Danger in the hills of Ranchi district in Jharkhand State of India.

 

Hills are becoming vulnerable to major land slides in future.

by 

Dr. Nitish Priyadarshi

Geologist and Assistant Professor,

Department of Geology,

Ranchi University,

India.

Below are the photographs of the hills around Ranchi the capital city of Jharkhand state of India. During my recent visit to these hills  in Patratu valley and Angada block  I saw some of the areas which are vulnerable to major land slides in coming future. 

 

 

 

Most of the hills are highly weathered. They are steep-sided residual hills made of massive granite-gneiss. Few hills especially in Angada block and Patratu valley near Ranchi are showing the trend of landslides. Many slopes are already in delicate equilibrium and slight increase in rainfall and human interference may trigger the land slides under the influence of gravity. The flow of the Nalkari river, the tributary of Damodar river, can get blocked due to possible land slide in the Patratu valley . Nalkari river contributes water to the Patratu Dam. Excessive precipitation are the frequent cause for landslides which weakens the slope materials. Other factors that weaken slope materials also contribute to the occurrence of landslides. Ranchi receives 1200 to 1600 mm annual rainfall.  Most of the hills are having steeper slopes so they are more exposed to rapid erosion than the gentler ones.   Many hills of the Ranchi plateau are highly susceptible to slope instability due to the immature and rugged topography, fragile rock conditions, and high rainfall.

The Ranchi Plateau, composed mostly of gneisses and granites, is about 2000 ft. above sea level. The topography is roughly undulating with terraced slopes ending on the one hand on the banks of a local stream and on the other in local upland which may or may not have a low hill, or which may or may not consist of solid rocks exposed bare soils.

The present topographic features of Chotanagpur  ( Ranchi plateau) are a clue to the past and geologists think that before the Himalayan movement started in Tertiary times Chotanagpur and adjoining areas were a low peneplain. As a side-effects of the violent Himalayan movements, parts of peninsular upland in general and Chotanagpur peneplain in particular began to be successively uplifted. The Himalayan movements occurred three times during Early and Late Tertiary and Pleistocene times and probably the Chotanagpur peneplain was also concurrently subjected to three successive uplifts.  

Landslides occur when the slope (or a portion of it) undergoes some processes that change its condition from stable to unstable. This is essentially due to a decrease in the shear strength of the slope material, to an increase in the shear stress borne by the material, or to a combination of the two. A change in the stability of a slope can be caused by a number of factors, acting together or alone.

Landslides can be initiated in slopes already on the verge of movement by rainfall, snowmelt, changes in water level, stream erosion, changes in ground water, earthquakes, volcanic activity, disturbance by human activities, or any combination of these factors.

Causes of landslides in Ranchi plateau include:

1.     Saturation by rain water infiltration.

2.     Increase of pore water pressure by rain water infiltration.

3.     Increase of hydrostatic pressure in cracks and fractures.

4.     Physical and chemical weathering.

5.     Deforestation, cultivation and construction.

6.     Blasting and mining.

7.     Erosion by river flows.

Beware of the hills.

Frequency of landslides in India is indeed increasing. 

By

Dr. Nitish Priyadarshi

Geologist.

Malin, the village in Pune district that was flattened by a landslide few days back claiming more than 130 lives, has brought the focus back on the management –or mismanagement – of the vulnerable hills of India especially Western Ghats, Himalayas and North Eastern states.

The torrential rain on July 30 near Pune perhaps would not have brought down a side of the hill had it not been weakened by quarrying, leveling and deforestation activities banned in the old weathered hills and ecologically sensitive areas.

Last year it was Uttrakhand this year it is Malin and Nepal. A massive landslide in Nepal  triggered by continuous monsoon rains, caused 10 deaths, displaced 5,000 families and destroyed dozens of houses. The landslide has also blocked the Sunkoshi River and forming a lake which is threatening to cause downstream flash floods.

Heavy rainfall in June last year wreaked havoc across Uttarakhand, causing rivers and glacial lakes to overflow and triggering massive landslides – killing almost 6,000 people. Construction of hydroelectric dams, deforestation and the spread of unregulated buildings along riverbanks magnify the impact of the monsoons.

Development works carried out in pursuit of greater economic growth – such as the construction of dams and deforestation – are putting people and the environment at greater risk when disasters strike.
India is one of the most disaster-prone countries in the world, and many of its 1.2 billion people live in areas vulnerable to natural hazards such as floods, landslides, cyclones, droughts and earthquakes.

