MULTIDISCIPLINARY INVESTIGATIONS ON THREE ROCK GLACIERS IN THE SWISS ALPS: LEGACIES AND FUTURE PERSPECTIVES

This paper recognizes the contribution of Professor Wilfried Haeberli for his inspiration and leadership in the field of permafrost science and his generous encouragement, both direct and indirect, to the ETH Researchers who have, through him, endeavoured to contribute to this fascinating research area. The multidisciplinary investigations described in this paper have focused on three rock glaciers, Muragl, Murtèl‐Corvatsch and Furggwanghorn, all of which have been subject to a varying degree of prior study, and which are continuing to attract new generations of researchers to understand and explain the processes and predict future behaviour. This paper marks a stage at which it is possible to summarize some advances in the state of the art and associated innovations that can be attributed to early motivation by Wilfried Haeberli and offers a tribute as well as gratitude for his ongoing feedback and advice. Some thoughts on the development of thermokarst due to water ponding and flow, and a conceptual model of geotechnical mechanisms that aim to explain some aspects of rock glacier kinematics, are also introduced.     

Natural Partial Melting of Spinel Lherzolite

Spinel lherzolite nodules from Dreiser Weiher, Germany, containsmall glass bearing microcrystalline blebs that were formedfrom a partial melt. The partial melting occurred during contactanatexis of lherzolite surrounding a deep seated magma chamberin the mantle. The blebs formed from melt drops that were isolatedfrom each other and not from an intergranular film. The resultssuggest that primary magma originates as small melt drops ina lherzolitic matrix. This evidence indicates a limited mobilityof traces of partial melt in the mantle, and suggests that theaccumulation of primary magmas formed at very small degreesof partial melting is unlikely.     

The Wilhelmøya Formation (Upper Triassic-Lower Jurassic) at Bohemanflya, Spitsbergen

An 18.5 m thick shale sequence of Norian-Rhaetian age is described from the Bohemanfiya-Syltoppen area (north of Isfjorden, central Spitsbergen). Lithological, petrographical and palynological analyses show that the sequence represents a marginal development of the lower part of the Wilhelmeya Formation. The depositional history at the Triassic-Jurassic transition is discussed in the light of this new evidence. The Wilhelmøya Formation was probably deposited during a weak marine transgression over an area of low relief. Low sediment supply and current and wave reworking of the sediments characterized the depositional conditions.     

PRINCIPLES OF DIGITAL WIENER FILTERING*

The theory of statistical communication provides an invaluable framework within which it is possible to formulate design criteria and actually obtain solutions for digital filters. These are then applicable in a wide range of geophysical problems. The basic model for the filtering process considered here consists of an input signal, a desired output signal, and an actual output signal. If one minimizes the energy or power existing in the difference between desired and actual filter outputs, it becomes possible to solve for the so-called optimum, or least squares filter, commonly known as the “Wiener” filter. In this paper we derive from basic principles the theory leading to such filters. The analysis is carried out in the time domain in discrete form. We propose a model of a seismic trace in terms of a statistical communication system. This model trace is the sum of a signal time series plus a noise time series. If we assume that estimates of the signal shape and of the noise autocorrelation are available, we may calculate Wiener filters which will attenuate the noise and sharpen the signal. The net result of these operations can then in general be expected to increase seismic resolution. We show a few numerical examples to illustrate the model's applicability to situations one might find in practice.     

Holocene millennial to centennial carbonate cyclicity recorded in slope sediments of the Great Bahama Bank and its climatic implications

A 38 m long sediment core (MD992201) retrieved from a water depth of 290 m from the leeward margin of the Great Bahama Bank (GBB; 25°53·49′N, 79°16·34′W) has been investigated for changes in aragonite content. The core covers the Mid to Late Holocene (the past 7230 yr). Sediment lightness (L*-values) was used as a proxy for aragonite content, based on a high linear correlation (R = 0·93) between the X-ray diffraction derived aragonite content and L*-values. The resulting time resolution of the L*-values derived aragonite content ranges from 1 yr at the base of the core to 4 yr at the top. Detailed time series analysis using Monte Carlo Singular Spectrum Analysis and spectral analysis (Lomb–Scargle Fourier transform) identifies the presence of seven signals with varying amplitudes and wavelengths that could be traced throughout the past 5500 yr. During the first ∼1600 yr of sedimentation the aragonite record is dominated by the initial flooding of the flat-topped GBB. Superimposed on a multimillennial signal, related to Holocene sea-level changes, a millennial-scale fluctuation and five quasi-periodic oscillations were detected (∼1·3–2 kyr, ∼500–600 yr, ∼380 yr, ∼260 yr, ∼200 yr and ∼100 yr period). Comparisons with other proxies (e.g. tree ring-Δ¹⁴C, ¹⁰Be and δ¹⁸O in ice cores) provides information on the origin and dynamics of the individual signals. The analysis shows that the ∼200 yr and ∼100 yr signals can be attributed to solar forcing. The ∼260 yr, ∼380 yr and the ∼500–600 yr quasi-periodic signals are found to be of climatic origin, whereas the millennial scale fluctuations remain enigmatic, although solar forcing mechanisms seem likely. The data show that variability of solar output as well as past oceanographic and atmospheric changes have modulated the Mid to Late Holocene climate, which in turn controlled sediment input variations found in the Holocene wedge leeward of the GBB. Although these periplatform sediments have a rather uniform appearance, they still contain a large variety of subtle sedimentary variations.     

The Trachybasaltic Suite of Jan Mayen

The alkalic suite of Jan Mayen is of the trachybasaltic typewith a K₂O/Na₂O ratio of about 1·64. The suite includesall intermediate types of lavas between ankaramite and trachyte,with ankaramites being particularly prevalent. The major andtrace element trends are well defined. A new method allows distinctionbetween fractionated and accumulative ankaramites, and it isshown that the most primitive ankaramite contains 13–14per cent MgO. Experimentally determined P-T phase relationsof this composition suggest that it might be a primary composition,formed by partial melting of a spinel lherzolitic source at19·5kb and 1415°C. The fractionation from ankaramiteto trachybasalt occurred at low pressure, and was controlledby delayed gravitative settling of phenocrysts, while the fractionationfrom trachybasalt to trachyte is explained by crystallizationon the walls of the magma chambers.     

Improved sampling of soft bottom sediments by combined box and piston coring

Field tests demonstrate that sampling of soft bottom sediments can be significantly improved by combined box coring and shipboard sampling using hand-operated piston coring. A convenient piston equipment devised for such subsampling is presented.