Joshimath under Strain, A Scientist’s View Point (Part-1)
Media is full with cries of “Joshimath is sinking”. Is that really the case? No, the narrative is untrue. Joshimath has several entities of territories. Firstly, there are several mountains with solid steady rocky bases which are stable although vulnerable to tremors which may also inflict cracks/wear and tears depending on the types of rocks. These Rocky Mountains may have steep or reasonably shallower slopes which are more or less stable. Dwellings are difficult to make over these mountains but they remain stable. Secondly, some of the shallow slopes of some of the mountains/hills are the result of centuries old severe land/mudslides as a result of high intensity quakes over which both primary or secondary soils form over time (of centuries/millennia). These surfaces are relatively unstable, capable of bearing only limited loads. If overcrowded with concrete dwellings, it may show signs of sinking. However, a surface may also be commensurate with a regular mountain slope or a stable valley on which any type of inhabitation whether dense or space, will be stable. Thirdly, the basin (or the base of a narrow valley) which is bound to have at least some amount of unstable surface that may cave in the future. In Himalayan mountains, the deepest part of the valleys are invariably occupied by rivrs/streams where seldom any inhabitation develops owing to recurrent flash floods and some other issues.
Coming back to Joshimath, one or more of the above effects have been creating a distinct impact on the ground. The past earthquakes in the region have been worrisome that mandated the govt to set-up various study groups from time to time. The main reports among those are the 1977 Mishra Committee and 2006 Wadia Instt of Himalayan Geology reports. Both these reports had suggested of the vulnerability of the unstable sub-soil ‘Gneisses and Schistose rocks’ liable to subside below and cause the overground features to sink. This has also been aggravated by lack of sewage/sullage system in the major part of city. What we observe today of sinking Joshimath, has been augmented by unplanned heavy dwelling constructions overhead. In layman’s terms if Joshimath subsoil was capable of withstanding a load of ‘x’ Gegatons of weight, the proliferation of rapid constructions have loaded the area with ‘x++’ loads that is causing it to sink. Besides, in the last few weeks, sink rate is understood to be increasing rapidly. Besides, the vibrations of constructions and recurrent seismic activities must also be adding up to the subsidence. Further, there are subsoil water flow whether of the streams getting underground along with the non-channelled sewage/drainage water…all together adding up to the basic problems of softened subsoil vulnerable to further subsidence. Some biased groups have blamed NTPC hydro-electric project going on 13 km away, for the subsidence of Joshimath that may be a flawed allegation, without any proof. Besides, other factors such as land/mudslides down the slope too cannot be ruled out.
The present crisis is mainly on the shallow secondary/unstable slope of only part of the mountainous features (ward 1, 4, 5 & 7) extending upto the river basin. These one slopes cannot be compared or equated with the other slopes that have solid rock bases underneath. Reports are also coming of minor cracks developing in the dwellings at the slopes of other mountain/hills of Joshimath as well as elsewhere in the Himalayan region of Karna-Prayag, Rudra-Prayag and Chamoli hills.
Joshimath is a warning to India and the world of over-inhabitation in unstable mountainous terrain. An unstable surface forms in an area where there is secondary crust formation in the earth due to various reasons. The reasons are mainly the formation of soil as a result of collisions of the tectonic plates. When tectonic plates collide, various grades of tremors are felt by all followed by the consequences of sub-soil rise following convergent collision; or depression following divergent type of collisions. The cause-effects are commensurate with its severity of the collisions. It is also possible for some of the convergent type of high intensity tremor convergent collisions to rip apart the surface of earth which is usually shallower. However, what is not visible on the surface, is the sub-soil changes. Thus tectonic collisions cause several surface and sub-soil phenomena, some adversely affecting the characteristics of the surface, the prominent ones as mentioned below:-
The subsoil effects of the earthquakes can be understood better as per the type of tectonic plate collisions whether it is of Convergence or Divergent types. Convergent types of collisions cause prominent tremors (often leading to surface cracks) and rise in the soil levels. On the other hand, Divergent type of collisions causes the tectonic plates to drift apart. If accompanied with volcanic effects, may cause a rise of the soil otherwise, will lead to caving with deep and wide fissures as shown below.