Landslides are a natural hazard that affect at least 15 percent of the land area of our country, covering an area of more than 0.49 million sq. km. landslides of different types occur frequently in the geo-dynamically active domains in the Himalayan and North-Eastern parts of the country as well as relatively stable domain in the Western Ghats and Nilgiri hills in the southern part of the country. Besides, sporadic occurrences of landslides have been reported in the Eastern Ghats, Ranchi plateau, and Vindhyan plateau, as well. In all 22 states and parts of the Union Territory of Pudducherry and Andaman and Nicobar Islands of our country are affected by this hazard, mostly during monsoons.

Landslides Zonation Mopping is a modern method to identify landslides prone areas and has been in use in India since 1980s.The major parameters that call for evaluation are as follows:

1. Slope-Magnitude, length and Direction
2. Soil thickness
3. Relative relief
4. Land use
5. Drainage- pattern and density
6. Landslide affected population

Causes of Landslides

Landslides can be caused by
1. Poor ground conditions
2. Geomorphic phenomena.
3. Natural physical forces
4. Quite often due to heavy spells of rainfall coupled with impeded drainage.

A Checklist of Causes of Landslides Ground Causes

1. Weak, sensitivity, or weathered materials
2. Adverse ground structure (joints, fissures etc.)
3. Physical property variation (permeability, plasticity etc)

The Himalayan mountain ranges and hilly tracts of the North-Eastern region are highly susceptible to slope instability due to the immature and rugged topography, fragile rock conditions, high seismicity resulting from proximity to the plate margins and high rainfall. Extensive anthropogenic interference, as part of developmental activities, is another significant factor that increases this hazard manifold. As a result, the landscape in the Himalayan and North-Eastern regions is highly susceptible to reoccurrence of landslides.

Similarly, the Western Ghats overlooking the Konkan coast, though located in a relatively stable domain, experience the fury of this natural hazard due to steep hill slopes, overburden and high intensity rainfall. The Nilgiri hills located at the convergence zone of the Eastern Ghats and the Western Ghats bear the innumerable scars of landslides due to their location in a zone of high intensity and protracted rainfall where overburden is sensitive to over-saturation.

Vast areas of western Sikkim, Kumaon, Garhwal, Himachal Pradesh, Kashmir, and several other hilly regions have been denuded of protective vegetal cover, which has been reduced to less than 30 percent, which is less than half of what would be considered desirable. As the pressure of population grew rapidly, more and more human settlements, roads, dams, tunnels, water reservoirs, towers and other public utilities came up in vulnerable areas. The road network in the Himalayan region is more than 50,000 km in length. A large number of dams have been built in the Himalayan region. Quarrying and mining, for example, in the Doon valley, Jhiroli (Almora) and Chandhak (Pitthoragarh) have inflicted heavy damages to the slopes and the associated environment.

According to the information obtained under RTI, In Mumbai city over 22,483 hutment in 327 hilly areas across 25 Assembly constituencies in the city, including Western and Eastern suburbs, are dangerous and the people living there need to be shifted as soon as possible. In the main city, 49 spots are dangerous in which total hutments are 3986, while in Mumbai Suburb 278 spots are most dangerous.

An overall evaluation of the pattern and nature of landslide occurrences in the Kerala part of Western Ghats and its corresponding eastern flank falling within Tamil Nadu reveals the following main features:

1.      Almost all mass movements occur during monsoons (SW and NE monsoon) in the western flank of Western Ghats and during occasional cyclonic events in the eastern flank indicating that main triggering mechanism is the over- saturation of overburden caused by heavy rains.

2.      There seems to be a relation between intensity of rainfall and slope failures.

3.      Majority of the catastrophic mass movements is confined to the overburden without affecting the underlying bedrock.

4.      Improper land use practices such as heavy tilling, agricultural practices and settlement patterns have contributed to creep and withdrawal of toe support in many cases.

5.      A common factor noticed in most of these vulnerable slopes deforestation in the recent past, cultivation of seasonal crops and increase in settlements.

6.      In some areas developmental activities like construction of buildings, road cutting, embankments, cut and fill structures causes modification of natural slopes, blocking of surface drainage, loading of critical slopes and withdrawal to toe support promoting vulnerability of critical slopes.

