Fifteen days of continuous activity survey at Stromboli volcano, Italy, in late September 2000: Doppler radar, seismicity, infrared, soil humidity, and mapping of the crater region

The intention of our study was to gain new insight into the complex interplay between different types of eruption of the Stromboli volcano by combining detailed field observation with different geophysical methods. We recorded more than 600 eruptions by use of continuous Doppler radar measurements. We detected the onset of the seismic precursor and the beginning of the visible eruption by use of seismic and infrared data. Two soil samples per day were used to monitor the effect of humidity on the eruptive style. We mapped the crater region as a reference base for the long-term morphological changes of the active region and for the exact positions of our measurement systems. Two distinct types of eruption were distinguished from each other on the basis of seismic and radar data - short, wide-angle Strombolian explosions and pulsating, sharp angle fountain-like eruptions. Data and visual observations imply that weather conditions significantly effect volcanic activity. We also interpret the intensification of eruptive activity during our field study as replenishment of the reservoir with a new batch of magma in late September 2000.     

Late Cretaceous reactivation of major crustal shear zones in northern Namibia: constraints from apatite fission track analysis

Namibia's passive continental margin records a long history of tectonic activity since the Proterozoic. The orogenic belt produced during the collision of the Congo and Kalahari Cratons in the Early Proterozoic led to a zone of crustal weakness, which became the preferred location for tectonism during the Phanerozoic. The Pan-African Damara mobile belt forms this intraplate boundary in Namibia and its tectonostratigraphic zones are defined by ductile shear zones, where the most prominent is described as the Omaruru Lineament–Waterberg Thrust (OML–WT). The prominance of the continental margin escarpment is diminished in the area of the Central and Northern Zone of the Damara belt where the shear zones are located. This area has been targeted with a set of 66 outcrop samples over a 550-km-long, 60-km-broad coast-parallel transect from the top of the escarpment in the south across the Damara sector to the Kamanjab Inlier in the north. Apatite fission track age and length data from all samples reveal a regionally consistent cooling event. Thermal histories derived by forward modelling bracket this phase of accelerated cooling in the Late Cretaceous. Maximum palaeotemperatures immediately prior to the onset of cooling range from ca. 120 to ca. 60 °C with the maximum occurring directly south of the Omaruru Lineament. Because different palaeotemperatures indicate different burial depth at a given time, the amount of denudation can be estimated and used to constrain vertical displacements of the continental crust. We interpret this cooling pattern as the geomorphic response to reactivation of basement structures caused by a change in spreading geometry in the South Atlantic and South West Indian Oceans.     

Late Pleistocene fluvial dynamics in the Hochrhein Valley and in the Upper Rhine Graben: chronological frame

During the Pleistocene, the Rhine glacier system acted as a major south–north erosion and transport medium from the Swiss Alps into the Upper Rhine Graben, which has been the main sediment sink forming low angle debris fans. Only some aggradation resulted in the formation of terraces. Optically stimulated luminescence (OSL) and radiocarbon dating have been applied to set up a more reliable chronological frame of Late Pleistocene and Holocene fluvial activity in the western Hochrhein Valley and in the southern part of the Upper Rhine Graben. The stratigraphically oldest deposits exposed, a braided-river facies, yielded OSL age estimates ranging from 59.6 ± 6.2 to 33.1 ± 3.0 ka. The data set does not enable to distinguish between a linear age increase triggered by a continuous autocyclical aggradation or two (or more) age clusters, for example around 35 ka and around 55 ka, triggered by climate change, including stadial and interstadial periods (sensu Dansgaard–Oeschger cycles). The braided river facies is discontinuously (hiatus) covered by coarse-grained gravel-rich sediments deposited most likely during a single event or short-time period of major melt water discharge postdating the Last Glacial Maximum. OSL age estimates of fluvial and aeolian sediments from the above coarse-grained sediment layer are between 16.4 ± 0.8 and 10.6 ± 0.5 ka, and make a correlation with the Late Glacial period very likely. The youngest fluvial aggradation period correlates to the beginning of the Little Ice Age, as confirmed by OSL and radiocarbon ages.     

