Geological contributors to rapid development: Understanding the causes of the Joshimath catastrophe

The development of cracks and ground fissures in Joshimath, a holy town situated on ancient landslide residue in Chamoli district, may have been influenced by geological instability, rampant development (over 4200 buildings), and traffic-induced vibrations, according to nine technical reports of central government institutions on Joshimath. The state and federal governments ordered the studies to learn more about the many facets of the town’s unexpected cracking between November 2022 and January 2023.

Magnitude

The central, eastern, and southern (high altitude) portions of Joshimath town indicated a greater rate of land displacement, around 12 cm per year, as compared to other locations, according to the Indian Institute of Remote Sensing (IIRS) study on Deformation Analysis.

Between June 2019 and February 2022, IIRS analyzed satellite images of Joshimath and provided a variety of explanations for “subsidence,” including “toe-cutting” by the Alaknanda river, which flows at the toe/base of Joshimath hillside, slope instability caused by local drainage water seeping into the soil, loose and unconsolidated moraine materials of the slope (due to old landside), and flash flood events that have recently occurred in the area.

According to the report, there was a sudden increase in deformation from November 9, 2022, to January 19, 2023, due to an increase in underground land displacement in the vertical direction, primarily as a result of higher underground water flow. “This resulted in the development of cracks in the ground as well as houses in Joshimath town,” the report said.

Geographical factors

The Joshimath slope experienced over 6 cm of displacement between December 2022 and January 2023, according to a report on the study of geological and geotechnical subsurface strata at Joshimath by the National Institute of Geophysical Institute, Hyderabad. Peak subsidence regions also experienced fissures up to one meter in length both horizontally and vertically.

According to the analysis, Joshimath’s loose material covering solid rock is not consistent, with its greatest thickness being found along rivulets and streams. The zones with dense cover are where the majority of the ground cracks have been seen.

Joshimath has loose soil with low shear strength characteristics even at greater depths, according to a research of a similar kind conducted by IIT Roorkee. The research also said that “high-rise building overloads, land subsidence, and low soil resistance may exacerbate slope failures.”

The Main Central Thrust (MCT) fault-line, which runs close to Joshimath at Helang and makes the rocks structurally weak and sheared, may worsen the ground condition, according to the paper. As a result, the region around Joshimath town is covered by a heavy layer of overburden material (a very ancient landslide), and it has been gradually sinking for a long time, according to the study. The Mishra Committee was the first to publicly disclose this issue in 1976.

Given that Joshimath is located in a high seismic zone, fissures may widen, according to the Wadia Institute of Himalayan Geology (WIHG). Within 50 kilometers of Joshimath, between January 13 and April 12, 2023, 16 microearthquakes with a maximum magnitude of 1.5 were detected by WIHG’s seismic network. A few earthquakes of larger magnitude, including one measuring 5.4 on the Richter scale on January 24, 2023, were noted within a 100 km radius. “The present and past seismic activity has a similar trend of increasing seismicity to the south and southwest, mainly concentrated around the epicentre of the Chamoli earthquake,” the paper said.

Human influence

The Central Building Research Institute (CBRI) evaluated 2,364 properties for its “Safety Assessment of Buildings in Joshimath” study, which noted that “excessive vibration” in the ground brought on by traffic was the major reason for fractures in homes and land. A total of 40 earth fissures with a depth of 3 to 4 meters and a width of up to 300 mm were also noted in the research. According to CBRI, of the total number of structures, 37% were “usable,” 42% required “further assessment,” 20% were “unusable,” and 1% “need to be demolished.”

While the majority of papers blamed Joshimath’s terrain for fractures, the Central Water Commission’s study on hydrology identified the many development projects in Joshimath Town’s spring zone as the primary cause. According to the report, this “stopped the flow” of spring water, causing it to leak into JP residential colony. “As large number of pilgrims for Chardham Yatra and tourists come every year, to provide accommodation, ample number of hotels, homestays are constructed in the area,” the report added.

NTPC delinking

According to the National Institute of Hydrology, Roorkee’s study, the National Thermal Power Corporation’s nearby hydro-projects are not to blame for the water spilling in JP Colony. Instead, it explained the phenomenon as being related to “subsidence” and underground water in the form of several springs in Joshimath’s western region. According to the report, the topography (a cascade of flat and steep terrain from top to bottom) and geological environment do not favor the development of long-term water channels to dispose of water from upper reaches, and any obstruction can lead to underground storage, which aggravates subsidence.

A total of 81 ground fissures were discovered by the Indian Geological Survey, 42 of which were recent and predominantly in areas with “excessive rate” water flow. It ascribed them to the Joshimath slope having a dense, loose, unconsolidated mass of debris as a result of the soil sinking during the previous four to five decades and naturally occurring subsurface seepage lines. The Tapovan-Vishnugad Hydel Project and JP Colony’s water sample testing did not agree, according to the study.

The Post Disaster Needs Assessment (PDNA) for the state was created, according to Dr. Ranjit Kumar Sinha, Secretary of Uttarakhand Disaster Management, on the basis of these studies. He stated that the Union government had received the report. “The report will be utilized to help stabilize the community. Additionally, the Public Works Department has been informed for future action.