Cause and Process Mechanism of Rockslide Triggered Flood Event in Rishiganga and Dhauliganga River Valleys, Chamoli, Uttarakhand, India Using Satellite Remote Sensing and in situ Observations

Abstract

The catchments of Rishiganga and then Dhauliganga valleys in the Chamoli district of Uttarakhand were impacted by a catastrophic flood triggered due to a massive rockslide, caused by wedge failure on 7th February, 2021. It is estimated that the massive rockslide of * 23 million cubic meter volume containing base rock, deposited ice, and snow got detached from the northern slopes of the Trishul mountain range near Ronti Glacier and created a vertical fall of almost 1700 m before severely impacting the Ronti Gad valley located at 1.5 km downstream of Ronti Glacier snout. The huge detached mass of rock and ice (GLIMS ID: G079733E30381N) swiftly moved downstream through the glaciated valley entraining snow, debris, mud on its way, caused rapid fluidization, created massive water/slush waves, and washed away partially or completely the hydel power projects and bridges in its route. It is estimated that * 0.93 Peta Joules of potential energy led to the generation of a significant amount of kinetic and thermal energy, good enough to trigger above-mentioned processes. Post-event analysis of high-resolution satellite data shows flood water marks in the valley and on the rock outcrops reaching up to * 80-150 m height on the way to Raini Village. The mud and the slush produced through this process led to the formation of a dammed lake and temporarily blocked one of the tributaries of the Rishiganga joining from the northeast. This study provides an insight into the sequence of events as they unfolded, through multi-temporal satellite image analysis, aerial survey, seismological data in conjunction with various other geo-spatial and geo-visualization tools for unraveling the flood event that has happened on February 7, 2021. We also discuss the potential cause of rockslide and the process mechanism of this unique event, causing loss of lives and property besides widespread devastation.

Modelling Permafrost Distribution in Western Himalaya Using Remote Sensing and Field Observations

“…However, in response to the increase in annual average temperature, the permafrost is depleting in many regions globally, including the Himalaya. The thawing of permafrost can have diverse and widespread impacts on society, such as an increase in landslides and land degradation due to destabilization of slopes [6][7][8][9], ground subsidence [10][11][12], changes in subsurface hydrology [13][14][15], damage to infrastructure [16,17], and change in sediment load of rivers [18]. More importantly, as the permafrost thaws, it releases greenhouse gases from the stored soil organic carbon, which creates positive feedback and further amplifies the rate of rise in annual average temperature [19][20][21].…”

“…The present study will serve as an analogue for future permafrost studies that will help in understanding the dynamics of permafrost in a changing environment and has implications for discerning the impacts of permafrost thawing on the evolution of potential natural hazards that may affect the high mountain communities. This becomes critical considering the higher rates of warming than the global averages [59][60][61][62] and increasing frequency of disasters in permafrost areas [9,63] observed in the Himalaya.…”

The Landslide Hazard Chain in the Tapovan of the Himalayas on 7 February 2021

“…The flood caused more than 200 fatalities or missing individuals (Shugar et al, 2021). It was one of the most catastrophic geo-disasters on record in this region, and attracted wide attentions (Martha et al, 2021;Meena et al, 2021;Pandey et al, 2021;Rana et al, 2021;Shrestha et al, 2021).…”

7 February Chamoli (Uttarakhand, India) Rock-Ice Avalanche Disaster: Model-Simulated Prevailing Meteorological Conditions

“…The event took place in the Tapovan area of Joshimath in the Chamoli District of Uttarakhand, India on 7 February 2021 at 4:51 UTC [51][52][53]55] (Figure 1A,B). During this event, a massive rock and ice avalanche happened approximately 22 km upstream of Tapovan Hydropower Project, below Ronti peak in the Nanda Devi massif [51,53,55], which led to a sequence of events that resulted in the loss of many lives and the infrastructural damage of two major hydropower projects in the Rishiganga and Dhauliganaga valleys (Figure 1C).…”

“…The triggering factors behind this rock-ice avalanche event could be unusual local meteorological conditions (temperatures, precipitation, winds speed and pattern, wind stress, radiative and turbulent fluxes, etc. ), climatic conditions (long-term changes in surface and air temperatures and precipitation patterns), and geological factors (extremely steep slope, destabilization of the rock due to the decreased ice cover, seismic activity) [28,[51][52][53][54].…”