Frequency of landslides is indeed increasing. The main reasons for this are primarily unplanned development in landslide prone areas which can change the geomorphology of that area. Because of accelerated deforestation, rampant urbanization, high frequency of earthquakes, fragile geological structures, steep topography and intense rainfall in the mountainous regions of the South Asia, the number of fatal landslides, casualties and economic loss is increasing year by year. Increasing extreme events due to climate change are also responsible for this phenomenon. Rainfall is becoming extreme in India, either heavy or scanty. If there is a lot of rainfall in a short span of time, then the soil is not able to absorb the moisture, which makes it vulnerable to erosion and slope instability, eventually leading to landslides.

The Himalayan and North-Eastern regions are potential sites where landslides dams have formed at many places in the past and the potential of such occurrences in the future is high.

Reference:

National disaster management guidelines, June 2009. National disaster management authority, Government of India.

http://agritech.tnau.ac.in/agriculture/agri_majorareas_disastermgt_landslide.html

http://www.dnaindia.com/india/report-india-s-worst-landslides-and-why-these-might-not-be-the-last-ones-2006836

http://www.livemint.com/Politics/PWWZWaeFPN70bXKgh78i8K/All-you-need-to-know-about-landslides.html

 

Uttrakhand disaster in India is nature’s fury but consequences are man made.

A short film on causes and impact of disaster in Uttrakhand state in India.

By

Dr. Nitish Priyadarshi

Geologist. 

 

This was one of the most challenging disasters till date at Kedarnath so much so that even after few days also it was really tough for a human mind to calculate the loss. It made everyone busy. Media is covering as much as they can. Indian army, air force, navy all are focusing here to save the human lives. Still death is uncountable along with other losses.

Analysis differs. While the administration insists that it was a natural calamity, environmentalists hold that this was a man-made disaster waiting to happen.

Though it was nature’s fury but the after effects was purely man made. It happened because geology of the area was always neglected in construction and expansion of the affected areas. Observations suggest that inadequate consideration of geology and geomorphology during the road alignment and poor, faulty engineering techniques were major factors responsible for the recent landslides and disaster.

To make a hill road, you have cut through the hill. When you cut through an unstable hill, you are creating conditions for more landslides that are a natural and frequent phenomenon. Several hydropower projects and mining projects are going on in Uttarakand. The blasts along the fault lines, weathered, jointed and fractured  rocks during tunnel constructions or mining is leading to landslides.

The debris raises the water level in the river which leads to flash floods when it rains heavily. During monsoon such floods have become very common and cause a lot of destruction. A large number of trees are also cut for these projects, causing soil erosion and leading to massive landslides.

More than 220 power and mining projects are running in 14 river valleys in Uttarakhand. Several rivers are being diverted through tunnels for these projects leading to major disasters in the state.

Hill slopes in the Himalaya are known for their instability due to ongoing tectonic activity. However, increasing anthropogenic intervention in the recent times appears to be contributing to terrain  instability in addition to natural factors, as observed by increasing frequency and magnitude of landslides since 1970. In July, 1970 — Cloudburst in the upper catchment area led to a 15 metre rise in the Alaknanda river in Uttarakhand. Entire river basin, from Hanumanchatti near the pilgrimage town of Badrinath to Haridwar was affected. An entire village was swept away.

During August and September 2010, Uttarakhand Himalaya witnessed large-scale slope destabilization, particularly along the roads where widening work was in progress. The land-slides killed about 220 people in the en-tire rainy season of 2010.

The tectonic fault lines, which are active and see back-and-forth movements, have been cut in many places by roads. More dangerously, roads are built along the fault lines at many places. As a result, tiny seismic movements in the fault lines weaken the rocks at the base of the roads, making these stretches susceptible to cave-ins and slides.

Buildings have been constructed over flood ways, old drains and streams, blocking the natural pathways of rainwater. It’s also true that once river is flooded it will again be flooded in coming 100 years. People and local administration neglected this theory in ongoing constructions on the old flood ways. Other reason for the devastation at Kedarnath was that people had constructed houses on the west stream of the Mandakini river that had been dry for decades. When the river returned to its old course following the deluge, these constructions were washed away.

This area is characterized by different types of rocks, undulating terrain, and cool climate.

The removal of the forest cover has accelerated the rate of erosion and mass wastings in the area. Steeper slopes, high relative relief and presence of weathered, fractured/sheared rocks in addition to unfavourable hydrological conditions are characteristic features of the area. A number of landslide zones are observed in the area. Debris flows, rockfalls, toppling failures and ground subsidence are frequently observed. Every year, a number of landslides cause heavy damage to life and property.

Very high hazard zone has already been identified by geologists near Kedardome, Bhartiyakunta peak, Brahma Gupha, Salya, Devangan and Gaurikund in Uttrakhand State. Medium hazard zones are mostly present around Okhimath, Guptkashi, Kalimath and Rambara areas.

