C. Publications Presentation of papers on landslide research at local, regional and international conferences and seminars and publications.This is an effective mechanism to transfer the results of our work to interested agencies.
D. Research programmes. These include: study of landslide processes and neotectonics.
Since historic times multiple hazards related to hurricanes,
landslides, flooding and earthquakes have profoundly affected
the island of Jamaica. The high incidence of these geohazards
is due to a combination of geologic, geophysical, and
The island is located in the track of Atlantic hurricanes and within a seismically active plate boundary zone.
The citizens of Jamaica occupy a geologically active, young, heavily fractured, steep and rugged terrain where landslides are a principal process through which hill slopes evolve.
The bedrock is weak being deeply altered and weathered and is overlain by approximately 1.0m thick cover of residual soils. It comprises geologically young landforms and steep hillsides. As a consequence, the hazards that affect the island most frequently are landslides and flooding.
These hazards are important because of their frequency, associated loss of life, disruption of socio-economic activities and their effect on the built and natural environment.
Landslides and flooding account for most of the natural disasters that have occurred on the island during the last decade and continue to present common risks to life and property.
Landuse in Jamaica is changing rapidly in order to meet the economic and housing needs of the populace. It appears that the high incidence of landslide and flooding are symptomatic of this change.
The destructive potential of landslides, damage caused, and their role in the degradation of the watersheds is very well known to geoscientists, however, this information has not been effectively communicated to the citizenry.
In Jamaica, sediment supply as a consequence of landslides has reduced the
storage potential of water reservoirs. During the rainy
periods the water intakes for the Mona reservoir are
invariably choked with landslide debris.
Landslides frequently damage water supply pipeline.
Road cuts are prone to slope failures.
Slopes made bare by landslides are the sites of accelerated
soil erosion and appear to be a major cause of watershed
Landslide debris frequently chokes the rivers which results in
overbank flow and flooding.
Landslides recurrently affect agricultural lands, fruit trees
It follows from the above discussion that landslides are a force to reckon with and should be considered as a serious and recurrent natural hazard on the island.
Landslides and floods have caused death and injury , have damaged/ destroyed rural settlements, schools, public and private property, roads, bridges, culverts, retaining walls, agricultural lands and crops, water pipelines, electricity transmission lines and submarine cables. Accelerated soil erosion in the watersheds preferentially occurs on slopes made bare by landslides. The indirect economic costs are several orders of magnitude higher than the direct costs.
Natural disasters occur when individuals or whole communities
make plans based on insufficient consideration of the geologic
characteristics of the area. In some cases, the available
geologic expertise and knowledge has unfortunately not been
considered in the policy decisions on landuse. Why? It appears
that knowledge pertinent to societal welfare has not been
effectively delivered from experts to the public at large.
Losses and risks from recurrent natural hazards might be reduced and/or avoided if scientific data on physical environment in which we live are made available to all concerned.
SOCIETY NEEDS PRACTICAL AND TIMELY INFORMATION THAT MAY HELP IT TO EVALUATE IF HAZARDS THREATEN LIVES, ECONOMIC ACTIVITIES AND PROPERTY AND ALSO HOW TO PROACTIVELY RESPOND TO HAZARDOUS SITUATIONS.
