Landslides

slidesLand

Made by :- Aditya JulkaAndParitosh

A landslide is a geological phenomenon which includes a wide range of ground movement, such as rock falls, deep failure of slopes and shallow debris flows, which can occur in offshore, coastal and onshore environments. Although the action of gravity is the primary driving force for a landslide to occur, there are other contributing factors affecting the original slope stability. Typically, pre-conditional factors build up specific sub-surface conditions that make the area/slope prone to failure, whereas the actual landslide often requires a trigger before being released.

Large block known as a slump block moves during the landslide.

The scar above a landslide is easily visible.

They can occur along a slope where the internal resistance of the rocks are reduced or they loose their holding capacity.

Common after earthquakes or after removal of part of the slope due to construction, particularly for construction of roads.

During the movement landslide can result into the Debris slides - are failure of unconsolidated material on a surface; Rock slide or Rock Fall – where movement of large rock block rolls

They are also common along the steep banks of rivers, lakes etc.

Pore Water Pressure is the key to monitoring landslides. Shear strength (a resisting force) decreases and the weight (a driving force increases).

Talus – accumulation formed by the coarser rock fragments resulted from the mechanical weathering along a slope under influence of gravity

Landslides occur when the stability of a slope changes from a stable to an unstable condition. A change in the stability of a slope can be caused by a number of factors, acting together or alone. Natural causes of landslides include:

groundwater pressure acting to destabilize the slope Loss or absence of vertical vegetative structure, soil

nutrients, and soil structure (e.g. after a wildfire) erosion of the toe of a slope by rivers or ocean waves weakening of a slope through saturation by

snowmelt, glaciers melting, or heavy rains earthquakes adding loads to barely-stable slope earthquake-caused liquefaction destabilizing slopes volcanic eruptions

landslides are aggravated by human activities, Human causes include: deforestation, cultivation and construction, which destabilize the already fragile slopes

vibrations from machinery or traffic blasting earthwork which alters the shape of a slope, or

which imposes new loads on an existing slope in shallow soils, the removal of deep-

rooted vegetation that binds colluviums to bedrock

Construction, agricultural or forestry activities (logging) which change the amount of water which infiltrates the soil.

Landslide hazard analysis and mapping can provide useful information for catastrophic loss reduction, and assist in the development of guidelines for sustainable land use planning. The analysis is used to identify the factors that are related to landslides, estimate the relative contribution of factors causing slope failures, establish a relation between the factors and landslides, and to predict the landslide hazard in the future based on such a relationship. The factors that have been used for landslide hazard analysis can usually be grouped into geomorphology, geology, land use/land cover, and hydrogeology. Since many factors are considered for landslide hazard mapping, GIS is an appropriate tool because it has functions of collection, storage, manipulation, display, and analysis of large amounts of spatially referenced data which can be handled fast and effectively.Remote sensing techniques are also highly employed for landslide hazard assessment and analysis. Before and after aerial photographs and satellite imagery are used to gather landslide characteristics, like distribution and classification, and factors like slope, lithology, and land use/land cover to be used to help predict future events. Before and after imagery also helps to reveal how the landscape changed after an event, what may have triggered the landslide, and shows the process of regeneration and recovery.

Using satellite imagery in combination with GIS and on-the-ground studies, it is possible to generate maps of likely occurrences of future landslides. Such maps should show the locations of previous events as well as clearly indicate the probable locations of future events. In general, to predict landslides, one must assume that their occurrence is determined by certain geologic factors, and that future landslides will occur under the same conditions as past events. Therefore, it is necessary to establish a relationship between the geomorphologic conditions in which the past events took place and the expected future conditions.

Natural disasters are a dramatic example of people living in conflict with the environment. Early predictions and warnings are essential for the reduction of property damage and loss of life. Because landslides occur frequently and can represent some of the most destructive forces on earth, it is imperative to have a good understanding as to what causes them and how people can either help prevent them from occurring or simply avoid them when they do occur. Sustainable land management and development is an essential key to reducing the negative impacts felt by landslides.

GIS offers a superior method for landslide analysis because it allows one to capture, store, manipulate, analyze, and display large amounts of data quickly and effectively. Because so many variables are involved, it is important to be able to overlay the many layers of data to develop a full and accurate portrayal of what is taking place on the Earth's surface. Researchers need to know which variables are the most important factors that trigger landslides in any given location. Using GIS, extremely detailed maps can be generated to show past events and likely future events which have the potential to save lives, property, and money.

