis (PCA) of the trace element concentrations in the 120 B horizons identified four main metal sources of the B horizons, which we interpreted as bedrock (slate), loess, Laacher See tephra (LST) resulting from the last volcanic eruption in the Eifel mountains and ore veins. The slate was characterized by Cr and Zn, the loess by Zr, the LST by Nb and the ore veins by Pb. Based on EMMAs with four end‐members using two different sets of tracers (Set 1: concentration ratios of Zr:Cr, Nb:Cr, Pb:Cr, Set 2: Zr:Zn, Nb:Zn, and Pb:Zn), slate, loess and LST contributed, on average, 39–40, 22–24 and 37–38%, respectively, at Site 1 and 19–21, 53–63 and 18–26%, respectively, at Site 2. In contrast, the ore contribution was consistently estimated at 0%. An additional EMMA with two end‐members based on the 206Pb:207Pb ratios estimated the contribution of the ore at 0.02%. We conclude that EMMAs based on trace element concentrations and isotope ratios provide a tool for determining the contribution of different parent materials to the substrate from which soils develop, at least at a small regional scale and if an appropriate tracer that distinguishes all the considered substrates is found.

Reconstruction of the Allerød vegetation of the Neuwied Basin, western Germany, and its surroundings at 12,900 cal b.p.

During the late-glacial eruption of the Laacher See volcano 12,900 b.p. the whole area of the Neuwied Basin, middle Rhine region, was covered by several metres of the Laacher See Tephra (LST) damaging but also partly conserving the former vegetation. This gave the unique opportunity to study plant remains in situ and to estimate the spatial biodiversity of plant taxa within the area investigated at the end of the last glacial as if in a snapshot of 12,900 years ago. Different kinds of plant material can be found because of different preservation conditions namely imprints, charcoal and waterlogged remains. Investigations of this material from several places within the Neuwied Basin and the Brohl valley north of it allowed the reconstruction of the former vegetation at different scales from local to regional. This resulted in a large scale draft of a vegetation map of the studied area also based on the distribution and the stage of soil development at that time. As to whether thermophilous trees were already present is discussed but largely rejected.

North European last glacial–interglacial transition (LGIT; 15–9 ka) tephrochronology: extended limits and new events

AbstractHigh‐precision correlation of palaeoclimatic and palaeoenvironmental records is crucial for testing hypotheses of synchronous change. Although radiocarbon is the traditional method for dating late Quaternary sedimentary sequences, particularly during the last glacial–interglacial transition (LGIT; 15–9 ka), there are inherent problems with the method, particularly during periods of climate change which are often accompanied by major perturbations in atmospheric radiocarbon content. An alternative method is the use of tephras that act as time‐parallel marker horizons. Within Europe, numerous volcanic centres are known to have erupted during the LGIT, providing considerable potential for high‐precision correlation independent of past radiocarbon fluctuations. Here we report the first identification of the Vedde Ash and Askja Tephra in Ireland, significantly extending the known provenance of these events. We have also identified two new horizons (the Roddans Port Tephras A and B) and tentatively recognise an additional horizon from Vallensgård Mose (Denmark) that provide crucial additional chronological control for the LGIT. Two phases of the Laacher See Tephra (LST) are reported, the lower Laacher See Tephra (LLST) and probably the C2 phase of the Middle Laacher See Tephra (MLST‐C2) indicating a more northeasterly distribution of this fan than reported previously. Copyright © 2006 John Wiley &amp; Sons, Ltd.