The geologic processes that have created the beautiful landscape of Jamaica are the same which make it most vulnerable to geohazards.Therefore geoscience input must be a basis for prudent landuse.It is also of critical importance in environmental planning and management. Following quotation reflects the modern views on this approach. "Our society is just beginning to understand the potentially dangerous consequences of development and urbanization in geologically sensitive areas. Until recently, people were comfortable in assuming that engineering technology could overcome all environmental constraints and geological instabilities. Now the public, insurers, and policymakers share a growing concern for the episodic and catastrophic damage caused by the forces of nature" The Geological Society of America, 1997 The scientific literature on landslides and their management has witnessed a tremendous growth during the last two decades. However, in order to make disaster mitigation efforts more effective all those, especially non-geologists, who must use landslide information in landuse decisions must have some basic understanding of the subject. Also, as a matter of policy, all investigators must follow a standardized terminology to name, classify, map, describe and report landslides. These data along with a geologic background to landslides form the backbone for a simple and practical approach to landslide management through avoidance, control, removal and protection. A pre-requisite to hazard mitigation is that one must know what is it that one wishes to be mitigated. " In many ways- the main horror stories arise from the neglect of simple fundamentals- like look at the geology and geomorphology first- consider the influence of quaternary- don't unload slide toes- don't load their heads- all well known decades ago, but you know this very well " (Prof. John Hutchinson quoted in an article written by Prof. D. Brunsden, 1995). It is suggested that we describe a landslide following the terminology of Working Party On World Landslide Inventory (1990) " A landslide is the movement of a mass of rock, earth or debris down a slope". Some of the fundamental terms related to landslides are given in Boxes 1 and 2( Personal Communication DeGraff, 1998). Box No. 1 WHY LANDSLIDES? The geological processes and natural forces that have created the present-day landscape on the island of Jamaica are the same that makes it most vulnerable to natural hazards. Landslide activity is one of the principal geomorphic processes through which hillslopes evolve. These features represent locations where the resisting strength of rock and soil masses that make up a slope are overcome by the force of gravity which is constantly acting on a slope to move slope materials downslope. Every location on a hillslope can be considered as a part of a continuous tug-of-war between the driving force of gravity and resisting forces due to materials that constitute a slope. Both natural processes and human modifications of slopes can change this balance in the favour of gravity. The strength of the slope materials is reduced due to internal changes (weathering, seepage erosion, ground water changes etc.), while stresses on slope can be increased as a result of external factors (steepening of slopes through excavations, loading of slopes etc.). The landslide triggering mechanisms include : rainfall associated with tropical storms and/or earthquakes. BOX NO. 2 LANDSLIDE FUNDAMENTALS Types of landslide movement: 1. Landslides may occur as falls, topples, lateral spreads, slides, or flows. 2. Falls are masses dislodged from very steep slopes or escarpments which then free-fall, bounce, or roll downslope. Falls usually move very to extremely rapidly. 3. Topples are a forward rotation around a pivot point low or below one or more masses. 4. Lateral spreads are the result of movement involving lateral extension accommodated by shear or tensile fractures. This type of movement is earthquake-induced. 5. Slides displace masses along one or more discrete planes. Slides may either be rotational or translational in their movement. Rotational movement is where the plane is curved.The mass rotates backwards around a common point with an axis parallel to the slope. Translational movement is where the plane is more or less planar or gently undulating. The mass moves roughly parallel to the ground surface. 6. Flows are masses moving as a deforming, viscous unit without a discrete failure plane. 7. More than one form of movement may be represented in some landslides. Movement in this case is often described as complex. Landslide Materials: 1. Landslides may involve displacement of either ROCK, SOIL, or a COMBINATION of the two materials. 2. Rock refers to hard or firm bedrock, which was intact, and in place prior to slope movement. 3. Soil is used in the engineering sense to mean loose, unconsolidated particles or poorly cemented rock or inorganic aggregates. The soil may be residual or transported material. 4. Soil may be described as either DEBRIS or EARTH. Debris is engineering soil with 20 to 80 percent of the fragments larger than 2mm in size and the remainder smaller. Earth is when 80 percent or more of the soil consists of fragments 2mm or smaller LANDSLIDE TRIGGERING MECHANISMS IN JAMAICA: Slope movement processes observed in Jamaica are both a natural geodynamic phenomenon through which hillslopes evolve, as well as a consequence of changing land use following unsustainable development activities during the last 400 years. The most effective mechanism for triggering widespread landslide activity on the island is provided by the seasonal pattern of rainfall punctuated with intense storm events. In general, landslides follow sustained rainfall which recharges the soils and deeply weathered bedrock present on steep slopes. This condition favours the development of excessive pore-water pressures which tend to reduce the shear resistance in slope materials leading to widespread slope failures. For example, in one recorded instance, approximately 300mm of rainfall in 48 hours initiated shallow landslides that were quickly