Calculation and visualisation of future glacier extent in the Swiss Alps by means of hypsographic modelling

The observed rapid glacier wastage in the European Alps during the past 20 years already has strong impacts on the natural environment (rock fall, lake formation) as well as on human activities (tourism, hydro-power production, etc.) and poses several new challenges also for glacier monitoring. With a further increase of global mean temperature in the future, it is likely that Alpine glaciers and the high-mountain environment as an entire system will further develop into a state of imbalance. Hence, the assessment of future glacier geometries is a valuable prerequisite for various impact studies. In order to calculate and visualize in a consistent manner future glacier extent for a large number of individual glaciers (> 100) according to a given climate change scenario, we have developed an automated and simple but robust approach that is based on an empirical relationship between glacier size and the steady-state accumulation area ratio (AAR₀) in the Alps. The model requires digital glacier outlines and a digital elevation model (DEM) only and calculates new glacier geometries from a given shift of the steady-state equilibrium line altitude (ELA₀) by means of hypsographic modelling. We have calculated changes in number, area and volume for 3062 individual glacier units in Switzerland and applied six step changes in ELA₀ (from + 100 to + 600 m) combined with four different values of the AAR₀ (0.5, 0.6, 0.67, 0.75). For an AAR₀ of 0.6 and an ELA₀ rise of 200 m (400 m) we calculate a total area loss of − 54% (− 80%) and a corresponding volume loss of − 50% (− 78%) compared to the 1973 glacier extent. In combination with a geocoded satellite image, the future glacier outlines are also used for automated rendering of perspective visualisations. This is a very attractive tool for communicating research results to the general public. Our study is illustrated for a test site in the Upper Engadine (Switzerland), where landscape changes above timberline play an important role for the local economy. The model is seen as a first-step approach, where several parts can be (and should be) further developed.     

The early interaction between the Caribbean Plateau and the NW South American Plate

The determination of accurate and precise ages for the timing of collision between oceanic plateaus and continental crust requires an understanding of how the indenting and buttressing plates respond to the collision. We present geochronological, thermochronological, geochemical and isotopic analyses of magmatic rocks from the Ecuadorian Andes, which relate to the collision of the Late Cretaceous Caribbean Plateau and Great Arc sequence with NW South America. The cessation of subduction magmatism during 65–64 Ma beneath the eastern edge of Caribbean Plateau was synchronous with accelerated surface uplift and exhumation within the buttressing continental margin during 75–65 Ma. We interpret this as the collision of the leading edge of the Caribbean Plateau and arc sequence with the South American Plate at 75–65 Ma. A U/Pb (zircon) SHRIMP age of 87.10 ± 1.66 (2σ) Ma, yielded by an accreted fragment of the plateau, precludes previous estimates of collision at 85–80 Ma if the plateau erupted above the Galápagos hotspot. Terra Nova, 18, 264–269, 2006     

Paleo-bathymetry of the northern North Atlantic and consequences for the opening of the Fram Strait

In the past decade, the geophysical database in the northern North Atlantic and central Arctic Ocean constantly grew. Though far from being complete, the information from new aeromagnetic and seismic data north of the Jan Mayen Fracture Zone and in the Arctic Ocean, in combination with existing compiled geological and geophysical data, is used to produce paleo-bathymetric maps for several Cenozoic time intervals. This paleo-bathymetric model provides evidence for an initial deep-water exchange through the Fram Strait starting around 17 Ma. Furthermore, the model suggests that crustal rifting prior to initial seafloor spreading might have facilitated an earlier deep-water connection. This confirms that the paleo-topography of the Yermak Plateau played an important role in allowing at least the exchange of shallow water between the northern North Atlantic and the Arctic Ocean before the opening of the deep-water Fram Strait gateway. In the south of the research area the paleo-bathymetric model indicates that the first possibility for a deep-water overflow from the Norwegian-Greenland Sea to the North Atlantic could have been between 15 and 20 Ma.     

Control factors on turbidite sedimentation in a deep-sea trench setting. – The example of the Schlieren Flysch (Upper Maastrichtian-Lower Eocene,Central Switzerland)

Abstract

Deep-sea turbidite sedimentation in convergent margin settings generally is controlled by tectonic uplift, climate and eustatic sea-level variations. The rate of tectonic uplift governs the relief of the source area and the position of the base level (coinciding with sea-level), climate influences the rate and style of weathering and continental runoff and eustatic seal-level additionally shifts the base level, functioning with the concurrently working tectonic movements. Thus, these factors primarly determine the availability of sediment (yield and nature of material and the site of intermittent storage) at the basin margin which is unlocked periodically to flow downslope to the basin.

This paper attempts to decipher quantitatively the importance of the individual factors in the Late Maastrichtian to Early Eocene Schieren Flysch Croup. The flysch was deposited in a moderately converging remnant oceanic trench basin. Mean parameters are calculated on the basis of formations and the duration of nannofossil zones comprised in. For transposing these zone into absolute age intervals the problem of inconsistent durations in current time scales had to be solved by a best-fit approach. Frequencies and periodicities of turbidite events, decompacted and compacted sedimentation rates (the latter are considered as apparent denudation rates) are calculated to reveal the dynamics of sedimentation. Climatic evidence is deduced from clay mineralogy. Changing uplift rates in the drainage area are indirectly interpreted from back-stripped tectonic subsisdence rates in the basin.

The obtained data point to an immediate control of sub-duction-Iinked tectonic uplift in the bordering drainage and shelf area on turbidite sedimentation, as frequency and thickness of the turbidite events are closely correlated with the increasing tectonic subsisdence in the basin (assumed to match the rate of subduction and underplating). This general trend is modified by the temporary migration of the oceanic hinge zone towards the trench causing periodically the starvation of outer portions of the basin at the transition from Early to Late Paleocene and Late Paleocene to Eocene. Regional climatic trends additionnaly rule the turbidite facies development and apparent denudation rates. In the upper part of Early Eocene series high rate mud dominated sediments correlate with warm/humid conditions and in Late Paleocene deposits low rate sandy sediments coincide with cool ones. During the Late Paleocene period the global 2nd-order sea-level lowering probably may be responsible for the by-passing of the shelf by the coarse grained sediments.     

Preserved landscapes underneath the Antarctic Ice Sheet reveal the geomorphological history of Jutulstraumen Basin

The landscape of Antarctica, hidden beneath kilometre-thick ice in most places, has been shaped by the interactions between tectonic and erosional processes. The flow dynamics of the thick ice cover deepened pre-formed topographic depressions by glacial erosion, but also preserved the subglacial landscapes in regions with moderate to slow ice flow. Mapping the spatial variability of these structures provides the basis for reconstruction of the evolution of subglacial morphology. This study focuses on the Jutulstraumen Glacier drainage system in Dronning Maud Land, East Antarctica. The Jutulstraumen Glacier reaches the ocean via the Jutulstraumen Graben, which is the only significant passage for draining the East Antarctic Ice Sheet through the western part of the Dronning Maud Land mountain chain. We acquired new bed topography data during an airborne radar campaign in the region upstream of the Jutulstraumen Graben to characterise the source area of the glacier. The new data show a deep relief to be generally under-represented in available bed topography compilations. Our analysis of the bed topography, valley characteristics and bed roughness leads to the conclusion that much more of the alpine landscape that would have formed prior to the Antarctic Ice Sheet is preserved than previously anticipated. We identify an active and deeply eroded U-shaped valley network next to largely preserved passive fluvial and glacial modified landscapes. Based on the landscape classification, we reconstruct the temporal sequence by which ice flow modified the topography since the beginning of the glaciation of Antarctica.