Uttarakhand,
one of the newly formed states of India is poised for of growth and
development. Development of road communication is one of the important
needs for faster transport of people and produce. Cutting a road means
destabilizing the mountain slopes.
The Himalayas as we know are a product of a great collision between the
Indian and the Asian plates some 20 million years ago. The mountains
that rose are still in the process of rising as the Indian Plate
continues to go forward under the Asian Plate. The material on mountain
slopes normally lies in a state of balance. The moment there is an
upheaval it triggers a chain of events and the slope forming material
begins to slide down due to gravity. Similarly all construction
activities like road building, housing, schools, hospitals etc
destabilize the slopes. Rainwater acts as a lubricant in the event of a
landslide triggered during the monsoons. It makes greater volume of mass
wasting.
The material that slides down kills people in its wake, often blocking
the rivers, producing temporary dams. When such dams burst, flash floods
cause death and destruction downstream. Through these columns I have
often repeated that people are not killed by an earthquake. They either
get buried under their own house or are crushed under a landslide in the
mountainous regions triggered by the earthquake.
Landslides are part of the mountain eco-system. One can not wish them
away. But yes a thorough study can delineate areas that are hazardous
from the point of view of landslides. Geologists are putting in best of
their efforts to identify the causes and slopes in the Himalayas prone
to landslides. Recently S.P. Sati, Y.P. Sundriyal and G.S Rawat of H.N.
Bahuguna, Garhwal University, Srinagar, Uttarakhand and N. Juyal of
Physical research Laboratory (PRL), Ahmedabad carried out an interesting
study of some of the perennial slide prone areas. Their studies have
highlighted the reasons of slides and mitigation measures. It is worth
knowing especially for those involved with the development of such slide
prone areas.
It is an established fact that the Indian Plate collided with the Asian
Plate, resulting in to major tectonic shape up. Due to this collision
some deep seated faults like the Main Central Thrust etc developed.
These thrust planes are now the weak planes along which the movements
are still on.
These thrusts are so powerful that they fracture and pulverize the
rocks. It is easy for water to seep in through such weakened rocks.
Swelled with water these rock masses are prone to slip. Once the process
sets in, there is no respite and landslides continue.
Role of forestry is important to hold such slopes. Alas we have
ourselves hacked forests to make beautiful houses. The dwellings thus
constructed are now prone for a sudden burial.
Spurt in earthquake occurrences in the past two decades in the Himalayas
is yet another factor that increases the frequency and magnitude of
landslides. Sati and his co-workers have found Remote Sensing and
Geographical Information System (GIS) useful for studying the slope
stabilities and also for planning development on more stable slopes. To
explain the utility of such studies they have taken four notorious
landslides, viz. Malpa, Garbayang, Okhimath and Budhakedar as a case
study.
Villages have sunk up to 20 m at
Garabayang.
Sati and his
colleagues report from Malpa that the village of the same name located
at the confluence of Malpa Gad and Kali River was buried under a
landslide due to continuous rains from 13th to 18th August 1998. They
ascribe the landslide to pore water pressure increasing due to rains,
which lead to movement of the hill side under the gravity. The slide
blocked the stream and blocked it. The dam burst and the flash floods
washed away whatever came in its wake.
The author was serving in the Geological Survey Of India (GSI) those
days and a team of two officers V.K. Sharma and R. Sanwal was
immediately dispatched to the site of disaster. It is worth recording
that the GSI's team was the first one to reach the site and collect
information. According to V.K. Sharma the higher reaches of Malpa Gad
have crystalline rocks. The open joints in these rocks were filled with
water. Night temperatures in the higher reaches drop to freezing levels,
especially during rains. Water in the joints and fissures of the rocks
there freezes at night. Same melts during the day. Melt water expands
and the process generates tremendous force to split open large chunks of
rocks.
Because of this reason Malpa has an old history of rock fall. The locals
were well aware of the problem and that is why the village and
habitation was away from the path of the rock fall. However, the Tourist
Reception Centre of the government was unfortunately situated in the
path of the rock fall. It is also worth mentioning that an Inspection
House of the Public Works department constructed during the British
regime is situated on a spur across Malpa Gad. The Inspection House
escaped the wrath of the falling boulders though its tin roof was
damaged by the smaller rocks which came like missiles from top. In this
tragedy 220 villagers, their houses and shops perished, due to the flash
floods.
While Sati and his colleagues have tried to blame the smaller faults
present in the area, Sharma says the landslide was mainly due to
nature's ire. He has strongly recommended use of precautionary measures
especially during the pilgrim rush for Kailash Mansarover pilgrimage.
The GSI team had reported that the rock fall had started on the night of
13th August itself and in fact a mule had succumbed to the rock fall.