transformed into rapidly moving debris flows that caused extensive damage [Earle, 1991]. Earthquake events of Modified Mercalli Intensity VIII - X (greater than M 6.5) have been responsible for liquefaction and large scale landslides, whereas events below VIII have generally resulted in rock falls and debris slides [Ahmad, 1989c]. The earthquake of January 13, 1993 (M 5.4) triggered more than 40 landslides of different types in the parishes of Kingston and St. Andrew [Ahmad, 1993]. CASE STUDIES OF DAMAGE FROM LANDSLIDES The village of Preston in the Parish of St.Mary, Jamaica was an active farming community until May 1986. Slope movements in and around the village following May-June 1986 rainfall caused a widespread development of fissures, slumping and subsidence forcing residents to abandon their homes and farming lands. Today, Preston is a ghost village. The overall public reaction to this event was perhaps best summed up in an editorial in the leading newspaper of the country, the Daily Gleaner of 18th May 1986, which described it as "St.Mary Mystery" suggesting that there is no readily available explanation for this phenomenon. The causes of this misfortune for the citizens of Preston were landslides, which are a very common geologic hazard on the island. However, Preston is not the only place on the island that is affected by landslides. The Portland rainstorm of January 3-4, 1998, for example, triggered widespread landslides and related flooding in the Rio Grande Valley resulting in losses estimated by NRCA and ODPEM at hundreds of million dollars. In the Grants Level area, a landslide claimed the lives of four persons and left several others seriously injured. During the investigations on Preston landslide I had an opportunity to interview the 17 affected families and personally observed their suffering. Having lost their homes and farming lands, they had become "environmental refugees" because of a hazardous geologic process, which was amenable to correction and could possibly have been avoided or impact reduced. This event prompted me to research this subject in detail and it soon became evident that landslides in Jamaica are a force to reckon with and that scientific data to mitigate landslides are not adequate. LANDSLIDE IMPACT IN THE KINGSTON METROPOLITAN AREA: Landslides have occurred for thousand of years in KMA and rank high on the list of geohazards that affect this area. For the inhabitants of KMA, landslide hazard is a major constraint on land use. Unstable slopes pose a constant threat to their lives, property and the infrastructure, especially the road network. Landslides have affected both the natural slopes as well as those modified for human use and have caused significant damage to property and infrastructure. Some of the residential areas of Kingston and St.Andrew are located on marginally stable slopes that were disturbed by pre-historic and historic landslides. For example, the Geological Map of Kingston area prepared by the Geological Survey of Jamaica (1994 b) shows that between Papine and Jacks Hill landslips cover an area of some 0.8 km2 (80 hectares), or approximately 16.89 % of the total slope area of 4.75 km2. Many of these ancient landslide scarps and their deposits are concealed by vegetation and have been extensively modified by both natural processes and human interventions. These areas may remain stable for a long period of time until natural processes (e.g. intense rainfall) and/or human interference (e.g. construction activity) disturb the slope stability conditions. An excellent example of this is provided by the widespread occurrence of debris and mudflows in the Jacks Hill area that were triggered by the rainfall associated with 1973 tropical storm Gilda, and more recently, the rainfall during 20th October to 3rd November 1998. A number of retaining walls were also destroyed in this area as a consequence of the failure of backfill. The spectacular submarine landslide triggered by the MMI X, June 6, 1692, earthquake that destroyed the buccaneer town of Port Royal best illustrates the impact of landslides on the coastal environment of the capital city of Jamaica. This earthquake, as well as the M 6.5 Kingston earthquake of 1907, caused localized submarine slumping-related tsunamis and liquefaction in the coastal areas and also triggered widespread landslides in eastern Jamaica including the Port Royal Mountains. While not every landslide that has occurred in KMA since the time for which historic records are available can be classified as catastrophic, the cumulative damage from many small-scale rainfall induced landslides is more serious than a major slope failure. It has been estimated that during the period 1910 to 1965, for which published data are available, some 7. 3% of the total expenditure of the Public Works Department, Govt. of Jamaica, accounted for damage-repair costs related to landslides and flooding and this trend continues (Naughton, 1984). People are moving into hills because of the high rentals in the relatively flat areas of the Liguanea Plain. Traffic congestion has forced people to use hilly roads such as Jacks Hill Road and Skyline Drive. This has resulted in a significant increase in the number of motor cars on the landslide-prone roads. During the October-November 1998 rainfall, it was a common sight to observe road-users greatly inconvenienced by landslides, some were unable to make it to their workplace. In some cases, public and private passenger vehicles were observed to negotiate through active landslides while the road crews were removing landslide debris. Since the public is now more exposed to landslides, the potential for injuries and fatalities has also increased.Since 1991, death and injury as a result of landslides on the island seem to be a regular news feature. Hazards related to landslides are a major societal and environmental concern to Jamaica in general and the Kingston Metropolitan Area (KMA) in particular which is the main centre of the economic and industrial activity of the country. Recurrent landslide damage in KMA, caused specially by frequent rainstorms, should be a growing