Creeping slopes in NW Himalaya and Joshimath slide: constraints from GPS measurements

Abstract

Slow slope movement is very common in the Himalayan region. In most cases, the topsoil, weathered rock mass, debris of paleo-landslide or of glacial origin, etc. slowly slides until it stabilizes or fails. In some cases, even the bedrock may be involved in sliding. Here we report four such sliding slopes on which GPS were actually installed for tectonic deformation monitoring in the Himalayan region after a careful investigation but they recorded slow slope sliding. The slow sliding motion on these slopes varied from 10-15 mm/year to 5-6 m/year. The slow slides did not show any anomalous seasonal variation due to hydrological loading. Amongst the four, the Joshimath slide exhibited a large variation in sliding motion which varied from less than a mm/day to 15 mm/day during 2022-2023, causing cracks on the ground and buildings and panic amongst the residents. Even the highly non-linear motion with a sudden change in sliding motion at Joshimath appears to be of viscous creep type. The exact time of initiation of this episode of slide is not known but the available InSAR analyses imply that it is moving at least since 2018. Its motion does not seem to be affected by the February 7, 2021 floods, however, whether the anthropogenic activities around the sliding zone influenced its motion and initiation, remains to be debated.

Keywords:

• NW Himalaya
• slow moving slope
• GPS measurements
• Joshimath landslide

Acknowledgements

We thank Survey of India for providing GPS data from Joshimath and Rudraprayag sites. GPS data from other sites are from the CSIR-NGRI network. We thank two anonymous reviewers and the Editor for their constructive suggestions. This is NGRI contribution number NGRI/Lib/2023/Pub-80.

CRediT authorship contribution statement

Conceptualization: VKG; methodology: VKG, NG, SPS; Data acquisition: NG, AvK, AmK, RKY, AM, SPS; formal analysis and investigation: VKG, SR, RKY, SPS, AM; writing first draft: All authors; review and editing: VKG, NG, RKY, SR, AM; approval of final draft: All authors; supervision: VKG.

Disclosure statement

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Additional information

Funding

No funding for this work has been provided for this work and the work for this ms has been done on purely academic collaboration.