Department of Geology
University of Delhi
Delhi – 110 007
Landslides constitute one of the major damaging natural hazards in mountainous regions, triggered mainly under the influence of earthquakes and rainfall. These natural disasters have occurred in all part of Alborz range as well in central that is a highly populated area hilly area. The present paper focuses on the methodology for the Landslide Hazard Zonation and Risk analysis in part of central Alborz was carried out using Remote Sensing and Geographic Information System (GIS). that can be applied to same high relief terrain in all part of Alborz range. The zonation is based on information value method which has to designate in to five categories from High to low hazard zones. The methodology derived for the present studies has taken into consideration some well known factors in form of Various thematic layers like lithology, fault/lineament buffer, slope, morphology, slope aspect, soil, relief, drainage, landuse and incidence of landslides in the area were generated using remote sensing data and GIS tools. The main sources of the data for this study consists of different digital thematic maps and Arial photos and satellite imagery (IRS-IC , Lansat ETM and Rasarsat) . The Landslide Hazard Zonation have been accomplished in five stages according the base method arrangement Data Quantification, Calculation of Score Factor, Integration, Model Testing Zonation & Classification. A LHZ map was prepared showing the five zones, namely “very low hazard”, “low hazard”, “moderate hazard”, “high hazard” and “very high hazard”. The calculation and analysis of landside hazard zonation map over the GIS environment for risk assessment shows that Very high and High landslide hazard zones involves a 7.95 % of total population living over 37.60% of the total area with 14.9% of total settlements. Where the Low and very Landslide hazard zone cover 35 % of total area with 25.12 % of habitat and population of 40.39%
The Alborz range is an area with several geohazard (active deformation and faulting, landslide and rock falling) running along the southern side of the Caspian Sea. Central Alborz is highly populated region between eastern and western parts of Alborz that is surrounded by a set of strong active faults and landslide. Mass movement and rock falling are two main types of landslide hazards in this zone. Landslides coupled with earthquake in this high-risk area act as double disaster to villages, farmlands and roads as well the exacerbation of erosion of the land surface.
Detecting landslide and monitoring their activity using remote sensing are powerful methods to provide a wealth of information for assessing and mapping landslide hazards. The major advantages of using GIS in Landslide Hazard Zonation is the utilization of multiple datasets as layers and deciphers their importance for preparing hazard zonation maps and risk analysis.
This work incorporates investigation of landslide hazard assessment and risk analysis in part of central Alborz called Marzanabad. It is located in the Central Alborz at a distance of 30 km to Caspian Sea in the north and 100 km to the capital city of Tehran in the south. It covers an area of about 1048 sq km and is located between Latitudes 36° 15’00” N to 36° 35’00” N Longitudes 51° 07’30” E to 51° 27’30” E. ( fig 1)
Figure 1: location of area study in Iran and Central Alborz.
Geomorphology and geology setting
The study area is a cut by northeasterly flowing Chalous River forming a deeply incised valley called as Chalous valley. It is one of most important river in central Alborz that transfers water from dry area with annual precipitation less than 300 mm to the low land in south Caspian with annual precipitation above 1000mm The elevation of area decreases from south (4200m in Deewanh-A-Khu Mountain) to north (200m in runoff Chalous River) with a total length of 34 Km.(fig 2)
Figure 2 : True Color Composite, virtual 3D view, of Chalous valley facing south
The geomorphologic units have been enumerated on the basis of the processing of IRS 1D/1C -LISS III and Pan Imageries as well as interpretations of aerial photo mosaics. A DEM was generated and applied for extracting the geomorphologic features and morphometric analysis. This was further authenticated by field data collection and field checks. The important geomorphological parameters discussed are terrain mapping, drainage pattern, slope and aspect, soil, land use / land cover as input layer for landslide models (Fig 4 )
The investigated area, forming a part of the Alborz belt, has been subjected to repeated phases of tectonic movements which has resulted in a very complex geology The rocks of the this area are highly disturbed due to repeated folding faulting and thrusting.. (Clark et.al.1975; Seyed-Emami, 2003; Ghasemi-Nejad et.al., 2004; Fursich et.al.2005) The identification of different litho-units was carried out on the basis of two geological sheets at 1:100,000 scale namely Marzanabad and Chalous.(GSI, 2001 aerial photographs and Satellite Images.
