Quarrying in Landslide-Susceptible Areas in Kerala: Understanding Macro-scale Regional Landslide Susceptibility Mapping and Meso-scale Site-Specific Assessment

 By Biju Sebastian

 Introduction

Landslides are a major natural hazard in Kerala, particularly in the hilly regions where steep terrain, weathered rock, soil thickness, rainfall, drainage conditions and human interventions can influence slope stability. Quarrying in such areas therefore requires careful assessment of the terrain and the potential effects of quarry operations on slope stability.

Landslide Susceptibility Zonation (LSZ) maps are important tools for identifying areas that may be more susceptible to landslides. They help authorities and planners understand the regional distribution of landslide susceptibility and identify locations where more detailed investigation may be necessary.

However, a regional susceptibility map and a site-specific slope stability assessment serve different purposes. A map prepared at a regional scale cannot necessarily represent every geological, geomorphological and operational condition at an individual quarry. Consequently, the susceptibility category assigned to an area should not automatically be interpreted as a conclusive determination of the stability or instability of a particular quarry site.

The distinction between regional mapping and site-specific assessment is especially important when considering quarrying in areas classified as having high or moderate landslide susceptibility. The requirements set out in Annexure 24 of the Kerala State Disaster Management Plan provide a framework for more detailed investigation in specified circumstances.

This article explains the purpose and limitations of macro-scale landslide susceptibility mapping, examines the methodology adopted by the Geological Survey of India (GSI) in its Idukki study as a practical example, and discusses the role of meso-scale assessment and the implications of Annexure 24 for quarrying.

2.   Understanding Macro-Scale Landslide Susceptibility Mapping

Landslide susceptibility mapping is the process of identifying and classifying areas according to their relative likelihood of experiencing landslides, based on selected terrain, geological, geomorphological and environmental factors.

These factors may include slope gradient, slope-forming material, land use and land cover, aspect, regolith thickness, geomorphology and curvature. The importance of individual factors may vary according to the terrain, geological setting, available data and methodology adopted.

In a typical susceptibility-mapping exercise, the study area is divided into spatial units or raster cells. The selected factors are mapped, classified into categories and assigned ratings. Relative weights are then applied to the factors, and the weighted information is combined using a GIS-based method to derive a susceptibility index. The resulting index is classified into susceptibility zones, commonly described as High, Moderate and Low.

The final map provides a regional picture of relative susceptibility. It helps identify areas requiring closer attention, but it does not, by itself, establish the actual stability of every slope or the suitability of a particular quarry for operation.

Why does the scale of mapping matter?

The scale of a map influences the level of detail that can be represented and the extent to which local variations can be distinguished.

Macro-scale mapping provides a broad assessment over a relatively large geographical area. It is useful for regional planning, preliminary screening and identifying areas where further investigation may be warranted.

Meso-scale mapping and assessment examine a more limited area in greater detail. This permits closer examination of local terrain, geological structures, slope conditions, weathered material, drainage and other site-specific characteristics relevant to slope stability.

The distinction is important because conditions can vary considerably within the area represented by a single map category. A regional map may assign the same susceptibility class to a large area even though individual slopes within it differ in gradient, material, geological structure, drainage, vegetation and the extent of human modification.

Accordingly, the scale and purpose of a susceptibility map must be considered before using it to make decisions about an individual quarry.

How are susceptibility zones derived?

The methodology generally involves three principal steps:

1. Selection of factors: Terrain and environmental parameters considered relevant to landslide susceptibility are identified.

2. Assignment of ratings and weights: Individual classes within each factor are assigned ratings, and relative weights are applied to the factors.

3. Spatial combination and classification: The weighted factor layers are combined in a GIS environment to derive a susceptibility index, which is subsequently classified into susceptibility zones.

The ratings represent the relative contribution assigned to individual classes within a factor. The weights represent the relative importance assigned to the factors in the overall model.

The final susceptibility classification therefore depends on the factors selected, the ratings and weights adopted, the quality and resolution of the input data, the method of combining the layers, and the classification thresholds used.

To understand how these principles are applied in practice, the following section examines the macro-scale landslide susceptibility mapping study undertaken by GSI in Idukki district, Kerala.

