Glacio–isostatic Adjustment in the Po Plain and in the Northern Adriatic Region

Abstract

Vertical movements in the Po plain (northern Italy) are controlled by natural and anthropogenic effects. Since Italy is located in the far-field of the former late Pleistocene ice sheets, isostatic deformations are primarily driven by melt water loading and represent a major component of long-term natural movements across the entire Mediterranean. In addition to far-field sources, here we consider the isostatic effects of melting of the nearby Würm Alpine ice-sheet, suggesting that it is possible to put bounds on its maximum thickness, extent and chronology by Holocene relative sea level observations from the northern Adriatic. Using various plausible ice models, and adopting a viscosity profile that matches Holocene relative sea level observations in the Mediterranean, we find that melting of the Alpine ice sheet is always responsible for upward movements in the Po plain, currently at rates of * 0.5 mm/yr. When both far-and near-field sources are considered, the rate of sea level change in the Venetian Lagoon for the most reasonable mantle rheology and melting chronology is negative, i.e., opposite to that attributed to human activity and recent climatic variations. However, its amplitude (fractions of mm/yr) is small compared to the secular signal observed by tide gauges (*2 mm/yr), which makes glacial isostasy a second-order mechanism of sea level variation in this region.

Present-day uplift of the European Alps: Evaluating mechanisms and models of their relative contributions

“…According to Norton and Hampel (2010) post-LGM unloading may result in uplift rates > 10 mm/a during the early stages of the deglaciation (i.e.~20-15 ka), but such values quickly reduce to 0.3-0.4 mm/a after~13 ka, when the viscous deformation becomes dominant with respect to the elastic strain. Slightly lower, but similar values were obtained by Stocchi et al (2005) and Spada et al (2009) based on the sea-level equation approach (Farrell and Clark, 1976). Spada et al (2009), in particular, estimate up to~0.5 mm/a of nearpresent uplift rates due to the deglaciation since the LGM and the melting of the remote ice-sheets in the far-field of the Mediterranean based on the ICE-5G model of Peltier (2004) (Fig.…”

“…Slightly lower, but similar values were obtained by Stocchi et al (2005) and Spada et al (2009) based on the sea-level equation approach (Farrell and Clark, 1976). Spada et al (2009), in particular, estimate up to~0.5 mm/a of nearpresent uplift rates due to the deglaciation since the LGM and the melting of the remote ice-sheets in the far-field of the Mediterranean based on the ICE-5G model of Peltier (2004) (Fig. S2).…”

“…In a and c, isolines are shown at 1 mm/a intervals. Note that, since the models proposed by Spada et al (2009) and Mey et al (2016) only address uplift due to the deglaciation, the comparisons in a and c are meaningful only within the Alpine domain. In b and d, the solid line shows mean values, the shaded region shows minimum and maximum values.…”

A benchmark study for glacial isostatic adjustment codes

“…TABOO) to validate numerical codes (and vice versa), especially in the case of computation of short-wavelength (or longtime) limits. The challenging issue of the computation of very large degree Love numbers is not addressed in this study, but would deserve an in-depth analysis due to its relevance in regional investigations of glacio-isostasy Spada et al 2009). Recently, Spada et al (2010) have shown that ALMA provides reliable results up to n = O(10 4 ), which however are still awaiting for a validation by means of a code based on the VNM method (TABOO fails for very large n values, see Spada 2008) or on FE.…”

New insights into active tectonics and seismogenic potential of the Italian Southern Alps from vertical geodetic velocities

“…Proposed mechanisms of uplift include the isostatic response to the last deglaciation, long-term erosion, detachment of the Western Alpine slab, as well as lithospheric and surface deflection due to sub-Alpine asthenospheric convection (Serpelloni et al, 2013;Nocquet et al, 2016). In the study area the isostatic response to last deglaciation and long-term erosion are characterized by longwavelength sub-mm/a patterns (e.g., Sternai et al 2012;Serpelloni et al, 2013), whereas the elastic response to present deglaciation (Barletta et al, 2006;Spada et al, 2009) shows localized peaks of uplift (up to the mm/a scale) far from the study area. In the Eastern Alps, active shortening contributes to the observed uplift, but the pattern and amount of tectonic uplift due to elastic strain accumulation at faults is still unknown.…”