Natural & Manmade Disasters

Natural and Manmade Disasters

Natural causes include:  Saturation of slope material from rainfall or seepage,  Vibrations caused by earthquakes,  volcanic eruptions, Or  undercutting of cliffs and banks by waves or rivers, Tsunami etc.

Human activities may include: The removal of vegetation,  interference with or changes to natural drainage,  Leaking pipes (water, sewer),  The modification of slopes by construction of roads, railways or buildings, mining activities,

 Vibrations from heavy traffic or blasting; and excavation or displacement of rocks.

Landslides A landslide is the movement of a mass of rock, debris or earth down a slope. All landslides have two things in common - they are the result of failure of the soil and rock materials that make up the hill slope and they are driven by gravity. They can vary in size from a single boulder in a rock fall or topple to tens of millions of cubic metres of material in a debris avalanche. Landslides can be triggered by natural causes or by human activity.

Date/year

Location

Damage

January 1982

Nashri, Jammu & Kashmir

Active slide from 1953. Every year road and communication network is damaged.

March 1989

Himachal Pradesh

Nathpa, 500m road section is frequently damaged during successive year

October 1990

Nilgris

36 people killed and several injured. Several buildings and communication network damaged

July 1991

Assam

300 people killed, road and buildings damaged, Millions of rupees

November 1992

Nilgiris

Road network and buildings damaged, Rs.5 million damage estimate

June 1993

Aizawal

Four persons were buried

July 1993

Itanagar Arunachal Pradesh

25 people buried alive 2 km road damaged

August 1993

Kalimpong, West Bengal

40 people killed, heavy loss of property

August 1993

Kohima, Nagaland

200 houses destroyed, 500 people died, about5km road stretch was damaged

November 1993

Nilgris

40 people killed, property worth several lakhs damaged

January 1994

Kashmir

National Highway 1A severely damaged

June 1994

Varundh ghat, Konkan Coast

20 people killed, breaching of ghat road damaged to the extent of 1km. At several places

May 1995

Aizwal Mizoram

25 people killed road severely damaged

June 1995

Malori Jammu

6 persons killed, NH 1A damaged

September 1995

Kullu, HP

22 persons killed and several injured about 1 km road destroyed

14,August 1998

Okhimath

69 people killed

Incidences of Landslides in India

Region

Incidences of Landslides

Himalayas

High to very high

North-eastern Hills

High

Western Ghats and the Nilgiris

Modern to high

Cattle lost

Low

Vindhayachal

Low

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:

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Slope-Magnitude, length and Direction

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Soil thickness

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Relative relief

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Land use

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Drainage- pattern and density

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Landslide affected population

Landslide types Once a landslide is triggered along a plane of weakness, material is transported by various mechanisms including sliding, flowing or falling.

The rate of landslide movement varies from extremely slow in landslides moving at only millimetres to centimetres per year to a sudden and extremely rapid (metres per second) avalanche of debris. Sudden and rapid events are the most dangerous because of the lack of warning, and the speed at which they can travel down the slope and the force of impact. Distance travelled by landslide material, varies greatly, from a few centimetres to many kilometres depending on the volumes of debris, mud and water flow going down river valleys.

Common landslide types SLIDE

CREEP

SLUMP

TOPPLE

FALL

FLOW

What causes a flood? A number of factors can contribute to that imbalance, including: Heavy, intense rainfall Run-off from a deep snow cover Over-saturated soil, when the ground can't hold anymore water. Frozen soil High river, stream or reservoir levels caused by unusually large amounts of rain Ice jams in rivers Urbanization, or lots of buildings and parking lots There are two basic types of floods. In a regular river flood, water slowly climbs over the edges of a river. The more dangerous type, a flash flood, occurs when a wall of water quickly sweeps over an area.

Floods depend on many things such as Climate, nature of the Collecting basin, nature of the streams, soil, vegetative cover, amount of snow melt and over all rainfall. Annually, the Indian land mass receives on precipitation of 88-89 cm with very high variation from region to region. In the state of Rajasthan, the rainfall is almost nil whereas in the state of Meghalaya, an average rainfall of 1000 cm occurred every year. So this variation in the occurrence of rainfall makes the country prone towards the situations like floods and droughts

Floods

Effects of floods The effect of a flood can be catastrophic. All these things can happen: -Broken roads and railway lines. -Damage to furniture and objects in houses. -Wrecked houses. -Crushed crops. -The electricity and gas supplies are cut off. -Diseases. -People and animals are killed. -Ornaments can be smashed. -Electrical items like computers and TV's can be damaged. -Carpets start to disintegrate. -Property gets washed away. -Trees fall over. -Cars get smashed. -Bridges break.

Sandbags to protect property

 

Raising banks before a flood

                                              wall Flood

A floodway

Tsunami 

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What is a tsunami? A tsunami is a series of waves with a long wavelength and period (time between crests). Time between crests of the wave can vary from a few minutes to over an hour. Tsunamis are often incorrectly called tidal waves; they have no relation to the daily ocean tides. Tsunami (soo-NAH-mee) is a Japanese word meaning harbour wave. Tsunamis can occur at any time of day or night.

How are tsunamis generated? • Tsunamis are generated by any large, impulsive displacement of the sea bed level(Fig.1). • Earthquakes generate tsunamis by vertical movement of the sea floor. If the sea floor movement is horizontal, a tsunami is not generated. Earthquakes of M > 6.5 are critical for tsunami generation. • Tsunamis are also triggered by landslides into or under the water surface, and can be generated by volcanic activity and meteorite impacts. 

As waves approach shore formation on shore they slow down, the waves lengths shorten and become higher

Tsunami wave train formation

Submarine fault movement, landslide or Volcanic activity

Wave train of Tsunami

 How

often do tsunamis occur? • On the average, there are two tsunamis per year somewhere in the world which cause damage near the source. • Approximately every 15 years a destructive, Pacific-wide tsunami occurs. • The destructive tsunami on Dec 26th, 2004 on the Indian Coast seems to have occurred for the first time in the history.

Indian Ocean Tsunami of Dec.26th, 2004

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How big is a tsunami? Tsunamis range in size from centimeters to over 30 m height. Most tsunamis are less than 3 m in height. In deep water (greater than 200 m), tsunamis are rarely over 1m high and will not be noticed by ships due to their long period (time between crests). As tsunamis propagate into shallow water, the wave height can increase by over 10 times. Tsunami heights can vary greatly along a coast. The waves are amplified by certain shoreline and bathymetric (sea floor) features. A large tsunami can flood land up to more than 1.5 km from the coast. The force of some tsunamis is enormous. Large rocks weighing several tons along with boats and other debris can be moved inland hundreds of feet by tsunami wave activity. Homes and other buildings are destroyed. All this material and

Protection from Risk of Tsunami • Know the height of your street above sea level and the distance of your street from the coast or other high-risk waters. Evacuation orders may be based on these numbers. Also find out the height above sea level and the distance from the coast of outbuildings that house animals, as well as pastures or corrals. • Use a Weather Radio or stay tuned to a local radio or television station to keep informed of local watches and warnings. • You should avoid building or living in buildings within 200 meters of the high tide coastline. These areas are more likely to experience damage from tsunamis, strong winds, or coastal storms. • Have an engineer check your home and advise about ways to make it more resistant to tsunami water. There may be ways to divert waves away from your property. Improperly built walls could make your situation worse. Consult with a