A strange coincidence: Landslide on NH10 at Sethi Jhora on 23Sep2020 and again on 23Sep2023 at exactly the same spot.

On 23Sep2020 a landslide occurred on the National Highway 10 (NH10) at Sethi Jhora, which was covered in the STH blog.

Of the 114km between Siliguri and Gangtok, 90km of the NH10 lies in the mountains and of this approximately 65km is along the banks of the Teesta where a number of dams have been constructed. Now IRCON is also building a tunnel for a railway which when finished approx next year end will link Sevoke with Rangpo in Sikkim.
NH10 is the lifeline for the state of Sikkim and Kalimpong and also a strategically important road and supply route for the Indian Army.

I have reproduced a press clip & photo from the STH blog dated 26Sep2020 below:

Exactly, 3 years later at the same spot (Coordinates 26.93946N 088.44148E, Elvn 233m) and again on 23Sep, an almost identical landslide occurred due to which National Highway10 from Siliguri to Gangtok is closed for traffic since 24Sep2023 (see image below) till date.

Rainfall in Kalimpong on 23Sep2023 was 58.4mm
Annual rainfall in the Teesta Valley is approx 2500-3000mm. The entire region is in Seismic Zone IV.
Why the failure occurred?
I think there are 2 factors at play. First, the Darjiling-Sikkim Himalaya is riddled with out-of-sequence faults that have been active recently. The Seti Jhora practically runs along the reactivated Ramgarh thrust fault core. Such fault cores consist of powdery crushed material that have very little strength.  The roads that run over such zones have much lower strength and load carrying capacity. If you saturate such zones with water chances are that they will liquify and cave in. September end would be a time where the monsoon has been around for a while and has saturated these zones particularly when a reservoir is also underneath it. Such a cave-in also happened in the Birrik fault core last year on the side of the road. No reservoir was involved there. Just the fault core material and rain.

- Prof Malay Mukul, Dept of Earth Sciences, IIT Mumbai

Images of Sethi Jhora (NH10) from STH's archives (2016)

Update on 27Sep2023
I was informed by a Govt Official that NH10 at Sethi Jhora was open for single lane traffic at 11.30am ie after 3 days of closure

Praful Rao
Kalimpong district
Darjeeling-Sikkim Himalaya
savethehills@gmail.com
9475033744

STH Activities : Landslide Survey on the eastern flanks of Kalimpong (14July2016)

 14th Mile Landslide

The 14th mile 'sinking zone' lying on the eastern face of the Kalimpong ridgeline is one of the old landslide areas of this town. It is repaired on annual basis and is rumored to be a "blessing" to many a contractor - except that now with population growing and even a posh hotel coming up directly above this site, it will also be a curse to quite a few.
When I visited the site on 14Jul2016, I found that a portion of the road to Algarah had sunk considerably (slide 'A') and worse still the culvert next to it had also sunk (slide 'B') - and ALL the water from the culvert was percolating into the crack (slide 'C') acting as a lubricant to an unstable hillside ready to slide down.
Coordinates :
27°05´27.6” N

088°31´57.0”E
Elevation : 1372m

Landslide blocking Kalimpong - Lava Road

With our main road to the external world, NH10 always in a precarious state during the monsoons, we rely on the Kalimpong- Lava- Gorubathan road as our an alternate route to the plains. Unfortunately, this road also has quite a few 'hotspots' which keep the BRO busy during the monsoons.
On Sunday, 10July2016 at around 1600h, following the 125mm rainfall of Saturday, a portion of this road near Rickisum gave way. It remained blocked for 4 days and effectively cut off Lava and much of the eastern parts of sub-division from Kalimpong town.

Coodinates :

27°05´49.5”N
088°36´22.6”E
Elevation : 1804m

Praful Rao,

Kalimpong,

Dist Darjeeling

Light at the end of the tunnel? : Tindharia/ Pagla Jhora landslides to be repaired soon.

STH has been associated with the Tindharia and Pagla Jhora landslides from Nov2011 when we did a big, well-attended workshop at Tindharia.
Thereafter, in July this year, after further landslides directly threatened the DHR workshop at Tindharia, we spent an entire day in the area checking the drainage and preparing a report for an expert and a friend (see here).
I am glad to say that the PWD will finally be taking up repairs of both the above landslide areas in the near future. You can read the Telegraph article here and this move I am sure, comes directly as an aftermath of the visit to Kolkata by the high powered NDMA team early this week (read here)

My only fear is, that is it too little - too late?

Because the way our bureaucracy groans and grinds along, by the time the work ACTUALLY starts, the monsoons of 2013 will be here and during the rainy season, we all know that major preventive work cannot really be done; all we can do then is fire fighting and emergency crisis management.
The monsoons were mild this year (which poses other problems as regards severe water shortage problems in the Mar-May2013) so we did not have major landslides in our area.

In an age where we should increasingly be expecting the unexpected, aren't we pushing our luck too far to for hope this trend to continue?

Praful Rao