Study of Flash Flood in the Rishiganga and Dhauliganga Catchment in Chamoli District of Uttarakhand, India

The present study is an attempt to investigate a flash flood that occurred on the morning of 7th February 2021 in the Rishiganga and Dhauliganga Catchments in Chamoli District of Uttarakhand. A catastrophic flood was triggered due to a massive rock-cum-snow avalanche caused by Antecedent Snow falls in the region. A huge flash flood was generated as a tremendous quantity of rockslide, comprising deposited ice and snowmelt, rolled down the Ronthi Glacier and flowed downstream into the glacier valley. This massive flash flood hit the NTPC's Tapovan-Vishnugad hydel project and the Rishiganga Hydel Project, bridges, roads, and communities in and around Raini, Tapovan and Joshimath regions in the Chamoli district of Uttarakhand. The mud and slush-inducing elements resulted in the development of a dammed lake, which momentarily blocked one of the Rishiganga's tributaries. Temporal satellite image has been used to access the information of disaster damage assessment in the region. The high-resolution satellite image clearly showing flash flood watermarks in the region and on the avalanches site rock outcrops reaching up to 50–130m height on the way to Raini Gaon. As part of our analysis, we have also looked at the valley's slope profile, which clearly shows the valley's height following the destruction. It is estimated that more than Rs 4,000 crore infrastructures loss due to this flash flood in the region. Besides, two bridges have also been lost. Hydometeriological analysis was also carried out in order to obtain the trend of rapid increase in temperature in the valley where disaster occurred. Using remote sensing (RS) and Geographic Information System (GIS) techniques, thematic layers were generated for obtaining information on the flash flood.

The shape and infill of the Basadingen overdeepened glacial valley from P-wave seismic reflections

<p><span>Overdeepened valleys in the Alps allow to probe the glacial sedimentation record, which in turn can illuminate the climatic history. In particular, seismic reflections can be used to extend punctual borehole data (for instance a number of boreholes are to be drilled into Alpine glacial overdeepened valleys as part of the DOVE ICDP project) in the second dimension or even survey a region before drilling begins. Thus, we use detailed, 2-D seismic P-wave profiles to reveal the shape and infill of an overdeepened Rhine glacier valley in the area of Basadingen, near to the German/Swiss border. We acquired two profiles nearly perpendicular to the valley strike, approximately 500 m apart. The first profile was 1246 m long, and consisted of a single spread of 624 geophones. The second profile was 1120 m long and was acquired using 200 3-component geophones using a roll-along method. For both profiles we used a vibro-source with a 12 s linear sweep of 20-240 Hz at every second geophone (two metre spacing), which produced a high fold.</span></p><p><span>Both seismic images reveal that the overdeepened basin at this location is asymmetrical and circa 260 m deep, although the deepest part (220</span><span> </span><span>m wide) covers only a small portion of the broader main valley. The infill is characterised by at least three unconformities and distinct onlap and erosive boundaries between the sedimentary units. We interpret the infill to represent a highly dynamic sedimentary system. The lower part, within the deepest part of the basin is filled with chaotic sediments and slumping. Above a major unconformity, the upper part contains strongly-dipping reflectors that probably represent a prograding point-bar in a glacio-fluviatile environment that migrated toward the north-east. Beneath the deepest part of the basin we see evidence for faults in the Tertiary Molasse basement, which correlate with known faults at the surface. The faults most likely caused the valley to be sited at this location and they were probably also the cause of the ‘valley in valley’ shape.</span></p><p><span>A new DOVE research borehole will be drilled in the centre of the valley in 2021. This will bring more light on the sedimentary history and OSL-dating of the material will bracket the timing of the infill. </span></p>

New Late Glacial and Holocene 36Cl and 10Be moraine chronologies from sub-Antarctic Kerguelen Archipelago

<p>The Kerguelen Archipelago (49°S, 69°E) is an excellent location for the study of multi-millennial glacier fluctuations, since it is the largest still glaciated emerged area (552 km<sup>2 </sup>in 2001) in the sub-Antarctic sector of the Indian Ocean, where many glacio-geomorphological formations such as moraines may be dated. To investigate the so-far little-known Late Glacial and the Holocene glacier fluctuations in Kerguelen, we apply cosmogenic nuclide dating of moraines in 3 glacial valleys: Val Travers valley, Ampere glacier valley and Arago glacier valley. We use in situ <sup>36</sup>Cl dating of the basaltic moraine boulders at the first two sites, and <sup>10</sup>Be dating of the quartz-bearing syenite boulders at the third site. The new <sup>36</sup>Cl and <sup>10</sup>Be exposure ages provide time constraints over the last 17,000 years. A glacial advance was highlighted during the Late Glacial at 14.4 ± 1.4 ka ago, probably linked to the Antarctic Cold Reversal event. These results are consistent with those previously obtained on the archipelago (Jomelli et al., 2017, 2018; Charton et al., 2020) and more generally those from other the sub-Antarctic regions (<em>e.g.</em> Sagredo et al., 2018). This suggests that all glaciers at this latitude were broadly sensitive to this specific climatic signal. No Early nor Mid Holocene advances were evidenced in Kerguelen glacier evolution during the Holocene due to missing moraines that may have formed in these specific periods. Radiocarbon-dated peat, published in the 1990s, provides evidence of less extensive glacier extents during the Early Holocene than during the Late Holocene (Frenot et al., 1997). Finally, glaciers seem to have re-advanced only during the Late Holocene, especially within the last millennium, at ⁓1 ka, ⁓620 years and ⁓390 years (Verfaillie et al., submitted). A comparison of this new dataset with the available <sup>10</sup>Be ages from other sub-Antarctic regions allows for the identification of 3 different glacier evolution patterns during the Holocene. The glacial fluctuations experienced by Kerguelen glaciers seems particularly uncommon, and are likely due to its singular location in the Southern Indian Ocean. Finally, climatic factors that may explain the Kerguelen glacier evolution (temperature, precipitation) are discussed. To this end, we investigate the chronology of glacier advance/retreat periods with <em>(i)</em> the variation in atmospheric temperatures recorded in ice cores in Antarctica and <em>(ii)</em> the variation in precipitation (Southern Westerly Winds, Southern Annular Mode).</p><p>Charton et al., 2020 : Ant. Sci. 1-13</p><p>Frenot et al., 1997 : C.R. Acad. Sci. Paris Life Sciences 320, 567-573</p><p>Jomelli et al., 2017 : Quat. Sci. Rev. 162, 128-144</p><p>Jomelli et al., 2018 : Quat. Sci. Rev. 183, 110-123</p><p>Sagredo et al., 2018 : Quat Sci. Rev. 188, 160-166</p><p>Verfaillie et al., submitted</p>

