Article

Isostatic rebound following the Alpine deglaciation: Impact on the sea level variations and vertical movements in the Mediterranean region

Geophysical Journal International (Impact Factor: 2.72). 06/2005; 162(1):137 - 147. DOI: 10.1111/j.1365-246X.2005.02653.x

ABSTRACT The present-day sea level variations and geodetically observed ground deformations in the Mediterranean area are normally ascribed to the combined effect of tectonic or human-driven subsidence and postglacial uplift as a result of the melting of the major Pleistocene ice sheets. However, another potential cause of deformation, only marginally considered to date, is the melting of the glacier that covered the Alps during the last glacial maximum (LGM). The aim of this paper is to predict the long-term sea level variations induced by the melting of both the late-Pleistocene and Alpine ice sheets and compare our results with the relative sea level (RSL) observations available in the Mediterranean region. This task is accomplished solving the sea level equation (SLE) for a spherically symmetric viscoelastic Earth. Our analysis shows that the melting of the Alpine glacier has marginally affected the Holocene sea level variations in the near-field sites in southern France (Marseilles and Roussillon) and the central Tyrrhenian sea (Civitavecchia), and that the RSL predictions are significantly sensitive to the chronology of the remote ice aggregates. The computations, which are performed using a specific mantle viscosity profile consistent with global observations of RSL rise, show that the uplift rate driven by the Alpine isostatic readjustment may account for up to of the rates observed at GPS stations in the western portion of the chain. Our results suggest that a thorough modelization of both near- and far-field ice sheets is necessary to gain a better insight into the present-day deformations and sea level variations in the Mediterranean region.

