Perrierite-(Ce) from the Laacher See tephra, Eifel, Germany, and the modular character of the chevkinite group of minerals

Perrierite-(Ce) crystals from ejecta of the Laacher See volcano, Eifel, in Germany were studied by X-ray single-crystal diffraction and electron microprobe analysis. The composition and crystal structure of this sample is discussed in relation to the known properties of the chevkinite group minerals and related synthetic compounds. Taking into account the modular character of the chevkinite minerals, based on a rutile and a silicate module, the preferred formation of either the perrierite or the chevkinite structure type is correlated with the formal charge of the rutile and silicate modules. The rutile module is expected to carry a negative charge, compensated by a positive charge of the silicate module. On average, the charge modulus is observed to be larger for the chevkinite-type module stacking. It can drop to zero in perrierite-type structures rich in Sr or Ca. In such cases, it is generally not expected to rise above two. The perrierite-(Ce) described in this study crystallizes in space group C2/m. The anisotropic oxygen and rare-earth element displacements observed in this crystal indicate a local domain structure of $$P2_1/a$$ P 2 1 / a symmetry, when compared to the $$P2_1/a$$ P 2 1 / a symmetry of the synthetic perrierite $$\hbox {La}_4\hbox {Mg}_2\hbox {Ti}_3\hbox {O}_8(\hbox {Si}_2\hbox {O}_7)_2$$ La 4 Mg 2 Ti 3 O 8 ( Si 2 O 7 ) 2 .

Simulation of ash clouds after a Laacher See-type eruption

Dated to ca. 13,000 years ago, the Laacher See (East Eifel Volcanic Zone) eruption was one of the largest mid-latitude Northern Hemisphere volcanic events of the Late Pleistocene. This eruptive event not only impacted local environments and human communities but also NH climate. We have simulated the evolution of the fine ash and sulfur cloud of an LSE-type eruption under present-day meteorological conditions that mirror the empirically known ash transport distribution as derived from geological, palaeo-ecological and archaeological evidence linked directly to the Late Pleistocene eruption of the Laacher See volcano. This evidence has informed our experimental set-up and we simulated corresponding eruptions of different injection altitudes (30, 60 and, 100 hPa) with varying emission strengths of sulfur and fine ash (1.5, 15, 100 Tg SO2) and at different days in spring. The chosen eruption dates were determined by the stratospheric wind fields to reflect the empirically observed ash lobes. While it proved difficult to replicate the meteorological conditions that likely prevailed 13,000 years ago, our novel simulations suggest that the heating of the ash plays a crucial role for the transport of ash and sulfate. Depending on the altitude of the injection, the volcanic cloud begins to rotate one to three days after the eruption. The rotation, as well as the additional radiative heating of the fine ash, adds a southerly component to the transport vectors. This ash cloud-generated southerly migration process may at least partially explain why, as yet, no Laacher See tephra has been found in Greenlandic ice-cores. Sulfate transport, too, is impacted by the heating of the ash, resulting in a stronger transport to low-latitudes, later arrival of the volcanic cloud in the Arctic regions and, a longer lifetime. Our models throw new light on the likely behaviour of the ash cloud that darkened European skies at the end of the Pleistocene, and serve as significant input for scenarios that consider the risks associated with re-awakened volcanism in the Eifel.

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.

Sequence completed – palynological investigations on Lateglacial/Early Holocene environmental changes recorded in sequentially laminated lacustrine sediments of the Nahe palaeolake in Schleswig-Holstein, Germany.

The exploration of Lateglacial vegetation history in Schleswig-Holstein is elaborate and comprehensive. Despite being one of the most studied areas, regarding to the Lateglacial, no biostratigraphy covering the complete Lateglacial and Early Holocene periods without hiatus have so far been recovered. In this paper we present a biostratigraphy of the Nahe palaeolake, therewith intending to deal with this desideratum.The special strength of the presented sequence is expressed in the fact that these are the only palynologically investigated sequentially annual laminated limnic sediments of the Lateglacial in Schleswig-Holstein. These laminated sediments, as well as radiocarbon dating of botanical macrofossils and three geochemically confirmed cryptotephra layers (Laacher See Tephra, Vedde Ash and Saksunarvatn Ash), provide excellent chronological control and allow for a Europe-wide correlation. Particularly important is a complete discussion of the vegetation history and the spatial proximity to Late Palaeolithic sites, which renders it possible to evaluate potential human-environment-interaction long before classical palynological human indicators occur.

Small shards and long distances – three cryptotephra layers from the Nahe palaeolake including the first discovery of Laacher See Tephra in Schleswig-Holstein (Germany)

Investigations of Lateglacial to Early Holocene lake sediments from the Nahe palaeolake (northern Germany) provided a high-resolution palynological record. To increase the temporal resolution of the record a targeted search for cryptotephra was carried out on the basis of pollen stratigraphy. Three cryptotephra horizons were detected and geochemically identified as Saksunarvatn Ash, Vedde Ash and Laacher See Tephra. Here we present the first geochemically confirmed finding of the ash from the Laacher See Eruption in Schleswig-Holstein – extending the so far detected fallout fan of the Lateglacial eruption further to the North-West. These finds enable direct stratigraphical correlations and underline the potential of the site for further investigations.