Case Study: GSI’s National Landslide Susceptibility Mapping in Idukki, Kerala

Under the National Landslide Susceptibility Mapping (NLSM) programme, the Geological Survey of India (GSI) has undertaken landslide susceptibility mapping in different parts of Kerala. For the purpose of explaining the methodology adopted in macro-scale mapping, this article examines the study covering parts of Idukki district. Idukki is particularly relevant to this discussion because of its history of landslides and its significant exposure to landslide hazards. The Idukki study is therefore used as a case study to explain how the factors, class ratings and relative weights are incorporated into the preparation of a regional landslide susceptibility map.

The study was documented in the March 2021 report titled Macro-scale (1:50,000) Landslide Susceptibility Mapping in Parts of Toposheet Nos. 58G/1, 58G/2, 58G/5 and 58C/13 in Idukki District, Kerala.

This study provides a practical example for understanding how macro-scale landslide susceptibility mapping is carried out, including the selection of factors, assignment of class ratings and relative weights, and preparation of the final susceptibility zonation.

The report adopted an Analytical Hierarchy Process (AHP)-based weighted multi-class index overlay methodology in a Geographic Information System (GIS) environment. The following discussion examines the factors, ratings and weights used in the Idukki study to explain how the regional susceptibility classification was derived. These values are specific to the methodology adopted in the study and should not automatically be assumed to apply to every other region or quarry site.

GSI used seven factors in the Idukki model. The weights indicate the relative importance assigned to each factor in the overlay calculation. They are different from the ratings assigned to the individual classes within each factor.

Factor	Weight
Slope gradient	9
Land use/land cover (LULC)	8
Slope-forming material (SFM)	6
Slope aspect	5
Regolith thickness	4
Geomorphology	4
Curvature	2
Total	38

Slope gradient received the highest weight, followed by land use/land cover and slope-forming material. Curvature received the lowest weight. Consequently, a change in the rating of slope gradient has a greater influence on the composite score than an equivalent change in the rating of curvature. These weights represent the relative importance assigned within this particular model, not measured percentages of landslide causation.

Ratings assigned to the classes within each factor

Each factor was divided into classes, and each class was assigned a rating on a scale from 0 to 9. The following tables reproduce the ratings reported in the Idukki study.

1. Slope gradient

Slope gradient	Rating
Less than 15°	2
15°–25°	6
25°–35°	8
35°–45°	4
Greater than 45°	2

The highest rating was assigned to slopes between 25° and 35°. The rating decreases for slopes steeper than 35°. Thus, the model does not assume that susceptibility necessarily increases continuously with slope angle.

 2. Land use/land cover (LULC)

LULC class	Rating
Extensive slope cut	9
Settlement on modified slope	9
Moderate vegetation	6
Dumping ground	6
Plantation with low-height plants (LHP)	6
Sparse vegetation	4
Thick vegetation	4
Plantation with high-height plants (HHP)	4
Barren land	2
Quarry	2
Cultivation	2
Settlement	2
Fallow land	1
Water bodies and other listed classes	0

The LULC ratings are particularly relevant when interpreting susceptibility maps in areas affected by quarrying. The class “Quarry” received a rating of 2, whereas “Extensive slope cut” received 9 and “Dumping ground” received 6.

Quarrying, however, is not simply a land-use label. It can involve excavation of slopes, formation of benches and faces, removal of vegetation, accumulation or dumping of overburden, and other modifications to the natural terrain. Where these features are separately identified in the LULC mapping, they may influence the final susceptibility score through their respective ratings. Therefore, the low rating assigned to the class “Quarry” does not, by itself, establish that quarry-related terrain modifications have little influence on the final classification.

An additional question is whether all such features associated with existing quarries were identified and represented separately in the input maps. The rating table alone does not answer this question. Nor does it establish whether the mapped land use accurately reflected the condition of each quarry at the time of the underlying imagery and terrain data.

3. Slope-forming material (SFM)

Slope-forming material	Rating
Loose slide debris	8
Lithomarge	8
Colluvium	6
Weathered rock	4
Saprolite	4
Compact slide debris	3
Rock	2
In-situ soil, including lateritic soil	2
Transported soil	2

4. Slope aspect

Slope aspect indicates the direction towards which a slope faces.