Environmental and climatic changes in the Jura mountains (eastern France) during the Lateglacial–Holocene transition: a multi-proxy record from Lake Lautrey

This paper presents a multi-proxy reconstruction of the climatic and environmental changes during the Last Glacial–Interglacial transition as recorded by a sediment sequence from Lake Lautrey (Jura, eastern France). This reconstruction is based on analysis of pollen, chironomid, organic matter, oxygen-isotope, mineralogical, magnetic susceptibility and inferred lake-level data at a high temporal resolution. The chronology is derived using AMS radiocarbon dates, the position of the Laacher See Tephra (LST), and of correlation between the Lautrey and GRIP oxygen-isotope records. This data set reveals a detailed sequence of environmental changes in the Jura mountains from Greenland Stadial 2a to the early Holocene. Biotic and abiotic indicators allow the recognition of major abrupt changes associated with the GS-2a/GI-1e, GI-1a/GS-1 and GS-1/Preboreal transitions, and other minor fluctuations related to the cold events GI-1d, GI-1b and the Preboreal oscillation (PBO). They also suggest additional cooling spells at ca 14,550 and 14,350 cal yr BP (Intra-Bølling Cold Periods), at ca 13,500 and ca 12,700 cal yr BP just before the GS-1 onset, and at ca 11,350 cal yr BP just before the PBO, as well as an intriguing brief warming episode within GS-1 at ca 12,080 cal yr BP. Summer temperature increased by ca 5 °C at the start of GI-1e, and by 1.5–3 °C at the Holocene onset, while it decreased by ca 3–4 °C at the beginning of GS-1. Major changes in local hydrology and in seasonality appear to be also associated with the GS-2a/GI-1e, GI-1a/GS-1 and GS-1/Preboreal transitions. Pollen and abiotic indicators suggest a greater sensitivity of the vegetation cover to climatic oscillations during the first part of the Lateglacial Interstadial than during the second part (after ca 13,700 cal yr BP), when a closed forest had been restored in this area. By contrast, the restoration of forest cover took less than 300 yr after the end of GS-1. At the beginning of GI-1e and GS-1, no lag occurs (within the sampling resolution of 20–50 yr) in the responses of aquatic (chironomids) and terrestrial (pollen) ecosystems, while, at the onset of the Holocene, the response of the vegetation appears slightly delayed in comparison with that of the chironomid community. Finally, the recognition of two successive tephra layers, which were deposited just before the LST at ca 12,950 cal yr BP and which originated from Le Puy de la Nugère (Massif Central, France), provides an additional tephrochronological tool for correlation between Lateglacial European sequences.

Late Glacial and Holocene history of former Salziger See, Central Germany, and its climatic and environmental implications

An 8.40 m long sediment sequence from the Salziger See basin, Central Germany, was investigated by a multi-disciplinary approach including chronological, sedimentological, geo- and biogeochemical methods. Radiocarbon dating, conducted on ten samples of aquatic and terrestrial fossil remains, and the occurrence of the Laacher See Tephra (LST) reveal that the sediment sequence comprises the Late Glacial and Holocene lake history since ca. 13,800 cal. year BP. This onset of lacustrine sedimentation is almost 7,000 years earlier as assumed so far. The geo- and biogeochemical data indicate distinct variations throughout the Late Glacial, which can be correlated with cold and warm periods, such as the Oldest Dryas, the Bolling, the Allerod, and the Younger Dryas. During most of the Holocene, minor variations in the geo- and biogeochemical data and a high carbonate content due to the formation and precipitation of autochthonous carbonate in the lake indicate relatively stable lacustrine conditions. A slight change in the sedimentary conditions between 6,700 and 4,000 cal. year BP, with lower deposition of carbonate and fine material, can be traced back to enhanced subrosion in the basin. Increased deposition of coarser sediments and a high accumulation of heavy metals document intensive human activity in the region during the past ca. 1,000 years.