Misinterpreting proxy data for paleoclimate signals: A reply to Srivastava and Jovane, 2020

Srivastava and Jovane (2020) have made several comments on our assessment of proxy data and challenged the outcome of Shukla et al. (2020) based mainly on interpretation of environmental magnetic parameters. We respond to their criticisms and re-evaluate our paper, remove ambiguities and validate our conclusions through additional proxies (grain-size and geochemistry). We welcome their comments and do not entirely rule out their interpretation for magnetic mineralogy. We highlight the importance of proxy validation for high-energy environments like Chorabari lake. However, single proxy data correlation is likely to produce biased results with no relevant meaning. The objective of our study was to understand complexities in the glacial-climate system by reconstructing late-Holocene climate variations using the glacial lake sediment records from the Mandakini River Basin, Central Himalaya, India. We presented the complexities in Shukla et al. (2020), and this was also highlighted by Srivastava and Jovane (2020). In response, we provide additional justification of proxy response and substantiate our results with present-day estimates from the Chorabari glacier valley. We disagree with the thesis put forward by Srivastava and Jovane (2020) in their conclusion as they overemphasize the interpretation of a single proxy. We maintain that the investigation of present-day glacial settings is an important precursor of paleoclimatic data interpretation and that this supports our conclusions. We will try to incorporate the important suggestions of Srivastava and Jovne (2020) relating to the interpretation of magnetic data in future work.

The geomorphic impact of large landslides: A case-study of the actively moving Alpine Gardens Landslide, Fox Glacier Valley, West Coast, New Zealand.

<p>Large landslides can result in significant geomorphic impacts to fluvial systems, via increased sediment input and subsequent changes to channel behaviour. We present a case-study of the actively moving  ̴65 M m³ Alpine Gardens Landslide in the Fox Glacier Valley, West Coast, New Zealand, to analyse the ongoing geomorphic impacts within the valley floor. Debris flows, sourced from the toe of the landslide, travel down Mill’s Creek and deposit sediment on the debris fan at its confluence with the Fox River. This debris flow activity and associated changes in sediment flux and fluvial behaviour have resulted in re-occurring damage to, and current closure of roads and tracks within the Fox Glacier Valley floor, impacting access to the Westland Tai Poutini National Park, the Fox Glacier, associated tourism, and the Fox Glacier township economy.</p><p>Initial movement of the Alpine Gardens landslide was detected in 2015, with aerial imagery analysis between March 2017 and June 2018 indicating that the landslide may be accelerating. This acceleration may potentially result in increased debris flow activity within the landslide complex and sediment flux into the Fox River. To monitor and understand the controls on movement rate, we installed a continuous GPS monitoring station along with rainfall gauges on the landslide in February 2019. On average, the landslide moves at a rate of 0.12 m/day ± 0.13 m/day, however this rate of movement of the landslide is closely correlated to and fluctuates with rainfall. Significant accelerations of 0.5 m/day have occurred after heavy rainfall, with these rainfall events also resulting in large debris flows.</p><p>We document and investigate the geomorphic impact of the Alpine Gardens landslide on the Mill’s Creek debris fan and Fox Glacier Valley floor via terrestrial laser scanning, airborne LiDAR, UAV surveys and aerial imagery. From this, we derive a time-series of nine surface change models to document the sediment flux within the Alpine Gardens Landslide and Mill’s Creek debris fan complex. Our initial results reveal that between March 2017 and June 2019, approximately 14.7 M m³ was eroded from the landslide, of which 3.7 M m³ was deposited directly on the debris fan. A further 9.6 M m³ has been transported downstream into the fluvial system. Upstream aggradation has also occurred, with 1.1 M m³ deposited in the river valley immediately upstream of the debris fan between June 2018 and June 2019. Continued monitoring of the Alpine Gardens Landslide and volumetric changes of the landslide complex allows us to understand the controls on the movement and sediment flux within the landslide and the geomorphic impact of large actively moving landslides on the valley floor, particularly within alpine and glacial environments. </p>