Isotopic evidence (Sr/Sr, δLi) for alteration of the oceanic crust at deep-rooted mud volcanoes in the Gulf of Cadiz, NE Atlantic Ocean

The chemical and isotopic composition of pore fluids is presented for five deep-rooted mud volcanoes aligned on a transect across the Gulf of Cadiz continental margin at water depths between 350 and 3860 m. Generally decreasing interstitial Li concentrations and ⁸⁷Sr/⁸⁶Sr ratios with increasing distance from shore are attributed to systematically changing fluid sources across the continental margin. Although highest Li concentrations at the near-shore mud volcanoes coincide with high salinities derived from dissolution of halite and late-stage evaporites, clayey, terrigenous sediments are identified as the ultimate Li source to all pore fluids investigated. Light δ⁷Li values, partly close to those of hydrothermal vent fluids (δ⁷Li: +11.9‰), indicate that Li has been mobilized during high-temperature fluid/sediment or fluid/rock interactions in the deep sub-surface. Intense leaching of terrigenous clay has led to radiogenic ⁸⁷Sr/⁸⁶Sr ratios (0.7106) in pore fluids of the near-shore mud volcanoes. In contrast, non-radiogenic ⁸⁷Sr/⁸⁶Sr ratios (0.7075) at the distal locations are attributed to admixing of a basement-derived fluid component, carrying an isotopic signature from interaction with the basaltic crust. This inference is substantiated by temperature constraints from Li isotope equilibrium calculations suggesting exchange processes at particularly high temperatures (>200 °C) for the least radiogenic pore fluids of the most distal location.Advective pore fluids in the off-shore reaches of the Gulf of Cadiz are influenced by successive exchange processes with both oceanic crust and terrigenous, fine-grained sediments, resulting in a chemical and isotopic signature similar to that of fluids in near-shore ridge flank hydrothermal systems. This suggests that deep-rooted mud volcanoes in the Gulf of Cadiz represent a fluid pathway intermediate between mid-ocean ridge hydrothermal vent and shallow, marginal cold seep. Due to the thicker sediment coverage and slower fluid advection rates, the overall geochemical signature is shifted towards the sediment-diagenetic signal compared to ridge flank hydrothermal environments.     

GGR Critical Review of Analytical Developments in 2004–2005

In 2005 Geostandards and Geoanalytical Research embarked upon a new initiative for its readers. Key researchers in various fields of geoanalytical technique development and their application were identified and invited to provide reviews pertinent to their expertise. As noted in the first of these publications "…instead of revisiting the historical context or decades of development in each analytical technique, the goal here has been to capture a snapshot of "hot topics" across a range of fields as represented in the… literature" (Hergt et al . 2005). Rather than prepare an annual review, a decision was taken earlier this year to provide a biennial summary of progress and accomplishments, in this case for the years 2004–2005. The principal techniques employed in Earth and environmental sciences are covered here, and include laser ablation and multicollector ICP-MS, ICP-AES, thermal ionisation and secondary ion mass spectrometry, as well as neutron activation analysis, X-ray fluorescence and atomic absorption spectrometry. A comprehensive review of the development of reference materials, often essential to these techniques, is also provided. The contributions assembled serve both to keep readers informed of advances they may be unfamiliar with, but also as a means of showcasing examples of the breadth and depth of work being conducted in these fields.     

Geomorphological findings on the build-up of pleistocene glaciation in Southern Tibet and on the problem of inland ice —