Maximum numbers of landslides after cloud burst have been observed to occur within a distance of one km on either side of the tectonic planes. Some major fault zones in Uttrakhand are Rawanganga fault, Madhyamahashwar fault, Mandakni fault, Godwanala fault and Kaldungnala fault along which a number of landslides occur. It has been indicated that a maximum frequency of landslides occurs along Madhyamahashwar, Godwanala and Rawanganga faults. Such areas must be taken into consideration before any constructions.

Such disasters have both short-term and long term impact on society and the environment. The short-term impact accounts for loss of life and property at the site and the long term impact includes changes in the landscape that can be permanent, including the loss of hills, cultivable land and the environmental impact in terms of erosion and soil loss, population shift and relocation of populations and establishments.

The frequent obstructions caused to the movement of traffic by numerous landslides during the rainy season, sometimes for days together, particularly in the Himalayan and North Eastern regions of the country, bring untold misery to the people inhabiting the villages and townships in the landslide-prone hilly regions.  

250 feet high hill collapsed overnight near Ranchi city of India.

Most of the hills in Jharkhand State are highly weathered.

by

Dr. Nitish Priyadarshi

Fig. Villagers praying the mountain under fear.,

On 8^th October in local news paper one news baffled me. The news stated that a 250 feet high hill vanished in thin air overnight. The incident happened some 50kms away from the Ranchi city, the capital of Jharkhand State of India. Being a geologist I have never heard about such phenomenon of vanishing hills suddenly in recent years or in past especially in Jharkhand State which is free from major earthquakes and Volcanism. Volcanism promotes such types of subsidence. The crumbling of a section of the huge ‘Jumbla’ Mountain Range in the Angara Circle of Ranchi district has posed a question mark on vanishing of 250 feet High Mountain. But the incident has occurred, so I decided to collect the information from different sources and media persons who visited the area.

The on-the-spot survey by some of the electronic media person revealed that the mountain section in question had not vanished but definitely caved in.

According to the reports reaching to me, the debris of the said section of the huge mountain range, in form of huge boulders and scattered pieces of rocks in a vicinity of nearly a kilometer from the peak were strewn. The sleepy village of Rasujara had a night-marish night on the 6^th of October when the entire village heard the hair raising thunders of rocks rumbling with heavy drizzle orchestrating it.

In the worst of their dreams they did not anticipate the scenario of the next morning. The very mountain which acted as their savoir had ‘vanished’ with scattered debris in its place! The small village of Rasujara with a population of less than 200 people was in a state of panic, thinking that the celestial forces were ‘angry’.

But before moving into any conclusion we should understand the rock types and geology of such hills in and around Ranchi district.

Most of the hills in the area has attained old age and are highly weathered. These hills are one of the oldest part of the earth’s crust. All the slopes below the top consists of soil, sediments and rock fragments. Occasionally there are few rock exposures.

Collapse of the hill may be due to weathering aided by mass-wasting forming ‘talus slopes’.

Mass wasting, also known as slope movement or mass movement, is the geomorphic process by which soil, regolith, and rock move downslope under the force of gravity. Types of mass wasting include creep, slides, flows, topples, and falls, each with its own characteristic features, and taking place over timescales from seconds to years.

Mass wasting may occur at a very slow rate, particularly in areas that are very dry or those areas that receive sufficient rainfall such that vegetation has stabilised the surface. It may also occur at very high speed, such as in rock slides or landslides, with disastrous consequences, both immediate and delayed.

The predominant processes that degrade a rock slope depend largely on the regional climate (temperature, amount of rainfall, etc.) and also through Thermal stresses and Topographic stresses.

From first instance it looks that the hill became the culprit of Debris avalanches. Debris Avalanches are very high velocity flows of large volume mixtures of rock and regolith that result from complete collapse of a mountainous slope. They move down slope and then can travel for considerable distances along relatively gentle slopes.

Other theory which can be implemented here that hill may have collapsed due to underground mine fire in the nearby coalfields of Ramgarh and Gola areas. Underground hollow created by mine fire may have put stressed on the highly weathered hill.

What ever may be the cause but it is true that more incidence like this may happen in future especially in Ranchi city where one of the hill, popularly known as Ranchi Hill, has already threatened the local people last year as part of it was affected with landslides.

Some of the other hills are also affected as they are in regular threat by explosives used by the miners for making stone chips for building purposes.