Renato R. Colucci

Late Holocene evolution of glaciers in the southeastern Alps

ABSTRACT The Julian Alps (in the southeastern European Alps, Italy and Slovenia) represent an important case study area for the study of small and very small maritime glaciers. High mean annual precipitation results in great snow accumulation during the winter, permitting the presence of ice bodies with the lowest Equilibrium Line Altitudes in the Alps. During the Little Ice Age (LIA) 19 small glaciers (<1 km2) existed, covering a total area of 2.4 km2. By 2012, the glacierized area had shrunk by 84% and only isolated glacierets and ice patches survived, each having a total area less than 0.5 km2. We present here a geomorphological and palaeoglaciological map of 8 sections of the Julian Alps related to the late Holocene distribution of glaciers, at a scale of 1:6000. Glacier topography during the LIA maximum was reconstructed on the basis of well-expressed geomorphological features together with historical archive data. The present-day distribution of ice bodies was inferred from orthophotos and 1 m resolution digital terrain models derived from airborne laser scanning. The past and present areal extent and surface morphology of glaciers permits calculation of volume loss since the LIA, which is estimated at 96%.

Unprecedented heat wave in December 2015 and potential for winter glacier ablation in the eastern Alps

We document the occurrence in December 2015 of unprecedented high monthly mean temperatures in the observational record of mountain sites in the eastern Alps. For the first time in the last 150 years mean December temperature exceeded 0 °C at elevations between 2100 and 2500 m, with December mean anomalies exceeding 6.5 °C with respect to the 1971–2000 mean. Along with the absence of snow cover, such temperatures might have lead to unprecedented winter ablation of glaciers in this elevation range. Smaller temperature anomalies occurred in surrounding low elevation sites, highlighting the key role of topography in this event. Specifically, strong inversions associated with the very stable synoptic conditions during the month amplified the anomalies at the high elevations of the mountain glacier sites. We analyze the processes underlying this exceptional event and place this anomaly within the context of future warming scenarios over the region.

Automated reflection picking and inversion: Application to ground and airborne GPR surveys

We apply an automated picking and inversion algorithm to ground-based and airborne glaciological GPR surveys, in order to recover the internal stratigraphy, density distribution, and water content of alpine glaciers. Current glacier monitoring techniques encompass topographic mapping, direct measurements, and GPR surveys. However, the resulting models strongly depend on the assumptions made about the glaciers internal EM velocity and density distributions, which are usually set either constant or slow-varying, with the only constraints given by locally sampled values. Our inversion procedure uses amplitudes and timespace positions of the recorded reflections to recover the EM velocity and thickness of each layer by reconstructing the travel path of each reflected wavelet. The internal density distribution of glaciers is then recovered using well-known empirical formulas. The input reflections are automatically picked using an algorithm designed to detect and track any recorded event characterized by lateral phase continuity. Such a procedure is mostly independent of the interpreter and only requires a few input parameters and thresholds. High data densities lead to accurate and statistically sound models, while 4-D GPR surveys allow monitoring of the temporal variations of a glacier and the estimation of its mass balance.

Interplay of grounding-line dynamics and sub-shelf melting during retreat of the Bjørnøyrenna Ice Stream

The Barents Sea Ice Sheet was a marine-based ice sheet, i.e., it rested on the Barents Sea floor during the Last Glacial Maximum (21 ky BP). The Bjørnøyrenna Ice Stream was the largest ice stream draining the Barents Sea Ice Sheet and is regarded as an analogue for contemporary ice streams in West Antarctica. Here, the retreat of the Bjørnøyrenna Ice Stream is simulated by means of two numerical ice sheet models and results assessed against geological data. We investigate the sensitivity of the ice stream to changes in ocean temperature and the impact of grounding-line physics on ice stream retreat. Our results suggest that the role played by sub-shelf melting depends on how the grounding-line physics is represented in the models. When an analytic constraint on the ice flux across the grounding line is applied, the retreat of Bjørnøyrenna Ice Stream is primarily driven by internal ice dynamics rather than by oceanic forcing. This suggests that implementations of grounding-line physics need to be carefully assessed when evaluating and predicting the response of contemporary marine-based ice sheets and individual ice streams to ongoing and future ocean warming.

Ice Caves in Italy

Abstract In Italy, more than 1600 caves are classified as cryo-caves, due to the presence of multiyear snow, firn, or ice. Previous regional studies show that at least 10% of such caves can be included in the ice cave classification, because they have a perennial ice deposit. However, the strong differences in the karstological characteristics of the Italian geology allows having not only caves formed in limestone, dolomite, or marble terrains, in the Alps as well as in the Apennines, but also in lava tubes on the Etna Volcano. Four ice caves are reported here as examples of three different mechanisms of ice cave formation and evolution. From Grigna Settentrionale, central Alps, a vertical shaft ice deposit mainly formed by dripping water was studied by chemical and stable isotope record. Two high altitude ice caves originated by snow accumulation and ice dipping were studied in the Canin massif, southeastern Alps, and a lava tube from Etna volcano was studied for its ice dynamics and air-circulation mechanisms. These four examples provide important data on the evolution of such ice deposits, giving a first clue on their progressive reduction under recent climate forcing.