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    • "Active tectonics thus seem to be dominated by isostasy/buoyancy forces rather then shortening along the Alpine Europe/Adria collision zone (e.g., Selverstone, 2005; Sue et al., 2007, and references therein). Vertical displacements relative to a reference point in Aarburg (Swiss Molasse basin) are ∼0:25–1:5 mm yr −1 (Schaer and Jeanrichard, 1974; Schlatter et al., 2005), in response to the isostatic re-adjustment to erosion (e.g., Champagnac et al., 2007), post-LGM and ongoing ice melting (Stocchi et al., 2005; Barletta et al., 2006), with a possible minor effect of tectonic shortening and/or deep-seated processes such as the detachment of the European slab (Calais et al., 2002; Lippitsch et al., 2003). The relative importance of these three components in determining measured rock uplift rates, however, is still debated (e.g., Champagnac et al., 2009). "
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    ABSTRACT: The present-day topography of the European Alps shows evidence of intense glacial reshaping. However, significant questions regarding Alpine landscape evolution during glaciations still persist. For example, large-scale topographic analyses suggest that glacial erosion is maximized at and above the glaciers’ long-term Equilibrium Line Altitude. In contrast, measurements of long-term denudation rates from low temperature thermochronology suggest high erosion towards low altitudes, leading to an increase of local relief in response to glacial erosion. Based on sediment record, low-temperature thermochronology and burial cosmogenic nuclide dating, it has also been proposed that the mid-Pleistocene climatic transition from symmetric, 40kyr to asymmetric, 100kyr glacial/interglacial oscillations sets the onset of intense glacial erosion within the Alps. However, this climate threshold in glacial erosion has not been showed in other orogens, and positive feedbacks between climate periodicity and glacial erosion efficiency still remain to be proven. We focus on the Rhône valley (Swiss Alps), and use a numerical model to estimate patterns and magnitudes of glacial erosion. Comparing modeling results on an advanced reconstruction of the pre-glacial topography (Sternai et al., 2012) and the present-day landforms, we found that erosion propagates headward as the landscape evolves from a fluvial to a glacial state, leading to an initial increase of local relief in the major valley trunk followed by subsequent erosion at high elevations. We also test the mid-Pleistocene transition hypothesis by running a 2Myr numerical experiment including a shift from symmetric, 40kyr to asymmetric, 100kyr glacial/interglacial oscillations at 1Myr. Although the change of climate periodicity may have produced an intensification of glacial erosion, our results suggest that other factors such as an increase of rock uplift and/or progressive climate cooling are required to explain enhanced valley carving at approximately 1Myr.
    EGU; 04/2014
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    • "average erosion. However, glacial isostatic rebound models suggest as much as 0.9 mm/yr of uplift in the western Alps due to the glacier shrinkage after the Little Ice Age (Barletta et al., 2006) and as much as 0.3 mm/yr of uplift due to the Last Glacial Maximum (Stocchi et al., 2005). Therefore, the geodetic vertical velocities could be the sum of these three processes . "
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    ABSTRACT: Mechanisms that control seismic activity in low strain rate areas such as western Europe remain poorly understood. For example, in spite of low shortening rates of <0.5 mm/yr, the Western Alps and the Pyrenees are underlain by moderate but frequent seismicity detectable by instruments. Beneath the elevated part of these mountain ranges, analysis of earthquake focal mechanisms indicates extension, which is commonly interpreted as the result of gravitational collapse. Here we show that erosional processes are the predominant control on present-day deformation and seismicity. We demonstrate, using finite element modeling, that erosion induces extension and rock uplift of the elevated region of mountain ranges accommodating relatively low overall convergence. Our results suggest that an erosion rate of ∼1 mm/yr can lead to extension in mountain ranges accommodating significant shortening of <3 mm/yr. Based on this study, the seismotectonic framework and seismic hazard assessment for low strain rate areas need to be revisited, because erosion-related earthquakes could increase seismic hazard. Previous Section Next Section
    Geology 04/2013; 41(4):467-470. DOI:10.1130/G33942.1 · 4.64 Impact Factor
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    • "Active tectonics thus seem to be dominated by isostasy/buoyancy forces rather then shortening along the Alpine Europe/Adria collision zone (e.g., Selverstone, 2005; Sue et al., 2007, and references therein). Vertical displacements relative to a reference point in Aarburg (Swiss Molasse basin) are ∼0:25–1:5 mm yr −1 (Schaer and Jeanrichard, 1974; Schlatter et al., 2005), in response to the isostatic re-adjustment to erosion (e.g., Champagnac et al., 2007), post-LGM and ongoing ice melting (Stocchi et al., 2005; Barletta et al., 2006), with a possible minor effect of tectonic shortening and/or deep-seated processes such as the detachment of the European slab (Calais et al., 2002; Lippitsch et al., 2003). The relative importance of these three components in determining measured rock uplift rates, however, is still debated (e.g., Champagnac et al., 2009). "
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    ABSTRACT: The present-day topography of the European Alps shows evidence of intense glacial reshaping. However, significant questions regarding Alpine landscape evolution during glaciations still persist. In this study, we focus on the Rhône valley (Swiss Alps), and use a numerical model to estimate patterns and magnitudes of glacial erosion. Comparing modeling results on a reconstructed pre-glacial topography and the present-day landforms, we find that the landscape response to glaciation is more complex than a simple “buzzsaw” mechanism (by which glacial erosion sets the height of mountain ranges) or increase of relief due to localized valley incision. Instead, glacial erosion propagates headward as the landforms evolve from a fluvial to a glacial state, leading to an initial increase of local relief followed by subsequent erosion at high elevations. It has also been proposed that the mid-Pleistocene climatic transition of glacial/interglacial oscillations from periods of 40 kyr (with symmetric shapes) to periods of 100 kyr (with asymmetric shapes) promoted glacial erosion within the Alps. Although this change of climate periodicity may have contributed to enhance glacial erosion, our results suggest that other factors such as an increase in rock uplift and/or progressive climate cooling are required to explain enhanced glacial carving at ∼1Ma.
    Earth and Planetary Science Letters 04/2013; 368:119–131. DOI:10.1016/j.epsl.2013.02.039 · 4.72 Impact Factor
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