In Memoriam

In Memoriam - Willi Dansgaard & Robert Seeman

4D flow pattern of the longest cave in the Eastern Alps (Schönberg-Höhlensystem, Totes Gebirge)

The Schönberg-Höhlensystem (SBH) is not only the longest cave system in the Eastern Alps (length 156 km, depth 1061 m), but a significant proportion of the passages have developed on or just below two surfaces that dip 1.7° to the NE. These so-called "speleogenetic phases" are rarely developed in caves of the Northern Calcareous Alps and have not yet been confirmed by detailed morphological mapping. Furthermore, the deep parts of the cave offer the possibility to study the active epiphreatic zone for a distance of 1.6 km. Detailed morphological mapping shows that the main level at about 1500 m a.s.l. and a second 140 m higher developed as distinct speleogenetic phases, and the dip of the planes to the NE is consistent with palaeo-flow. Isolated vadose trenches formed at saddle points are further evidence. Correlations with other caves at similar altitudes suggest an Upper Miocene to Lower Pliocene age. With few exceptions, a northeastern palaeo-flow can be observed down to about 1050 m a.s.l. However, 100 m above this there appears to have been a late phase with an opposite palaeo-flow direction, and below this altitude this SW palaeo-flow direction prevails. These morphological observations allow us to propose a complex model. During low and moderate flow there is drainage to the north. During floods, a restriction in the north causes backwater and an overflow threshold to the SW is exceeded, and then most of the water flows in this direction. This observation of dual flow behaviour can help to better understand the behaviour of the karst water table and to interpret complex results from tracer experiments. The almost ubiquitous paragenetic features in the SBH are due to sediments derived from the local Upper Jurassic Radiolarite Group. For the evolution of karst plateaus in the Northern Calcareous Alps, these observations support a local and rather radial palaeo-drainage of the Totes Gebirge, as opposed to a through-flow of allogenic waters as is likely for other karst massifs

In Memoriam

In Memoriam - Willi Dansgaard & Robert Seeman

Cuevas de Loess de Austria - un avance

Loess caves account for a negligible amount of Austria's caves only – despite the fact that the areas covered by loess and loess-loam comprise several thousand square kilometres. Loess can be found in the northern and eastern foreland of the Alpine Mountain Range as well as in the Styrian Basin south of the Alps. Only a handful of caves have been mapped so far, concentrated at a few spots. This eye-catching fact documents a certain lack of exploration rather than a general lack of loess caves. According to Striebel (2005) and others most loess caves are formed by piping and gully erosion, initiated by inhomogeneities like disintegrating roots and animal burrows where the infiltrating water causes fast-growing pipe structures, subsequently enlarging to caves that can be entered by cavers.The rate of cave evolution is tremendous. In several cases – so far investigated – the earliest onset of cave formation lies within the early 20th Century. This can be dated as the required gradient was man-made at that time. On the other hand distinctive alterations of the caves took place within 30 years. This can be documented strikingly by comparing old and new cave maps. The crucial points – from a quantitative point of view – for the formation of loess caves are still under fundamental discussion as there are severe differences in local climatic parameters – some of the areas belong to the driest in Austria – lithologies, gradients and human interventions. Furthermore, the role of dissolution of calcitic components enhancing the subsequent erosion remains ambiguous.Las cuevas de loess representan una cantidad insignificante de las cuevas de Austria, a pesar de que las áreas cubiertas por loess y marga de loess abarcan varios miles de kilómetros cuadrados. El loess se encuentra en el antepecho norte y este de la cordillera alpina, así como en la cuenca de Estiria, al sur de los Alpes. Hasta ahora sólo se ha cartografiado un puñado de cuevas, concentradas en unos pocos puntos. Este hecho llamativo documenta una cierta falta de exploración más que una carencia general de cuevas de loess. Según Striebel (2005) y otros, la mayoría de las cuevas de loess se forman por la erosión de tuberías y barrancos, iniciada por inhomogeneidades como la desintegración de raíces y las madrigueras de animales, donde el agua que se infiltra provoca estructuras de tuberías de rápido crecimiento, que posteriormente se amplían hasta convertirse en cuevas en las que pueden entrar los espeleólogos.El ritmo de evolución de las cuevas es tremendo. En varios casos hasta ahora investigados, el inicio más temprano de la formación de cuevas se sitúa a principios del siglo XX. Esto puede fecharse ya que el gradiente necesario fue creado por el hombre en esa época. Por otro lado, las alteraciones distintivas de las cuevas se produjeron en un plazo de 30 años. Esto se puede documentar de forma llamativa comparando los mapas de cuevas antiguos y nuevos. Los puntos cruciales –desde un punto de vista cuantitativo– para la formación de cuevas de loess siguen siendo objeto de un debate fundamental, ya que existen graves diferencias en los parámetros climáticos locales –algunas de las zonas pertenecen a las más secas de Austria–, litologías, gradientes e intervenciones humanas. Además, el papel de la disolución de los componentes calcíticos que potencian la posterior erosión sigue siendo ambiguo