Summary The last Ice Age (Würm) glacier cover was reconstructed on the basis of standard geomorphological indicators in S Tibet between the S slope and N slope of the Himalaya by way of the Tibetan Himalaya to the Transhimalaya (28° – 29° 50' N/85° 40' – 91° 10' E). At the same time, though subject to varying density of data, the process of Late and Post-Glacial deglaciation to Neo-Galacial and Recent glacier cover was considered. Evidence of an almost total glaciation of S Tibet was found in indicators like glaciated knobs, trough valleys with pronounced flank polishings and limits of glacial scouring on nunataks, as well as in findings of erratics, lateral moraines, end moraines, and terraces of outwash plains. This total glaciation took the form of an ice-stream network and attained a thickness of at least 1200 m. Ice-free to about 87° – 86° E, the Tsangpo valley with its sander deposits occupied the gap between the glacier areas of the Tibetan and High Himalayas in the S (I 3) and those of the Transhimalaya in the N (I 2). In the light of recently glaciated Late Glacial terminal moraines and ice marginal rapms it has been possible to estimate a glacio-isostatic uplift of c. 400 m during 10 x 10³ years (an average of 40 mm/year) following deglaciation. It is about 3 to 8 times greater than the tectonic uplift of the High Himalaya. The post-glacially intensified uplift of the S Tibetan Plateau by comparison with the High Himalaya is attributed to the much greater glacier burden during the Ice Age.In the area under investigation a High Glacial ELA depression (equilibrium line altitude depr.) of at least 1200 (1180) m was reconstructed for a mean altitude of about 4700 (4716) m asl. Assuming constant hygric conditions and a gradient of 0.7° C/100 m, the temperature drop at the time would have been 8.4° C. Since precipitation during the Ice Age must, if anything, have been less, a drop in summer temperature of about 10° C may be regarded as probable.     

A size classification for debris flows

A 10-fold classification for debris flow size is proposed based on total volume, peak discharge and area inundated by debris. Size classes can be used for regional overview studies where detailed site investigations are either unnecessary, too costly or where the highest hazard and risk creeks need to be identified for further study. They are also useful to compare the regional impact between affected areas and the effects of rainstorms, and they allow lay-people to obtain an understanding of debris flow magnitude and consequences. Finally, different size classes allow the estimation of travel times to points of interest based on empirically derived equations. It is proposed that agencies concerned with debris flows should establish a documentation of debris flow size according to this classification, which serves as a data base for hazard and risk planning.     

The structural vulnerability in the framework of natural hazard risk analyses and the exemplary application for storm loss modelling in Tyrol (Austria)

In the context of natural hazard-related risk analyses, different concepts and comprehensions of the term risk exist. These differences are mostly subjected to the perceptions and historical backgrounds of the different scientific disciplines and results in a multitude of methodological concepts to analyse risk. The target-oriented selection and application of these concepts depend on the specific research object which is generally closely connected to the stakeholders’ interests. An obvious characteristic of the different conceptualizations is the immanent various comprehensions of vulnerability. As risk analyses from a natural scientific-technical background aim at estimating potential expositions and consequences of natural hazard events, the results can provide an appropriate decision basis for risk management strategies. Thereby, beside the preferably addressed gravitative and hydrological hazards, seismo-tectonical and especially meteorological hazard processes have been rarely considered within multi-risk analyses in an Alpine context. Hence, their comparative grading in an overall context of natural hazard risks is not quantitatively possible. The present paper focuses on both (1) the different concepts of the natural hazard risk and especially their specific expressions in the context of vulnerability and (2) the exemplary application of the natural scientific-technical risk concepts to analyse potential extreme storm losses in the Austrian Province of Tyrol. Following the corresponding general risk concept, the case study first defines the hazard potential, second estimates the exposures and damage potentials on the basis of an existing database of the stock of elements and values, and third analyses the so-called Extreme Scenario Losses (ESL) considering the structural vulnerability of the potentially affected elements at risk. Thereby, it can be shown that extreme storm events can induce losses solely to buildings and inventory in the range of EUR 100–150 million in Tyrol. However, in an overall context of potential extreme natural hazard events, the storm risk can be classified with a moderate risk potential in this province.     

Pleistocene/Holocene climate change, re-establishment of fluvial drainage network and increase in relief in the Swiss Alps

ABSTRACT Data are presented about modern sediment discharge of the Swiss rivers and related to the size of catchments. The information reveals that the Central Alps have experienced denudation rates of ≈0.15 mm yr⁻¹ in the foreland, and ≈0.5 mm yr⁻¹ in the Alpine core. Mapping, however, indicates that modern erosion only affects 30–50% of the Alpine surface, and that fluvial and associated hillslope processes have focused erosion in 50–200-m-deep valleys. These valleys are incised into the glacial surface. If this limited spatial extent of erosion is considered, then effective erosion rates are significantly higher than average denudation rates. These effective rates equal or locally exceed modern rates of rock uplift. This implies that the modification of erosional processes related to the Pleistocene/Holocene climate change has resulted in an increase in the relief at a local scale. At a drainage basin scale, however, the relief appears not to change at present.