Aspect class	Rating
NNE	1
NE	1
ENE	2
ESE	3
SE	5
SSE	6
SSW	9
SW	9
WSW	8
WNW	7
NW	4
NNW	2

The highest ratings were assigned to south-southwest-facing (SSW) and southwest-facing (SW) slopes, while north-northeast-facing (NNE) and northeast-facing (NE) slopes received the lowest ratings among the listed classes.

An important question is the basis for these differences. Were the ratings derived from observed landslide patterns, expert judgement, or a combination of available evidence?

The report indicates that an expert- or knowledge-driven approach was adopted because the available landslide inventory was insufficient for landslide-dependent spatial association analysis. AHP was used in assigning relative importance through expert assessment. However, the specific reasoning behind the high ratings for SSW and SW aspects is not evident from the rating table alone.

Aspect may influence local environmental conditions, but the ratings should not be interpreted as proof that southwest-facing slopes invariably have a higher landslide incidence. A clearer explanation of the basis for these ratings would help readers understand their applicability beyond the study area.

5. Regolith thickness

Regolith refers to the loose or weathered material overlying relatively intact rock.

Regolith thickness	Rating
Less than 0.5 m	0
0.5–5 m	6
5–10 m	5
Greater than 10 m	4

6. Geomorphology

Geomorphological class	Rating
Denudational slope	9
Fractured plateau edge	7
Moderately dissected slope	6
Transportational midslope	6
Waxing slope	6
Lowly dissected slope	5
Escarpment	4
Highly dissected slope	4
Mound	3
Rolling plain	2
Colluvial footslope	2
Waning slope	2
Valley, alluvial plain and other listed classes	0

 
7. Curvature

Curvature describes the shape of the terrain surface.

Curvature class	Rating
Concave	6
Flat	2
Convex	4

The weights and class ratings together form the numerical basis of the susceptibility model. The ratings reflect the relative influence attributed to the different classes, while the weights determine how strongly each factor contributes to the final score.

How the ratings and weights are combined

GSI adopted the weighted multi-class index overlay method described by Bonham-Carter (1994). For each pixel, the rating assigned to the applicable class of each factor is multiplied by that factor's weight. The weighted values are added and divided by the sum of the factor weights to obtain an average weighted susceptibility score.

Here, S is the susceptibility score for a pixel, F{ji} is the rating of the applicable class of factor i, and Wi is the weight assigned to that factor. Since the seven factor weights in this study total 38, the calculation can be expressed as:

The actual score depends on the class identified for each of the seven factors at the pixel under consideration. A high rating for one factor does not automatically make the pixel High susceptibility, because the other factor ratings and their weights also contribute to the result. Similarly, a low rating for one factor does not necessarily produce a Low susceptibility classification.

What do High, Moderate and Low zones mean?

A High susceptibility classification identifies terrain assessed as relatively more susceptible than terrain in the lower classes. A Moderate classification identifies an intermediate level of relative susceptibility, while a Low classification indicates relatively lower susceptibility within the mapped area.

The word Low must not be understood as no landslide possibility. Similarly, a High classification does not establish that a landslide will inevitably occur, or that every activity in the area must automatically be rejected. The classification is a regional screening result, not a site-specific engineering conclusion.

A 1:50,000 map also has limitations when applied to an individual quarry. The study used a 30-metre digital elevation model for certain terrain factors, and the final map represents terrain at a regional mapping scale. Local variations in rock joints, fractures, weathering, seepage, drainage, excavation geometry and other site conditions may not be adequately represented by the regional classification.

The ratings and weights in the study were based on expert judgement and the available information, rather than a sufficiently large dataset that would support a precise statistical prediction for every individual site. Consequently, the map should be used to identify areas that warrant further investigation—not as a stand-alone certificate of safety or a conclusive finding of danger.

This distinction is especially important for quarrying. Quarry operations can change the geometry of a hillside through excavation, bench formation and removal of material at the toe of a slope. Blasting, drainage alteration, storage of overburden and the placement of waste material may also affect stability. Those effects require assessment at the actual site.

