<abstract xmlns="http://www.w3.org/1999/xhtml">

On February 7th, 2021, a rockslide of about 20 Mio m³ detached in a height of 5600 m asl. from the northern flank of Mount Ronti (Chamoli district, Uttarakhand state, India), turned into a rock mass fall and produced a debris flow. When the rock mass hit the Ronti Gad valley after a fall height of 1800 m the rock mass mixed with melting dead ice together with snow and ice avalanche material of previous debris flows. The debris flow destroyed hydroelectric infrastructure between 10 - 20 km down the valley killing 204 people either working at or visiting the power plants. By combining remote sensing, structural geology and kinematics/mechanical analysis of the rockslide, we demonstrate that a 600 m wide and almost 800 m long block of quartzite, bordered laterally by two joints and a newly formed tension crack on the top detached from an underlying layer of biotite-rich paragneisses. Assuming full hydrostatic heads in both joints and in the tension crack as well as 75% of the full hydrostatic head in the lower boundary surface between quartzites and paragneisses, the rock block analysis yields a friction angle of 32° for both joints, which is a plausible value of the friction angle of joints in quartzites. The detachment of the block has been the result of the widening of the tension crack on top, of a progressive propagation of the lateral joints together with a catastrophic failure of the detachment plane at the border between quartzites and paragneisses. At the time of the failure, all discontinuities must have been almost completely filled with water raising the question, if the frequency of rockslides in the Himalayas is increasing as temperatures rise and permafrost is thawing due to climate change.
</abstract>

On February 7th, 2021, a rockslide of about 20 Mio m³ detached in a height of 5600 m asl. from the northern flank of Mount Ronti (Chamoli district, Uttarakhand state, India), turned into a rock mass fall and produced a debris flow. When the rock mass hit the Ronti Gad valley after a fall height of 1800 m the rock mass mixed with melting dead ice together with snow and ice avalanche material of previous debris flows. The debris flow destroyed hydroelectric infrastructure between 10 - 20 km down the valley killing 204 people either working at or visiting the power plants. By combining remote sensing, structural geology and kinematics/mechanical analysis of the rockslide, we demonstrate that a 600 m wide and almost 800 m long block of quartzite, bordered laterally by two joints and a newly formed tension crack on the top detached from an underlying layer of biotite-rich paragneisses. Assuming full hydrostatic heads in both joints and in the tension crack as well as 75% of the full hydrostatic head in the lower boundary surface between quartzites and paragneisses, the rock block analysis yields a friction angle of 32° for both joints, which is a plausible value of the friction angle of joints in quartzites. The detachment of the block has been the result of the widening of the tension crack on top, of a progressive propagation of the lateral joints together with a catastrophic failure of the detachment plane at the border between quartzites and paragneisses. At the time of the failure, all discontinuities must have been almost completely filled with water raising the question, if the frequency of rockslides in the Himalayas is increasing as temperatures rise and permafrost is thawing due to climate change.

The detachment mechanism of the rockslide causing the Chamoli February 7th, 2021 debris flow disaster

Austrian Journal of Earth Sciences

This work is licensed under the Creative Commons Attribution 4.0 International License.

The detachment mechanism of the rockslide causing the Chamoli February 7, 2021 debris flow disaster

On February 7th, 2021, a rockslide of about 20 Mio m³ detached in a height of 5600 m asl. from the northern flank of Mount Ronti (Chamoli district, Uttarakhand...

The detachment mechanism of the rockslide causing the Chamoli February 7^th, 2021 debris flow disaster

Publié en ligne: 27 déc. 2022

Pages: 191 - 198

Reçu: 01 mars 2022

Accepté: 06 oct. 2022

DOI: https://doi.org/10.17738/ajes.2022.0009

Mots clés
Chamoli disaster 2021, mechanics of rock failure, back analysis, natural hazard

© 2022 R. Poisel et al., published by Sciendo

This work is licensed under the Creative Commons Attribution 4.0 International License.

The detachment mechanism of the rockslide causing the Chamoli February 7th, 2021 debris flow disaster

Publié en ligne: 27 déc. 2022

Pages: 191 - 198

Reçu: 01 mars 2022

Accepté: 06 oct. 2022

DOI: https://doi.org/10.17738/ajes.2022.0009

Mots clésChamoli disaster 2021, mechanics of rock failure, back analysis, natural hazard

© 2022 R. Poisel et al., published by Sciendo

This work is licensed under the Creative Commons Attribution 4.0 International License.

The detachment mechanism of the rockslide causing the Chamoli February 7^th, 2021 debris flow disaster

Mots clés
Chamoli disaster 2021, mechanics of rock failure, back analysis, natural hazard