On 7 Feb 2021, a catastrophic mass flow descended the Ronti Gad, Rishiganga, and Dhauliganga valleys in Chamoli, Uttarakhand, India, causing widespread devastation and severely damaging two hydropower projects. Over 200 people were killed or are missing. Our analysis of satellite imagery, seismic records, numerical model results, and eyewitness videos reveals that ~27x106 m3 of rock and glacier ice collapsed from the steep north face of Ronti Peak. The rock and ice avalanche rapidly transformed into an extraordinarily large and mobile debris flow that transported boulders >20 m in diameter, and scoured the valley walls up to 220 m above the valley floor. The intersection of the hazard cascade with downvalley infrastructure resulted in a disaster, which highlights key questions about adequate monitoring and sustainable development in the Himalaya as well as other remote, high-mountain environments.

This study analysed the actively surging Shisper Glacier in the Karakoram region of Pakistan using earth observation data from Landsat OLI and Planet images. Changes in the surface glacier velocity, supraglacial moraines and debris cover were assessed using Landsat 8 data at monthly time-steps from January 2018 to May 2019. High resolution data from Planet Labs was used to precisely detect the snout advance and ice-dammed lake expansion. Downstream cross-section profiles of the valley were generated using a moderate resolution digital elevation model to assess the inundation in the event of rapid ice-dammed lake drainage. Correlation Image Analysis Software working on the principle of normalized crosscorrelation was used to generate time series monthly surface velocity profiles for Shisper Glacier. Manual digitization at 1:30000 scale was used to delineate supraglacial moraines and supraglacial debris cover. The glacier surface velocity profiles indicate that the ablation zone of the glacier continues to be in an active surge phase resulting in advance of the snout and expansion of the ice-dammed lake. Surface glacier velocities are as high as 48 m d-1. Between 18 December 2018 and 8 May 2019, the glacier snout advanced at ~6 m d-1 with a total overall advance of 860 m. The lake formed due to damming of outflow stream from Mochowar Glacier expanded to its maximum area (29.69 ha) in May 2019 before drainage started on 23 June 2019. Our estimates indicate that the peak discharge in case of rapid drainage could vary between 5033 m 3 s-1 and 6167 m 3 s-1 and potentially affect infrastructure downstream.

Abstract. Glacial lake outburst floods (GLOFs) are among the most concerning consequences of retreating glaciers in mountain ranges worldwide. GLOFs have attracted significant attention amongst scientists and practitioners in the past 2 decades, with particular interest in the physical drivers and mechanisms of GLOF hazard and in socioeconomic and other human-related developments that affect vulnerabilities to GLOF events. This increased research focus on GLOFs is reflected in the gradually increasing number of papers published annually. This study offers an overview of recent GLOF research by analysing 594 peer-reviewed GLOF studies published between 2017 and 2021 (Web of Science and Scopus databases), reviewing the content and geographical focus as well as other characteristics of GLOF studies. This review is complemented with perspectives from the first GLOF conference (7–9 July 2021, online) where a global GLOF research community of major mountain regions gathered to discuss the current state of the art of integrated GLOF research. Therefore, representatives from 17 countries identified and elaborated trends and challenges and proposed possible ways forward to navigate future GLOF research, in four thematic areas: (i) understanding GLOFs – timing and processes; (ii) modelling GLOFs and GLOF process chains; (iii) GLOF risk management, prevention and warning; and (iv) human dimensions of GLOFs and GLOF attribution to climate change.

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This study reports the changes in glacier extent and streamflow similar to many Himalayan studies, but takes the unusual step of also linking these to downstream land use changes in Kashmir Valley. This study assessed changes in the area, snout, and equilibrium line altitude (ELA) of four parts of the Kolahoi Glacier using earth observation data from 1962 to 2018. Changes in the discharge of the two streams flowing out from Kolahoi Glacier into the Jhelum basin were also assessed between 1972 and 2018. Additionally, satellite data was used to track the downstream land system changes concerning agriculture, orchards, and built-up areas between 1980 and 2018. This analysis suggested a cumulative deglaciation of 23.6% at a rate of 0.42% per year from 1962 to 2018. The snout of two larger glaciers, G1 and G2, retreated at a rate of 18.3 m a −1 and 16.4 m a −1 , respectively, from 1962 to 2018, although the rate of recession accelerated after 2000. Our analysis also suggested the upward shift of ELA by ≈120 m. The streamflows measured at five sites showed statistically significant depleting trends that have been a factor in forcing extensive land system changes downstream. Although the area under agriculture in Lidder watershed shrunk by 39%, there was a massive expansion of 176% and 476% in orchards and built-up areas, respectively, from 1980 to 2018. The conversion of irrigation-intensive agriculture lands (rice paddy) to less water-intensive orchards is attributed to economic considerations and depleting streamflow.Water 2020, 12, 1168 2 of 18 to decrease in the streamflows in the Himalayan Rivers [7,[27][28][29], which could affect water availability downstream [30]. Studies suggest that the glacier recession in the Kashmir valley has already resulted in the depleted streamflows downstream [31,32]. The land system changes in the region [33][34][35][36] have been linked to depleting streamflows, economic considerations, and unplanned land transformation.The use of remote sensing data for quantifying land system changes over the Kashmir region has been widely documented [37][38][39][40]. At the same time, there is substantial scientific literature detailing the glacier retreat prevalent over the region. A recent study indicated that the glaciers in the Ladakh region are retreating at 0.55% a −1 [41], whereas another study [42] reported few stable and advancing glaciers in the Zanskar region of Jammu and Kashmir. Similar retreat estimates have been put forth for the Zanskar region for the glacier area changes carried between 1989 and 2007 [43]. However, very conservative area changes (0.16% a −1 ) have been reported for the neighboring Suru basin [44] for the glacier area changes assessed for the 1977-2017 period. In another study carried out in the Lidder watershed of the Jhelum basin, the glaciers were reported to be shrinking at 0.51% a −1 [17]. Glacier mass change over the western Himalayas has accelerated from 0.33 to 0.5 m w.e. (water equivalent) per year between 1970-2000 and 2000-2010, respectively [45]. Ther...