From macro-scale mapping to meso-scale assessment

Macro-scale mapping and meso-scale assessment operate at different levels of detail.

The GSI macro-scale map at 1:50,000 provides a regional overview. It is useful for preliminary identification of susceptible areas, including the identification of High and Moderate zones relevant to the State’s quarrying guidelines.

A meso-scale assessment is more detailed and is intended to examine the terrain around a particular site. Annexure 24 refers to the GSI’s Standard Operating Procedure for Meso-Scale Landslide Susceptibility Mapping, which discusses mapping at 1:10,000 and 1:5,000 scales, with modifications specified in the Annexure. For the quarry-specific assessment required under Annexure 24, the susceptibility map must be prepared at 1:5,000 scale and cover the mining area and a 500-metre buffer around it.

The larger map scale permits more detailed representation of the local terrain and relevant features. The site-specific study can examine conditions that a regional map cannot adequately resolve, including local slope facets, exposed or partly exposed boulders, and the geological and geomorphological features relevant to the proposed excavation.

The difference is not merely one of cartographic presentation. The two mapping levels answer different questions:

• Macro scale: Which areas in the wider region are relatively susceptible and should receive further attention?
• Meso scale and site-specific investigation: What are the conditions at and around this quarry, how might the proposed operation affect slope stability, and what measures are necessary to manage the identified risks?

Thus, a High or Moderate classification in the macro-scale map is a screening trigger under the applicable guidelines. The detailed study is intended to provide the site-specific evidence needed for the subsequent decision.

Annexure 24 of the Kerala State Disaster Management Plan, updated 2026

Annexure 24 sets out guidelines for disaster-risk assessment and mitigation for mining activities in landslide-susceptible areas. It recognises that GSI’s Landslide Susceptibility Zonation maps, published through the State Disaster Management Authority’s channels, can be used for preliminary identification and assessment of susceptible areas. However, the regional maps alone are not sufficient to determine the actual landslide or rockslide susceptibility of a particular site, or whether quarrying would significantly increase that susceptibility.

The Annexure places emphasis on site-specific Slope Stability Assessment and Blast Vibration Assessment. Its stated approach is not simply to prohibit quarrying based on a regional colour classification, but to require scientific assessment, risk mitigation and consideration of the resulting recommendations before decisions are taken.

Which areas are covered?

The guidelines apply to quarrying activities in either of the following situations:

1. The quarry is operating or proposed in an area classified as High Hazard Zone or Moderate Hazard Zone in the GSI Landslide Susceptibility Zonation map.
2. The quarry is operating or proposed on a hill slope where a landslide has occurred in the past.

The second condition is important. Applicability is not determined solely by the colour shown on the macro-scale map. A previously landslide-affected hill slope may fall within the scope of the guidelines even if its regional map classification is not High or Moderate.

Conversely, the Annexure does not state that every quarry in a Low susceptibility zone automatically falls within its scope merely because it is a quarry. The previous-landslide condition and the other requirements of the guidelines must be considered.

The two mandatory site-specific studies

For quarrying activities falling within the scope of Annexure 24, two studies are prescribed.

Slope Stability Study

This study examines the stability of the slopes relevant to the proposed or existing quarry. Under the Annexure’s terms of reference, the assessment includes a susceptibility map at 1:5,000 scale for the mining area and its 500-metre buffer, together with the relevant thematic information. The study also addresses slope facets and boulders, including exposed or partly exposed boulders, and makes recommendations on matters such as overburden, rockfall and rockslide, storage of excavated material, hydrology and transportation of material.

Blast Vibration Study

The second study assesses the vibration effects of blasting and their implications for the quarry’s surroundings. The terms of reference address vibration measurements under different blasting conditions, the possible effects on cracks, joints and fractures, and the impacts on nearby residences, roads, infrastructure and landslide-prone slopes. They also require consideration of blast design, charge and delay arrangements, mitigation measures, and the feasibility of alternatives such as mechanical splitting.

The Annexure specifies NONEL as the approved blasting technique in the areas covered by these guidelines, subject to the stated conditions and supervision requirements. The prescribed assessment is intended to determine how blasting can be carried out while managing its potential effects on the surrounding terrain and structures.