Rhine cutting through Flims Rockslide debris, Switzerland

Landslide which moved Heart Mountain to its current location, the largest ever discovered on land. In the 48 million years since the slide occurred, erosion has removed most of the portion of the slide.

Flims Rockslide, ca. 13,000 km3 (3,100 cu mi), Switzerland, some 10000 years ago in post-glacial Pleistocene/Holocene, the largest so far described in the alps and on dry land that can be easily identified in a modestly eroded state.

The landslide around 200BC which formed Lake Waikaremoana on the North Island of New Zealand, where a large block of the Ngamoko Range slid and dammed a gorge of Waikaretaheke River, forming a natural reservoir up to 248 metres deep.

Cheekye Fan, British Columbia, Canada, ca. 25 km2 (9.7 sq mi), Late Pleistocene in age.

Date Place name Casualties comments

9 November 2001

Amboori, Kerala, India 40 deadSupposedly worst landslide in Kerala state's history.

26 March 2004

Mount Bawakaraeng,South Sulawesi,Indonesia

32 dead Landslide caused by collapse of caldera wall

10 January 2005

La Conchita, California,United States2005 La Conchita Landslide

10 deadRemobilization of colluvium from 1995 slide into a debris flow.

17 February 2006

Southern Leyte,Philippines 2006 Southern Leyte mudslide

1,126Rock-debris avalanche triggered by ten day period of heavy rain

11 June 2007 Chittagong,Bangladesh2007 Chittagong mudslides

123+Series of landslides caused by illegal hillside cutting and monsoon rains

6 September 2008

Cairo, Egypt 2008 Cairo landslide 119Rockfall from cliffs, individual boulders up to 70 tonnes

9 August 2009

Xiaolin (or Hsiao-Lin),Kaohsiung County,Taiwan

439 to 600

4 January 2010

Attabad, Gilgit-Baltistan, PakistanHunza Valley Landslide

20Formed Attabad Lake by dammingHunza River, blocked Karakoram Highway

1 March 2010

Bududa District,Uganda2010 Ugandan landslide

100-300 dead

23 May 2010

Jiang Zhidong Jiangxi, China2010 Jiangxi train derailment

The landslide was caused by previous days of heavy rain and flooding in the region.

10 May 2010

Saint-Jude, Quebec 4 dead

6 August 2010

Meager Creek, British Columbia, Canada

Second-largest landslide in Canada history

August 8, 2010

Gansu, ChinaZhouqu county mudslide

1287 killed and 457 missing

Landslide mitigation refers to lessen the effect of landslides by constructing various man made projects at the slopes which are vulnerable to landslides planning for landslides hazard mitigation as its phenomenon is instant. Landslides can be triggered by many often concomitant causes. In addition to shallow erosion or reduction of sheer strength caused by seasonal rainfall, causes triggered by anthropic activities such as adding excessive weight above the slope, digging at mid-slope or at the foot of the slope, can also be included. However, often individual phenomena join together to generate instability, also after some time has elapsed, which, other than in well-instrumented limited areas, do not allow a reconstruction of the evolution of the occurred landslide. It is therefore pointless, for the purpose of planning landslide hazard mitigation measures, to classify the work as a function of the phenomenon or of more important phenomena, renouncing any attempt to precisely describe all the causes or the conditions which, at different times, contribute to the occurrence of the landslide. Therefore, slope stabilisation methods in rock or in earth, can be collocated into three types of measure:

Geometric methods, in which the geometry of the Geometric methods, in which the geometry of the hillside is changed (in general the slope);hillside is changed (in general the slope);

Hydrogeological methods, in which an attempt is Hydrogeological methods, in which an attempt is made to lower the groundwater level or to reduce made to lower the groundwater level or to reduce the water content of the material;the water content of the material;

Chemical and mechanical methods, in which Chemical and mechanical methods, in which attempts are made to increase the shear strength attempts are made to increase the shear strength of the unstable mass or to introduce active external of the unstable mass or to introduce active external forces (e.g. anchors, rock or ground nailing) or forces (e.g. anchors, rock or ground nailing) or passive (e.g. structural wells, piles or reinforced passive (e.g. structural wells, piles or reinforced ground) to contrast the destabilising forces.ground) to contrast the destabilising forces.

The different type of material conditions the The different type of material conditions the

engineering solution adopted, although It always engineering solution adopted, although It always comes back, in principle, to the previously comes back, in principle, to the previously introduced classification.introduced classification.