GNGTS 2019 - Atti del 38° Convegno Nazionale

GNGTS 2019 S essione 3.2 655 followed and correlated between adjacent profiles. The ice bottom appeared as a discontinuous reflecting horizon in all the surveys. A low-amplitude reflector deeper than the ice bottom was depicted in a few profiles (Fig. 2b). This interface is characterized by a steeper dipping with respect to the ice bottom, in dip direction opposite to the glacier movement, reaching times higher than 1150 ns (depth>100 m) in the center of the profile, at a distance of approximately 120 m from the glacier front. Despite the dense GPR survey distribution, the ice bottom surface was detected only in radargrams acquired on the frontal lobes, while noisy and uninterpretable results were obtained upstream. Glacier bottommanual picks were interpolated to reconstruct an ice thickness map (Fig. 2c) that was compared with the previous studies. A traditional U-shaped bottom morphology was reconstructed for the N lobe (Fig. 2d), with considerable ice depths in the axial part (100–110 m) despite the proximity to the terminus. The S lobe is conversely characterized by significantly shallower ice depths and a flatter morphology. Conclusions. Continuous GPR profiling provided denser data coverage with respect to previous local measurements, enabling for a better definition of the ice bottom morphology. Significant ice thickness variations were detected in the upper part of the N lobe, with a transition from convex to concave glacier topography. Below the ice bottom, low-amplitude reflectors having steeper dip were identified only in the frontal portion of the N lobe. These elements may indicate the bedrock presence at a depth of around 80 m from the glacier surface close to the northern terminus and rapidly deepening upstream. Consequently, a thick layer (more than 40 m) of subglacial deposits may be present between ice and bedrock, explaining the differences in ice thickness estimation between the studies of De Visintini (1961) and VAW-ETH (1985). Further glaciological analyses are planned to understand the influence of the glacier subsurface conditions on the measured geophysical data. Future geophysical campaigns on site should be addressed to reach satisfactory imaging of the glacier bottom in the upstream sectors, and to monitor ice thickness variations over the investigated frontal areas. References Binder D., Brückl E., Roch K.H., Behm M., Schöner W. and Hynek B.; 2009: Determination of total ice volume and ice-thickness distribution of two glaciers in the Hohe Tauern Region, Eastern Alps, from GPR data . Ann. Glaciol., 50 , 71–79, DOI 10.3189/172756409789097522. Colombero C., Comina C., De Toma E. and Godio A.; 2019: Ice thickness estimation from geophysical investigations on the terminal lobes of Belvedere Glacier (NW Italian Alps) . Remote Sensing, 11 (7), 805, DOI 10.3390/ rs11070805. De Visintini G.; 1961: Rilievo sismico a riflessione sul Ghiacciaio del Belvedere (Monte Rosa) . Bollettino del Comitato Glaciologico Italiano, Serie II, 10 , 65–70. Kulkarni A., Bahuguna I., Rathore B., Singh S., Randhawa S., Sood R. and Dhar S.; 2007: Glacial retreat in Himalaya using Indian Remote Sensing satellite data . Curr. Sci., 92 , 69–74. Maurer H. and Hauck C.; 2007: Geophysical imaging of Alpine rock glaciers . J. Glaciol., 53 , 110–120, DOI 10.3189/172756507781833893. Merz K., Maurer H., Rabenstein L., Buchli T., Springman S.M. and Zweifel M.; 2016: Multidisciplinary geophysical investigations over an Alpine rock glacier . Geophysics, 81 , WA147–WA157, DOI 10.1190/geo2015-0157.1. Navarro F. and Eisen O.; 2009: Ground-penetrating radar in glaciological applications . Remote Sens. Glaciers, 195–229, DOI 10.1201/b10155-12. Picotti S., Francese R., Giorgi M., Pettenati F. and Carcione J.M.; 2017: Estimation of glacier thicknesses and basal properties using the Horizontal-to-Vertical component Spectral Ratio (HVSR) technique from passive seismic data . J. Glaciol., 63 , 229–248, DOI 10.1017/jog.2016.135. VAW-ETH; 1985: Studi sul comportamento del Ghiacciaio del Belvedere , Macugnaga, Italia. Relazione 97, 3, 76-109. Ye Q., Kang S., Chen F. and Wang J.; 2006: Monitoring glacier variations on Geladandong Mountain, Central Tibetan Plateau, from 1969 to 2002 using Remote-Sensing and GIS technologies . J. Glaciol., 52 , 537–545, DOI 10.3189/172756506781828359.