Who must conduct the studies?

The quarry applicant must bear the cost of the studies. They must be undertaken through one of the institutions listed in Section 7 of Annexure 24: the National Institute of Rock Mechanics (NIRM); National Institute of Technology Karnataka (NITK), Surathkal; Indian Institute of Technology Roorkee; CSIR-Central Institute of Mining and Fuel Research (CIMFR), Dhanbad; National Institute of Technology Calicut; RITES Ltd.; CSIR-National Geophysical Research Institute (NGRI), Hyderabad; or CSIR-CIMFR, Nagpur.

The requirement is therefore not merely to submit a general geological report or a map downloaded from a public portal. The studies must meet the prescribed terms of reference and be conducted through a recognised institution.

How Annexure 24 affects new quarry applications

The stage at which the mandatory studies must be completed depends on the status of the quarry application.

Status of the proposed quarry	When the studies must be completed
Letter of Intent (LOI) granted, but Mining Plan not yet prepared	After LOI and before preparation of the Mining Plan
Mining Plan approved, but Environmental Clearance (EC) not obtained	Before grant of EC
LOI, Mining Plan approval and EC obtained, but quarry lease or permit not granted	Before grant of the lease or permit

These requirements are intended to bring the findings of the site-specific studies into the approval process before the relevant next-stage decision is made.

Annexure 24 also provides for consideration of qualifying studies already completed through the institutions specified in Section 7 after the date mentioned in the guidelines. Where only one of the two required studies has been completed, the other must also be undertaken. The reports and their recommendations must be considered before the relevant permission is granted.

For a new quarry proposal in an applicable High or Moderate zone, therefore, the macro-scale map is not the final technical assessment. The proposal must proceed through the prescribed site-specific studies and the relevant statutory approval process.

Meso scale study requirements as per Annexure 24

Section 14 of Annexure 24 of the Keralam State Disaster Management Plan, updated 2026, prescribes the requirements for slope-stability assessment for quarrying. The study must follow the GSI Standard Operating Procedure (SOP) for Meso-Scale (1:10,000/1:5,000) Landslide Susceptibility Mapping, 2021, subject to the modifications specified in the Annexure.

The assessment report must be prepared by one of the eight recognised institutions listed in Section 7. It must be submitted along with the mining application, included in the mining plan, or used to modify the existing mining plan, as applicable. The report must contain the following maps, assessments and recommendations:

Sl. No.	Requirement	Specification in Annexure 24
1	Institution conducting the study	The assessment report must be prepared by one of the eight recognised institutions listed in Section 7 of the guideline.
2	Methodology	Follow the Geological Survey of India (GSI) Standard Operating Procedure (SOP) for Meso-Scale (1:10,000/1:5,000) Landslide Susceptibility Mapping, 2021, with the modifications specified in the annexure.
3	Area to be mapped	The mining/quarry area and a 500 m buffer around it. The map is mandatory for all quarrying activities and must accompany the mining permit application.
4	Mapping scale	1:5,000.
5	Scale of thematic layers	All thematic layers used to prepare the landslide susceptibility map must also be at 1:5,000 scale.
6	Boulder assessment	In addition to the GSI SOP, assess boulders within the slope facet(s) encompassing the mining area. Identify and map all exposed and partly exposed boulders using appropriate methods.
7	Thematic maps	Include all thematic maps used to generate the landslide susceptibility map in the report.
8	Final susceptibility map	Include the final landslide susceptibility map with boulders clearly demarcated.
9	Field photographs	Include relevant field photographs wherever necessary.
10	Report and digital deliverables	Submit hard and soft copies of the report and thematic layers, and the final slope-stability assessment map in shapefile format.
11	Overburden management	Provide specific risk-management recommendations for overburden management.
12	Boulder management	Provide recommendations for managing boulders.
13	Rockfall and rockslide	Address possible rockfall/rockslide sites and recommend appropriate management measures.
14	Muck storage	Identify suitable sites for muck storage and recommend management measures to reduce slope-failure risk.
15	Hydrological management	Provide a surface and subsurface hydrological management plan to reduce slope-failure risk.
16	Material transportation	Recommend measures for material transportation to reduce slope-failure risk.
17	Other safety measures	Include other relevant recommendations considered necessary by the study team to ensure safe and secure quarrying operations.
18	Recommendations for local communities	Document the study recommendations in simple Malayalam and English so local communities can understand the findings and recommendations.