Had precautions been taken, at least the pilgrims camping there on
return journey from Kailash could have been saved!
Garbayang, the prosperous village on the erstwhile Indo-Tibet trade
route is on the brink of extinction, as more than 80% of the inhabitants
have already migrated. Those who have remained there are so poor that
they can not afford to move out. This is a unique case of mass migration
in recent times. People have deserted their villages in Rajasthan due to
soil alkalinity forced on their fields by the Indira Gandhi Canal.
However, the Garbayang residents have been forced out by the Mother
Nature. Garbayang is a sinking village. Scientific reason for which is
location of the village over glacial lake sediments. Due to compaction
the plinths of the houses sink, causing wide, vertical cracks on the
walls. The phenomenon of sinking of the village was first noticed by S.P.
Nautiyal of GSI in 1948. In his report he had strongly recommended
relocation of the village. Unfortunately it was not implemented. The
sinking is unique because it is continuous and Sati and his friends have
recorded up to 20m of sinking in a span of ten years. Incidentally
Garbayang is just 12 km from the 'dreaded' Malpa.
Many times mythologies and folklores corroborate the geological facts.
As per the folklore there used to be a huge lake prior to the habitation
and thus land was scanty for the settlement. The locals prayed to their
local God Namjung to drain the lake. God acceded and broke the barrier
at Chiyalekh. This phenomenon has been confirmed by the geologists when
they found evidences of bursting of the terminal moraine barrier at
Chiyalekh.
Okhimath in Madhyamaheshwar valley also faced large scale death and
destruction due to heavy landslides. Okhimath has unique terraced fields
on the steep hill slope. Through a system of network of drains (locally
termed canals) water is taken from the upstream of the river to the
highest terrace from where it is allowed to trickle down to lower
reaches. Each field has a raised bank on the edge to hold water
especially for rice cultivation. And movement of water is controlled. It
was August 1998, the rice fields were already full up to the brim plus
the unprecedented rain made them full like water filled balloons. On the
higher reaches the crystalline rocks are covered by a dense Cedar
forest. These rocks have wide open joints and fractures because of the
sub-surface movements as they are in the vicinity of the MCT. Freezing
and thawing of water in these joints and fissures which are further
opened by the roots of the ancient trees is a common phenomenon. Thus on
the fateful night the rock mass along with the clay of the rice field
decided to slide down. So powerful was the landslide reported V.K.
Sharma of GSI that the material not only blocked the stream, part of it
damaged the houses on a higher elevation on the opposite side. Bhenti
village in Madhyamaheshwar valley was obliterated and Paundhar village
on the opposite bank suffered heavy casualties.
Composite picture of 1998 landslide at
Bhenti.
Okhimath has
been prone to such landslides since ages. But this time it cost 100
lives and property worth crores was destroyed. It is common observation
that an area so prone to landslides has become densely populated and
people have now constructed houses on areas hitherto considered unsafe.
Even at the time of investigation of the landslide by the team of GSI in
September 1998, a seven storey Hotel had come up at the Bus Stand of
Okhimath, located just below the vulnerable steep, fragile slope.
Similarly at Kimothi village houses have come close to the seasonal
streams.
Being located close to the MCT and with a set up which is ready to move
down the slope during monsoon, it is indeed hazardous to permit people
to live in such areas. It is an open invitation to tragedy. What the
local residents and even the administration failed to observe was that
the joints of the rocks at Bhenti village had become appreciably wide
after the 1991 Uttarkashi earthquake. The widening of joints and
fractures is a well established cause of landslides and slope failures.
Budhakedar in Bhilangana block of Tehri district witnessed widespread
landslides in an area of nearly 250 square km. These affected about 17
villages including Agunda, Medh, Marwari and Kot in Dharam Ganga valley
were almost wiped off by a cloud burst 10 August 2002. In general it was
a debris slide reported V.K. Sharma from GSI. Twenty-eight people lost
their lives in disaster. This area is prone to landslide is the common
observation of all the investigating agencies. Majority of the villages
affected are located on the stabilized debris of old landslides. The
fast flowing river with flanks denuded of vegetation due to
anthropogenic intervention makes the river cut its side rapidly. In
other words the 'toe' of the hill slopes is eroded. Naturally without
toe support the entire mass moves down aided by heavy rains.
The GSI team had strongly recommended relocation of villages above the
Highest Flood Level. In the event of a landslide the streams often get
blocked and when the blockade bursts there is a flash flood. Thus
locating habitation on safer ground should be the first move on part of
the government.
These were just few examples. There are hundreds of water
sheds/areas/villages that are helpless against the ire of the nature.
Urgent steps are needed to identify such areas and take remedial
measures before it is too late.
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