Experimental constraints on storage conditions in the chemically zoned phonolitic magma chamber of the Laacher See volcano

Phase relations of three samples of the Laacher See Tephra (LST) have been determined experimentally as a function of temperature (760 to 880 °C), pressure (200, 300 and 400 MPa), water content of the melt and oxygen fugacity (ƒO2). The crystallization experiments were carried out at ƒO2=NNO buffer and at NNO=+ 2.3 log units. The melt water contents varied between 6 and more than 8 wt% H2O, corresponding to water-undersaturated and water saturated conditions respectively. The synthetic products are compared to the natural phases to constrain pre-eruptive conditions in the Laacher See magma chamber. The major phases occurring in the LST have been reproduced. The stability of hauyne is favoured at high ƒO2 (≈NNO + 2.3). The CaO contents in melt and plagioclase synthesized under water-saturated conditions are significantly higher than in the natural phases, implying that most of the differentiation of the phonolites took place under water-undersaturated conditions. However, this does not exclude the presence of a S-, Cl- and CO2-rich fluid phase in the upper parts of the magma chamber. The phase relationships and the TiO2 contents of melts show that the temperature was lower than 760 °C in the upper part of the magma column (probably down to 720 °C in the most differentiated levels) and that temperatures above 840–860 °C prevailed in the lower part. The variation of the XMg of ferromagnesian minerals observed in both natural and experimental phases reflects the strong variations in ƒO2 in the lower magma chamber just prior to eruption (probably variation of about 2 log units). The most probable explanation for these ƒO2 variations is the injection of an oxidized alkali-rich magma, containing Mg-rich phenocrysts, at the base of a chemically zoned and more reduced magma column prior to eruption. Although the amount of injected magma may not have been very important, it was sufficient to change the ƒO2 conditions locally, explaining the heterogeneous XMg of ferromagnesian minerals and the formation of hauyne at the base of the chamber.

The potential of OSL and TL for dating Lateglacial and Holocene dune sands tested with independent age control of the Laacher See tephra (12 880 a) at the Section `Mainz-Gonsenheim'

Optically stimulated luminescence (OSL) and Thermoluminescence (TL) are applied in this study to date a Lateglacial and Holocene aeolian sediment sequence. Quartz and potassium rich feldspars extracted from dune sands from western Germany were dated using both multiple-aliquot (MA) and single-aliquot (SA) protocols for luminescence dating. This particular dune section was chosen for this test study, because an independent age control is provided by a horizon of the Laacher Seetephra (12,880 a). In contrast to the results for potassium feldspars, which show underestimation of up to 25%, the quartz fraction provides promising results with respect to the presumed geological ages.

Evolution and environmental impacts of the eruption of Laacher See Volcano (Germany) 12,900 a BP

Laacher See Volcano (LSV), 40 km south of Bonn, explosively erupted ca. 6.3 km3 of chemically strongly zoned phonolite magma probably during spring, 12,900 years ago, the resulting eruption column having reached at least 20 km in height. The bulk of the Laacher See Tephra (LST) was deposited east of the volcano within the Neuwied Basin. LST ashes form the most important stratigraphic marker in Lateglacial deposits over much of Central Europe. A minimum of 2 Mt total S was calculated to have been released during the eruption by comparing pre- and posteruptive volatile concentrations in glass inclusions and pumice matrix glasses. Because a separate S-bearing vapor phase was probably present in the magma prior to eruption as indicated by the high melt-H2O contents close to saturation level, the actual amount of S released during the eruption, could have significantly exceeded 2 Mt. The sulfuric acid aerosol layer resulting from the massive stratospheric S-input probably resided in the stratosphere for years and most likely had a significant impact on climate and thus the environment. Increased precipitation in central Europe and/or impairment of the vegetation cover for several years is suggested by several proxies, especially increased sediment supply into lakes. Proximal to the eruptive center, major environmental impacts include an initial blast that felled trees up to 4 km away from vent. Fast deposition of huge tephra volumes led to the complete disruption of Rhine River within the lower Neuwied Basin and the damming up of a lake ca. 140 km2 in areal extent. Sudden collapse of the temporary tephra dam caused a catastrophic flood wave downstream whose deposits are recognized as far north as Bonn. Reworking of unconsolidated tephra deposits over several 100 km2 was widespread and extensive, generating abundant lahars and flood plain deposits. A braided-river system, established in Neuwied Basin, probably persisted up to several years. Recent reports for a second eruption of LSV are not confirmed.