Geological Survey of Iran have mapped the study area in)vA modified digital geological map of area has been prepared and discussed into different units as an input into landslide hazard studies based on the age of the rock formations, lithology, area of the unit and population in following table:
Table 1: geological information of study area
|Age||Formation||Main rock (lithology)||Area covered||Village/town located|
|Pro-Cambrian||kahar||Salty shale , sandstone , dolomite , quartzite||148.33||14.1||16||11.9||1007||2.2|
|Cambrian||Soltanieh||light dolomite , chert||53.64||5.1||1||0.7||84||0.2|
|Barut||siltstone and shale , cherty dolomite||8.80||0.8|
|Lalun||Red arkosic sandstone||19.77||1.9|
|Ordovician||Mila||Sandstone , shale , limestone , marl||2.08||0.2|
|Carboniferous||Mobarak||Black limestone , dolomitic limestone , marl||80.38||7.7||6||4.5||577||1.3|
|Permian||Dorud||Sandstone , shale , limestone, quartzite||26.93||2.6||3||2.2||50||0.1|
|Basic flows , pyroclastics , sandstone||0.99||0.1|
|Ruteh||Fusulina limestone , dolomitic limestone||43.97||4.2||2||1.5||138||0.3|
|Nesen||Cherty limestone , marly limestone , marl||3.88||0.4|
|Triassic||Elika||marly limestone , shale , quartzitic sandstone||2.77||0.3|
|Shamshak||Shale , sandstone , quartzite , conglomerate||179.45||17.1||30||22.4||6383||14.2|
|Jurassic||Lar||Limestone , dolomitic limestone||8.35||0.8||1||0.7||1140||2.5|
|Cretaceous||Tizkuh||Orbitolina limestone ( Apian – Cenomanian )||31.09||3.0||1||0.7||15||0.0|
|Chalous||Limestone ( Berriasian – Valanginian )||2.04||0.2||1||0.7||50||0.1|
|basalt , tuff breccias , pyroclastics , tuffite||41.58||4.0|
|basalt , conglomerate , tuff braccia , tuffs||71.05||6.8||15||11.2||1223||2.7|
|Globotruncana limestone , marly limestone||69.77||6.7||7||5.2||932||2.1|
|Marl , calcareous marl , marly limestone||51.11||4.9||7||5.2||719||1.6|
|Alternations of limestone and marl||33.06||3.2||5||3.7||412||0.9|
|Quaternary||terraces , colluviums , residual soils||105.08||10.0||33||24.6||29342||65.3|
In this study the major structures such as thrust and faults that have been considered as important parameters for the landslide hazard studies have been discussed. The area of investigation is traversed by number of thrust of regional extent, which generally shows NW-SE with northeasterly dips varying 30-59 degree. The various litho-units of area have been displaced by a number of faults. Most of these faults are transverse with reference of the thrusts.
Landsliding in the area
The landslide map of the area has been prepared in this study on the basis of arial photographs, satellite (Visible and Radar) and field investigations. The area has been subdivided into old landslide, active landslide; reactive landslides and rock falls.
Figure 4: (A) Landslide distribution map of the study area, (B) Arial photograph, 1955 of Valasht landslide, (C) 3D virtual view of Micher landslide
Method for Landslide hazard zonation:
Many methods have been proposed to evaluate landslde hazard spatially. Two approaches are the most promising: methods based on the statistical analysis of geo-environmental factors related to the occurrence of landslides; and deterministic modeling based on simple mechanical laws that control slope instability. (Guzzetti et al., 1999). The Information Value Based Method (Yin and Yan, 1988; Wu et al., 2000) has been selected for this research. This is the probabilistic approach based on the observed relationship between each factor and distribution and occurrence of the past and present landslides in the area of study.
The methodology derived for the present studies has taken into consideration some well known factors like lithology, fault/lineament, slope, morphology, slope aspect, soil, relief, drainage, landuse and incidence of landslides in the area.
Figure 4: methodology for landslide hazard zonation
Data preparing and landslide zonation:
The outcome of image processing is a set of thematic maps that are utilized as data inputs in different layers. The Geographic Information Science based data integration technique enabled us to analyze and interpret all these layers together for a Landslide Hazard zonation map.
The Landslide Hazard Zonation map have been accomplished in five stages
1- Data Quantification – all thematic maps were quantified and rasterised to specific pixel size (50m x 50m) Entire qualitative thematic information has been converted to quantitative data sets. A binary method was adopted for cross match of each parameter with respect to occurrence landslides map.
2-, Calculation of Score Factor- The score factor was calculated by determining susceptible factor of each variable for landslide failure.
3- Integration – all the influencing factors of different variables were simply added together to find out the probable areas of landslide occurrence.
4- Model Testing- primary result was tested for accuracy in the area of study.
5- Zonation & Classification – the whole range of variation was classified into five different groups of a Landslide Hazard Zonation map of the study area. (Fig 5)
Figure 5 : Landslide hazard map of the study area
The calculation and analysis of landside hazard zonation map over the GIS environment for risk assessment shows number of settlements and the population that falls under different classes of landslide hazard zones in relation to the number of persons at risk.
Table 2 : Landslide hazard in relation to no. of villages and population at risk in the area
|Landslide Hazard zone||Area on risk||Villages on risk||Population on risk|
|Very low landslide hazard zone||3.53||0.33||2||1.5||69||1.15|
|Low landslide hazard zone||137.73||13.13||33||24.62||17648||39.24|
|Moderate landslide hazard zone||532.90||50.82||79||58.95||23673||52.68|
|High landslide hazard zone||347.12||37.10||18||13.43||3360||7.47|
|Very high landslide hazard zone||27.15||2.58||2||1.5||215||0.48|
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