In Memoriam

In Memoriam - Willi Dansgaard & Robert Seeman

A new karren feature: hummocky karren

Karren are small-scale landforms on karst surfaces and many types have been described so far. Here we present an apparently new feature which was found on the Hochschwab karst massive in the Northern Calcareous Alps of Austria. So far only few outcrops each having less than 1 m² within a very restricted area have been found. Morphometric analysis reveals that the karren consist of a randomly distributed, dispersed assemblage of small hummocks and depressions in between. The mean distance between neighbouring hummocks is 4 to 5 cm and the mean height is 0.85 cm. Longitudinal sections are gently sinuous. The occurrences are delimited by thin soil cover with grassy vegetation. The karst features continue below that vegetation cover. Therefore, it is clear that the karren have formed subcutaneously. Corroded fissures where water could infiltrate into the epikarst are absent. The bedrock lithology is Middle Triassic limestone of the Wetterstein Formation in lagoonal facies. Geological structures do not govern the feature. The surface is not a bedding plane and small joints and fractures do not govern the arrangement of the hummocks. Thin section analysis regarding rock texture and dolomite components show that there is no compositional difference between hummocks and depressions. Geochemical analyses show that the limestone is very pure with a very low content of Magnesia. Slightly higher Magnesia contents at the hummock surfaces are significant. The data obtained so far only indicate that some dissolution mechanism but not any rock property governs the irregular array. As there exist no descriptions of comparable features in literature, the name “hummocky karren” is suggested for that type of karren landform

Cosmogenic nuclide dating of cave sediments in the Eastern Alps and implications for erosion rates

Karstic caves are created by water eroding and corroding rocks that can be dissolved. Since both the spring areas of caves (normally at the valley bottom) as well as the recharge is controlled by superficial processes, the morphology of the cave bears strong links to these influences. Lowering of local base levels promotes the development of horizontal phreatic cave passages at progressively lower elevations, resulting in the formation of multi-level karst systems. Upon the next lowering of base level, these upper systems become fossilized, and sediment trapped within them may remain preserved for millions of years. Dating these sediments gives clues regarding the time when the passages were last active, and thus may yield age information for old valley floors. The present paper presents cosmogenic nuclide datings of twelve samples from eight caves in the central part of the Northern Calcareous Alps of Austria. Besides three samples that gave no results, most of the obtained ages are at the Mio-Pliocene boundary or within the Pliocene, as was expected before sampling. No multi-level caves could be sampled at different elevations, thus, the obtained valley deepening rates are averages between the age of sediment deposition and the present-day valley floor. However, the valley deepening rates of 0.12 to 0.21 km/Ma are in accordance to previous findings and corroborate a comparatively slow evolution of base level lowering in the Eastern Alps compared to the fast (Late Quaternary) evolution in the Central and Western Alps

Corrosion morphology and cave wall alteration in an Alpine sulfuric acid cave (Kraushöhle, Austria)

Whereas most karstic caves worldwide are formed by carbonic acid, a small but significant number of sub-surface cavities are the product of sulfuric acid speleogenesis (SAS). In the Eastern Alps, no cave has so far been attributed to this type. In this multidisciplinary study we demonstrate that Kraushöhle in northern Styria was indeed formed by SAS. The cave pattern shows individual chambers, 3D-mazes and blind galleries, as well as typical SAS morphologies such as cupolas, gypsum replacement pockets, corrosion notches and convection niches. “Ceiling pendant drip holes” are described here for the first time and these corrosion features are fully consistent with the SAS model. Other features of Kraushöhle include thick gypsum deposits with strongly depleted δ34S values and other minerals – mostly sulfates – indicating highly acidic conditions. We also studied acid–rock interaction processes giving rise to widespread corrosion and concomitant replacement by gypsum. Petrographic and geochemical analyses reveal the presence of a distinctive alteration layer of highly increased porosity at the interface between the host limestone and the secondary gypsum. Dissolution and replacement of the limestone was fast enough to prevent the development of C and O isotopic alteration halos but resulted in selective leaching of elements. This stable isotope signal is thus different from the pronounced isotope gradient comm observed in CO2-dominated hypogenic caves. Petrographic observations reveal that the limestone–gypsum replacement was a nearly constant volume process

Flow dynamics in a vadose shaft – a case study from the Hochschwab karst massif (Northern Calcareous Alps, Austria)

Karst aquifers are highly vulnerable to contamination due to quick water flow through conduits. Their high heterogeneity and the poorly known infiltration effect of the vadose zone make quantification of recharge processes difficult. This study characterizes the water flow and storage in the upper vadose zone with almost four years monitoring of a permanent stream in a vadose shaft (Furtowischacht). Its small catchment of 4,500 m² is located in a former glaciated high Alpine environment (Hochschwab, Austria). High discharge fluctuations between 0.002 and 19 l/s, relatively high hydrograph recession coefficients, and transit velocities between 0.0015 and 2.4 m/s estimated with salt tracer experiments indicate a highly dynamic discharge behavior. A fast point infiltration through open karren and dolines could be observed for rainfall events and indicates a highly karstified network with a rapid water transmission. Snowmelt periods show only a slower flow component and diffuse infiltration. However, condensation within the conduit system is likely superimposed to this signal. A lumped-parameter rainfall-runoff model is used to simulate the discharge with a dual porosity approach. It indicates a low storage volume, which is in accordance with the estimated storage of 22 m³ (or 5 mm), deduced from the recession analyses. In contrary, the physicochemical parameters argue for some storage capability: 1) After an increase of discharge, electric conductivity reacts with an average delay of 50 min; 2) Partly a piston flow can be recognized. These amounts of water may be stored in the partial soil cover alone and therefore the presence of a hydrologically significant epikarst layer is unclear