The use of GPS for marine positioning in Germany—requirements,experience, and concepts

Abstract

While beginning to establish a German Civil GPS Information and Observation Service in 1990, the actual and (near) future GPS market in Germany was analyzed. In addition, the feasibility of using GPS for water authority tasks has been studied during past years. Typical capabilities in this area are real‐time positioning for hydrographic surveying (kinematic application) and precise transfer of levels to tide gauges and verification at offshore positions.

The article describes the user interests, the requirements, some of the test campaigns, and the derived concepts for future applications.     

Numerical simulations of microstructures using the <Emphasis Type="Italic">Elle</Emphasis> platform: A modern research and teaching tool

The last 20 years have seen a manifold increase in the application of numerical simulations in the earth sciences. This contribution aims to provide an overview of the possibilities of using numerical techniques, in particular the numerical simulation package Elle, as an aid in the training for microstructural interpretation in rocks. Three sets of experiments are described to illustrate the range of simulations currently possible, investigating the effects of grain growth, polyphase deformation and dynamic recrystallisation. Numerical simulations of static annealing of a pre-deformed natural sample show that Crystallographic Preferred Orientations can still be used for the interpretation of kinematic and deformation conditions, even after substantial postdeformational annealing. However, the grain network characteristics such as grain size, grain size distribution, boundary shapes and aspect ratios are rapidly altered during annealing, especially if the grains possessed highly contrasting internal strain energies.     

Formation of pyroxenite layers in the Totalp ultramafic massif (Swiss Alps) - Insights from highly siderophile elements and Os isotopes

Pyroxenitic layers are a minor constituent of ultramafic mantle massifs, but are considered important for basalt generation and mantle refertilization. Mafic spinel websterite and garnet-spinel clinopyroxenite layers within Jurassic ocean floor peridotites from the Totalp ultramafic massif (eastern Swiss Alps) were analyzed for their highly siderophile element (HSE) and Os isotope composition.Aluminum-poor pyroxenites (websterites) display chondritic to suprachondritic initial γ_Os (160 Ma) of −2 to +27. Osmium, Ir and Ru abundances are depleted in websterites relative to the associated peridotites and to mantle lherzolites worldwide, but relative abundances (Os/Ir, Ru/Ir) are similar. Conversely, Pt/Ir, Pd/Ir and Re/Ir are elevated.Aluminum-rich pyroxenites (clinopyroxenites) are characterized by highly radiogenic ¹⁸⁷Os/¹⁸⁸Os with initial γ_Os (160 Ma) between +20 and +1700. Their HSE composition is similar to that of basalts, as they are more depleted in Os, Ir and Ru compared to Totalp websterites, along with even higher Pt/Ir, Pd/Ir and Re/Ir. The data are most consistent with multiple episodes of reaction of mafic pyroxenite precursor melts with surrounding peridotites, with the highest degree of interaction recorded in the websterites, which typically occur in direct contact to peridotites. Clinopyroxenites, in contrast, represent melt-dominated systems, which retained the precursor melt characteristics to a large extent. The melts may have been derived from a sublithospheric mantle source with high Pd/Ir, Pt/Ir and Re/Os, coupled with highly radiogenic ¹⁸⁷Os/¹⁸⁸Os compositions. Modeling indicates that partial melting of subducted, old oceanic crust in the asthenosphere could be a possible source for such melts.Pentlandite and godlevskite are identified in both types of pyroxenites as the predominant sulfide minerals and HSE carriers. Heterogeneous HSE abundances within these sulfide grains likely reflect subsolidus processes. In contrast, large grain-to-grain variations, and correlated variations of HSE ratios, indicate chemical disequilibrium under high-temperature conditions. This likely reflects multiple events of melt-rock interaction and sulfide precipitation. Notably, sulfides from the same thick section for the pyroxenites may display both residual-peridotite and melt-like HSE signatures. Because Totalp pyroxenites are enriched in Pt and Re, and depleted in Os, they will develop excess radiogenic ¹⁸⁷Os and ¹⁸⁶Os, compared to ambient mantle. These enrichments, however, do not possess the requisite Pt-Re-Os composition to account for the coupled suprachondritic ¹⁸⁶Os-¹⁸⁷Os signatures observed in some Hawaiian picrites, Gorgona komatiites, or the Siberian plume.     

Out-burst flood (lahar) triggered by retrogressive landsliding, 18 March 2007 at Mt Ruapehu,New Zealand—a successful early warning

The summit crater of Mt Ruapehu volcano normally hosts a 15.4-ha warm lake, whose water has been repeatedly wholly or partly ejected by explosive and extrusive eruptions. Some of the larger eruptions have modified the lake outlet by burying it under unconsolidated tephra (volcanic ash and blocks), creating a dam-break flood hazard independently of the occurrence of an eruption. Eruptions in 1995 and 1996 followed this sequence; a break-out flood was anticipated and a warning system was installed to mitigate the risk from this event and subsequent lahars in the same catchment. The 11-year filling time allowed much planning and rehearsal. The warning system involved manual inspections of dam integrity, and seepage and lake-level monitoring to constrain the likely failure window, and telemetered instruments including a tripwire and geophones to detect breaching of the dam and propagation of the outbreak flood. The dam-collapse sequence, captured by a time-lapse camera, involved a series of retrogressing landslides initiated and accelerated by seepage forces and toe scour when the lake was 1.1 m below overtopping. The barrier failed in two phases on 18th March, 2007, beginning at 09:55 (NZST), with rapid retreat of one of the erosion scarps on the downstream slope of the eastern barrier, initiated by internal erosion. Headward retrogression of the scarp into the barrier formed an initial breach in the dam, after which increasing outflow led to erosion and undercutting of the wider downstream toe of the western barrier. A final, larger dam breach occurred between 11:21 and 11:22 as slope instability caused retrogressive failure of the remaining barrier. Five-hundred meters downstream of the dam, a large landslide was reactivated by toe scour during the flood, contributing about a million cubic meters of solid material to the volumetric bulking of the outflow, which reached the coast, 215 km away, 17 h later. The success of the planning and warning system allowed the whole event to occur with little damage to infrastructure and without causing injury.