Download GSI's Standard Operating Procedure (SOP) for Meso scale (1:10,000/ 5000) landslide Susceptibility Mapping, 2021

What happens to existing operating quarries?

The guidelines also address quarries that already hold a valid quarrying permit or mining lease and are operating in areas covered by Annexure 24.

The District Geologist is required to identify the applicable existing quarries and direct the quarry applicant, owner or operator to complete the mandatory site-specific studies and submit the reports within six months from publication of the guidelines. The Annexure states that quarries that fail to submit the required reports within that six-month period must be stopped.

The Annexure also addresses studies already completed by recognised institutions after 16 March 2022. Such studies may be considered in the circumstances specified in the guidelines. If only one of the two studies has been carried out, the other must be completed, and the recommendations must be considered in deciding on continued operation.

This is a significant distinction between the treatment of new applications and existing quarries. A new proposal must complete the studies at the applicable approval stage. An existing quarry in the covered area is required to comply with the prescribed direction and deadline; the fact that it already has a permit or lease does not, by itself, exempt it from the studies.

Could existing quarry operations have influenced the mapped susceptibility category?

An important technical question arises from the data used for macro-scale landslide susceptibility mapping. The ASTER Global Digital Elevation Model (GDEM) Version 3 was generated using satellite scenes acquired between March 2000 and November 2013. The GSI Idukki study derived slope gradient, aspect and curvature from a 30-metre ASTER DEM and also incorporated land use/land cover as a susceptibility factor. Consider a quarry that has been operating for 10–15 years. During this period, excavation may have altered the original slope profile, curvature, vegetation cover and drainage pattern. If these changes are reflected in the elevation data or land-use imagery used for mapping, they may influence the calculated susceptibility value and, consequently, the mapped category. It is therefore possible that quarry-induced changes have contributed to an area being classified as having Moderate or High susceptibility, although this cannot be assumed without examining the source data and the actual map.

This possibility warrants technical examination, particularly where a regional susceptibility classification is being considered in relation to an existing quarry. However, the effect of quarry-induced changes on the mapped category cannot be established without examining the source data, mapping dates and relevant thematic layers. Any question concerning the applicability of Annexure 24 must also be decided in accordance with its actual provisions. A technical review of the mapping may help clarify the relationship between the regional classification and present site conditions, but it should not be taken as grounds for assuming that an existing quarry is safe or exempt from the prescribed studies.

How must the study recommendations be incorporated into the Mining Plan?

The studies are not intended to remain separate reports with no effect on quarry operations. Annexure 24 requires their recommendations to be incorporated into the Mining Plan or Modified Mining Plan, as applicable.

Where the Mining Plan has not yet been prepared, the relevant conditions from the study reports must be included when it is prepared. Where the Mining Plan has already been approved, the quarry applicant must prepare a Modified Mining Plan incorporating the prescribed recommendations and submit it for approval.

For projects requiring Environmental Clearance, the relevant mitigation measures must also be incorporated into the Mining Plan or Modified Mining Plan as part of the EC process. The State Level Expert Appraisal Committee (SEAC) and State Environment Impact Assessment Authority (SEIAA) are required to verify that the recommendations have been included as prescribed.

For existing quarries with valid leases or permits, the applicable mitigation measures must similarly be incorporated into a Modified Mining Plan and submitted to the competent authority. Annexure 24 assigns approval powers in this regard to the District Geologist, with the Director of Mining & Geology exercising the specified authority in cases where the matter falls within the Director’s jurisdiction, including relevant appeal matters.

The practical effect is that site-specific findings can influence the way a quarry is designed and operated. Recommendations may concern excavation geometry, slope management, drainage, boulder and overburden handling, storage of excavated material, blasting parameters and protective measures for nearby structures and slopes.

Does completing the studies automatically authorise quarrying?

