Six Decades (1958–2018) of Geodetic Glacier Mass Balance in Monte San Lorenzo, Patagonian Andes

Daniel Falaschi,María Gabriela Lenzano,Andrés Lo Vecchio,Tobias Bolch,Andrés Rivera,Ricardo Villalba

doi:10.3389/feart.2019.00326

Abstract

A full understanding of glacier changes in the Patagonian Andes over decadal to century time-scales is presently limited by a lack of detailed and appropriate long-term observations. Here, we present geodetic mass and area changes of three valley glaciers from Monte San Lorenzo derived from stereo aerial photos, the Shuttle Radar Topography Mission (SRTM) and satellite imagery (SPOT5 and Pleiades) spanning four periods from 1958 to 2018. Our results indicate that net mass balance was negative throughout the six decades, with a mean mass loss of -1.35 ±0.08 m w.e. a-1 and a total glacier area loss of 14.2 ±0.7 km2 (23 ±1 % or 0.40 ±0.02 % a-1). The period 1981-2000 had the most negative mass budget, with an area-averaged mass loss of 1.67 ±0.11 m w.e. a-1 and a maximum loss of -2.23 ±0.07 m w.e.a−1 at San Lorenzo Sur glacier. Over the periods of 2000-2012 and 2012-2018, the mass budget of these three glaciers remained virtually unchanged at -1.37 ±0.06 m w.e. a-1 and –1.36 ±0.17 m w.e. a-1, respectively. To place these results into a broader geographical context, the mass balance of a further 15 glaciers from around the Monte San Lorenzo massif was determined from 2000 onwards. This wider analysis reveals a period of reduced mass loss of -0.13 ±0.21 m w.e.a−1 from 2012 to 2018 after a period of enhanced mass loss of -0.31 ±0.16 m w.e.a−1 between 2000 and 2012. We find that increasing air temperatures coupled with diminishing precipitation across the region explains the observed patterns and are the main drivers of the negative mass budget. Furthermore, increased calving and melting into recently formed proglacial lakes has further enhanced mass loss at some lake-terminating glaciers.

Highlights

A sustained trend of rapid glacier retreat and depletion has been observed in most mountain and cold regions around the Globe (Zemp et al, 2019) including the Patagonian Andes (Davies and Glasser, 2012; Paul and Mölg, 2014; Masiokas et al, 2015; Falaschi et al, 2017; Dussaillant et al, 2019)
In addition to the increasingly larger area covered by debris, we suggest that after an initial period of relatively high thinning and mass loss at lower elevations (Figures 10d,e), Río Oro glacier is rapidly adjusting to presentday climate conditions and thinning rates are largely independent from glacier-lake interactions
We have determined glacier elevation changes and derived a geodetic mass balance of three valley glaciers in the San Lorenzo massif in the Patagonian Andes by differencing digital elevation models (DEMs) from aerial images, SPOT5 and Pleiades satellite images and the SRTMX band

Summary

Introduction

A sustained trend of rapid glacier retreat and depletion has been observed in most mountain and cold regions around the Globe (Zemp et al, 2019) including the Patagonian Andes (Davies and Glasser, 2012; Paul and Mölg, 2014; Masiokas et al, 2015; Falaschi et al, 2017; Dussaillant et al, 2019). Glacier studies usually relied on aerial photographs (e.g., Corte and Espizúa, 1981; Espizúa, 1983; among others for the Andes). The acquisition geometry of air photographs resulted in the deformation of terrain features (e.g., glaciers), which is maximized in areas of mountain topography. This in turn made the use of specific hardware (a photo restitutor) and precise ground control points usually obtained during field surveys mandatory, resulting in a highly complex process. The advent of techniques such as Structure from Motion (SFM) has allowed for assessing glacier changes during the pre-satellite era without such demanding efforts (Mölg and Bolch, 2017; Vargo et al, 2017)

Results

Discussion

Conclusion