## 1 Introduction
Catastrophic failures at Samarco and Brumadinho in 2015 and 2019, respectively, brought mine tailings disasters onto the global level in unprecedented ways, and several studies have developed these themes following these events (e.g., [11; 12; 13; 14; 6; 15]). Another very serious failure event took place in 1985, at two tailings dams nearby the town of Trento in Northern Italy. The collapse triggered a disastrous mudflow [17] that destroyed the villages of Stava and Tesero, killing 268 people. In this case, human factors contributed most to the failure; the dam's superstructure which did not meet high safety standards [18] and the failure of the two dam bodies can be explained through excess amount of water in the tailings pond and liquefaction by infiltration phenomenon [19; 20]. The assessment of tailings dam stability involves the study of the hydrogeological settings, tailing material characterization, deposition methods and of the possible trigger factors leading to dam failure (e.g., earthquakes, extreme rainfall, man-made factors [21]). However, the monitoring of deformations of the dam body is also of primary importance, even if it is challenging due to the size and inaccessibility of these facilities, which are among the world's largest engineered structures. In-situ geotechnical instruments, levelling, total stations, or GNSS and visual inspections represent the conventional labor-intensive and time-consuming monitoring systems generally used at tailings dams. However, traditional techniques are conducted on a point-by-point basis with limited spatial coverage [22]. Satellite remote sensing technologies such as Synthetic Aperture Radar (SAR) Interferometry (InSAR), can overcome this limitation, allowing for the analysis of wide areas, and ability to obtain information from the past, using data archives. This consolidation technique can be an effective tool for the engineers in charge of structural health monitoring of dams (e.g., [23; 24; 25; 26; 27]) and tailings dams [14; 15; 16; 22; 28]. Specifically, Advanced Differential SAR Interferometry (A-DInSAR) can provide information about the ongoing and past deformations with millimeter accuracy and can be used for the prediction of catastrophic events (e.g., [12; 15]), by the detection of precursory deformation at the dam structure before the failures occur. This paper focuses on the deformation phenomena that affect the tailings dam of Zelazny Most (Figure 1) using satellite A-DInSAR. The Zelazny Most Tailings Storage Facility (TSF) is the largest sumy reservoir in Europe built using the upstream method (Figure 1d, [1; 29]) and is one of the largest in the world. It stores the waste derived from copper extraction activities of the adjacent Legnica Glogow Copper District (LGCD, Poland) the most important copper mines of Lower Silesia, managed by the KGHM Polska Miedz S.A. For more details on the mining basin and on the superficial deformation phenomena that affect it, see [PERSON] et al., submitted to this journal. More than 99% of the original ore extracted in the copper mines of Lubin, Rudna, and Polkowice-Sieroszowice (Figure 1c) represents waste: everyday an average of 80,000 tons of waste derived from the mechanical separation processes are produced [29] and then discharged in the basin, by means of flotation. Figure 1: Zelazny Most Tailings dam and adjacent Legnica Glogow Copper District (LGCD); (**a**) location of the study area; (**b**) aerial photo of Zelany Most; (**c**) location of the tailings dam and borders of LGCD mines in yellow (from [[http://dm.pggi.gov.pl/](http://dm.pggi.gov.pl/)]([http://dm.pggi.gov.pl/](http://dm.pggi.gov.pl/)), accessed on 2 May 2021); (**d**) schematic cross-sections of a ring dam (modified form [1], reprinted with permission from [1]. 2014, ICE Publishing).