No. Annexure 24 expressly makes the point that approval arising from the mandatory site-specific studies is not, by itself, the final permission to operate a quarry. All other applicable statutory approvals must still be obtained.

The studies provide technical evidence for the decision-making process. Their recommendations must be considered and incorporated into the relevant plans and approval conditions. The ultimate decision must take account of the findings, the proposed mitigation measures and the applicable legal requirements.

It is equally important not to assume that a study must necessarily result in approval. If the findings identify serious risks that cannot be adequately mitigated, those findings may affect whether and under what conditions the proposal can proceed. The decision should be based on the evidence and the applicable requirements, rather than on the regional map colour alone.

What this means in practical terms?

Consider two hypothetical quarry proposals.

The first lies in a High susceptibility zone. A detailed investigation may find competent rock, favourable geological conditions and manageable drainage, with the proposed excavation and blasting effects capable of being addressed through appropriate design and mitigation. The High classification signals the need for detailed scrutiny, but the site-specific findings are necessary to determine the actual constraints and measures required.

The second lies in a Low susceptibility zone. However, the proposed excavation may involve deeply weathered material, unfavourably oriented joints, groundwater seepage, removal of support at the toe of a slope and blasting near houses or roads. The Low classification does not establish that these local conditions are safe. If the quarry lies on a hill slope where a landslide has previously occurred, the applicability condition in Annexure 24 must also be examined.

These examples illustrate why the regional classification and the site-specific assessment must be read together. A colour on a regional map cannot substitute for investigation of the actual geology, slope conditions and effects of the proposed quarry operation.

Conclusion

The GSI’s macro-scale Landslide Susceptibility Zonation map is an important tool for preliminary identification of areas susceptible to landslides. Its High, Moderate and Low classifications provide a regional perspective, but they do not determine the safety of every individual quarry site.

Annexure 24 of the Kerala State Disaster Management Plan, updated 2026, builds on this distinction. For quarries in High or Moderate hazard zones, and for quarries on hill slopes where landslides have previously occurred, it prescribes site-specific Slope Stability and Blast Vibration studies, subject to the detailed applicability provisions. It also specifies the scale and coverage of the required susceptibility mapping, the institutions authorised to conduct the studies, the stages at which they must be completed, and the incorporation of their recommendations into Mining Plans or Modified Mining Plans.

For new quarry applications, these requirements affect the sequence of approvals. For existing quarries in the covered areas, they create a specific compliance obligation, including the six-month deadline for submitting the prescribed reports following publication of the guidelines.

The broader principle is straightforward: macro-scale mapping identifies where closer assessment is required; meso-scale mapping and site-specific studies provide the detailed evidence needed for decisions about quarrying. Neither the High classification alone nor the Low classification alone should replace a reasoned assessment of the actual site, the proposed activity and the measures needed to manage its risks.

The objective is not simply to approve or reject quarrying based on a map colour. It is to ensure that decisions are informed by the terrain, geology, slope stability, blasting effects and the potential consequences for people and infrastructure around the quarry.

 About the Author

Biju Sebastian is a retired Deputy Director of the Department of Mining and Geology, Government of Kerala. With over three decades of experience in mineral administration, mining laws, geology, GIS, and e-governance, he founded Mine Mapper, an independent platform dedicated to mining, geology, geospatial technologies, and digital solutions for the mining sector. Through Mine Mapper, he publishes the MiningWatch Kerala series featuring research-based articles, legal analyses, and technical insights on mining legislation, judicial decisions, environmental regulation, and mineral administration. The platform also provides practical digital tools and resources, including mine mapping applications, mining plan preparation tools, and other GIS-based utilities for professionals, industry, and the public.

Disclaimer

The views expressed in this article are those of the author in his personal capacity and are intended solely for educational and informational purposes. They do not represent the official views or policies of the Government of Kerala, the Department of Mining and Geology, or any other government authority.

This article does not constitute legal advice or an official interpretation of any law. Readers are advised to refer to the original Acts, Rules, Notifications, Government Orders, Circulars, and judicial decisions, or seek appropriate professional advice where necessary.

For the complete Disclaimer, please refer to the Disclaimer page.