Coming back to Joshimath, one or more of the above effects have been creating a distinct impact on the ground. The past earthquakes in the region have been worrisome that mandated the govt to set-up various study groups from time to time. The main reports among those are the 1977 Mishra Committee and 2006 Wadia Instt of Himalayan Geology reports. Both these reports had suggested of the vulnerability of the unstable sub-soil ‘Gneisses and Schistose rocks’ liable to subside below and causing the overground features to sink. This has also been aggravated by lack of sewage/sullage system. What we observe today of sinking Joshimath, has been augmented by unplanned heavy dwelling constructions overhead. In layman’s terms if Joshimath subsoil was capable of withstanding a load of ‘x’ Gigatons of weight, the proliferation of rapid constructions have loaded the area with ‘x++’ loads that is causing it to sink. Besides, in the last few weeks, sink rate is understood to be increasing rapidly. Besides, the vibrations of constructions and recurrent seismic activities must also be adding up to the subsidence. Further, there is subsoil water flow whether of the streams getting underground or the non-channelled drainage water…all together adding up to the basic problems.
The present stress and strain on the surface of Joshimath has caused the ground and buildings to crack, gap or sink (subside) by varying extents. This has endangered the affected dwellings to collapse unpredictably. Any significant tremors in future will cause major collapse and devastation of these dwellings hence, many such affected dwellings are totally unsafe for living.
The concrete dwellings grown on the surface of Joshimath cannot be removed. Hence, sinking of the ground with concurrent collapse of the dwellings are unavoidable. In the initial stage it was only Gandhinagar (Ward-1), Singhdwar (Ward-4), Manoharbagh (Ward-5) and Sunil (Ward-7) localities of Joshimath at risk. Actually Hotel Mount view located on the higher slope downward till Alakhnanda rive is showing various grades of cracks. It is good that govt has evacuated people presently from about 600-odd dwellings in the most vulnerable areas with cracks. However, problems seem much larger than the eyes can see.
There are reports of about 60-odd High Tension power Towers (HTT) tilting in and around Joshimath. Further, cracks similar to Joshimath have been observed elsewhere in Karnprayag, Rudraprayag etc. All these also mean that construction on the unstable soil of past landslides may not be the only reason for sub-soil stresses and subsidence in the region. The adjacent areas may also be more or less equally vulnerable owing to reasons over and above the sub-soil subsidence, with or without additional concrete constructions because HTTs are also tilting. Scientists having expertise in regional geology may be tasked to ascertain the extent of the vulnerable areas. Then only, the population may be relocated in semi-permanent non-concrete dwellings. Such lightweight dwellings only will be compatible in those vulnerable areas.
The above reasoning leaves one important aspect of issues untouched that is what environmentalists and climate activists often talk. These issues include developmental activities of creating infrastructure of roads, tunnels and hydropower projects. There is surely no doubt that the above activities without stabilisation of the slopes and caves/tunnels could cause frequent landslides / tunnel cave-in in future. However, these effects may not be directly related to the sub-soil subsidence that we observe in Joshimath and elsewhere. These could be an important issue in the change of ecology and mudslides along the cut and un-stabilised mountain slopes. Even the methodology of such infrastructure creations, whether with heavy equipment or limited rock explosions causing some vibration/tremors, may have very limited impacts on soil subsidence 10s of kilometre away. While the land/mudslides do take place even in the zones not having such developmental projects, it is more frequent along the improperly constructed roads/infra. Hence, while creating infrastructures in mountains, it is very important to stabilise the cut slopes with additional safety factors for the loads that the future formation of soil may cause. There must not be any complacency in this regard…BUT…that is what is happening more often than not; in most of the slope cutting, by most of the govts. It is re-emphasised here that these infrastructure developments may not have direct impact on Joshimath types of phenomena.
(Note-The author will be visiting the affected areas with the intent to study topography in late Jan & early Feb 2023 and come up with further information on the subject in part-2 of the article.)