concern to the policymakers and planning agencies, Ministries of the government dealing with agriculture, transport, construction, housing and environment, health, security,Parish councils, Public utilities including water, electricity and telecommunications, farmers, tourism interests, and the general public. It has been estimated that throughout the Caribbean some US$15m is spent annually to repair the landslide damage to roads (DeGraff et al., 1989). Geological instabilities prevail over large sections of KMA. Many residential areas and infrastructure in KMA are located on large ancient landslides, and it is a common observation that new landslides have occurred on slopes that had previously failed. However, the real-world situation is that the small island states, such as Jamaica, have a limited land area which inspite of its natural constraints must be utilized to meet the needs of their peoples. The land area of Jamaica is some 11,000 km2, with about 80% of the slopes being above 200 , and a population density of 219 persons/km2. In KMA, which represents some 5% of the islands total area, the average population density is about 1264 persons / km2 and it hosts some 57% (approx. 700,000 persons) of Jamaica's total urban population. In this scenario the management of landslide hazard is especially important, and is also difficult and challenging. The answers lie in learning from the past examples of landslides that have occurred in KMA for thousand of years, in finding out why these landslides occurred and what was the direct and indirect damage they caused. Examples of some of these events have been presented with the aim of making planners, decision-makers, engineers, and public aware of the geological sensitivity of the terrain. Much of the landslide damage during the last 40 years appears to have occurred on slopes that have been modified for human use. The present-day landslide hazard is therefore symptomatic of changing landuse. " If human activities can cause or aggravate the destructive effects of landslides, they can also be used to eliminate or reduce them". LESSONS LEARNED Our studies have helped in identifying the controlling factors and mechanisms that favour the occurrence of landslides on the island. These are summarized below and may be successfully used to mitigate the hazard: A) Triggering mechanisms- Landslides are triggered both by earthquakes and heavy rainfall. All earthquakes with magnitudes 4.5 and over have caused landslides and 200-300mm rainfall in 48 hours initiates shallow landslides that are quickly transformed into debris flows that cause extensive damage. B) Landslides are strongly controlled by rock type and geologic structure with density of faults and joints being a very important factor. C) It has been demonstrated that most of the slopes are pre-disposed to landslides, which control the evolution of slopes on the island. This model should guide the watershed management strategies. The significance and impact of landslides has not been previously recognized. D) Damage from landslides is in most cases incorrectly ascribed to damage from floods. This must change if loss-reduction is to be achieved. In Jamaica, landslides frequently block the road network. This problem needs to be addressed promptly. Our results may help road engineers. In addition to controls by bedrock and structure, we have found that the landslide densities within 90m of roads are several orders of magnitude more than that beyond 90m from roads. Our results are supported by studies in Puerto Rico, which we have incorporated in our landslide modeling. PERCEPTION OF THE LANDSLIDE HAZARD: The general perception of the urban population living on a relatively flat area, however, is that following heavy rainfall landslides will occur on the mountainous roads and are regarded as erosion due to flooding. As far as we know, there is no insurance cover available for landslides. If a landslide blocks a road, it is the job of the Public Works Department to get the blockage cleared and depending upon the funds available carry out repairs. Since individual landslides are not spectacular events such as a hurricane or an earthquake and only directly affect a small section of the population at any locality, they are regarded as an inconvenience. Moreover, since the indirect effects and economic costs of landslides are not visible to a majority of population, landslides are not regarded as a serious hazard. The society, therefore, tends to follow the NIMBY approach when dealing with this hazard, which is- as long as it is not in my backyard, why bother. Public interest in landslides is aroused only in the cases of spectacular events that make news headlines because people are killed, injured or buried under the debris. This happens frequently in areas with a high population density. Although, in Jamaica, landslides are frequent, fatalities and injuries are low because of low population density in hills. However, this picture is changing rapidly. SAFETY FROM LANDSLIDES: The vulnerability of human life, property, and infrastructure to landsliding can be significantly reduced by avoiding slopes prone to landslides, restricting or prohibiting development in areas demarcated as flagged areas on hazard maps, and advising on appropriate engineering design. Local governments, community groups, and ODPEM can accomplish this by adopting landuse regulations and building codes. The existing structures, in particular lifeline structures, in landslide prone areas are amenable to standard physical mitigation methods. One of the strategies to reduce vulnerability to hazards is that the insurance industry uses the available information in enforcing premiums that reflect different levels of risk from hazards. It is important that strategies be formulated and implemented to (a) reduce losses from landslides, and (b) restrict development in more dangerous areas that are prone to landsliding. Proactive strategies of loss-reduction should be implemented in the planning stages of all new development projects. A SUCCESSFUL LANDSLIDE LOSS REDUCTION PROGRAMME IS POSSIBLE ONLY THROUGH THE ACTIVE PARTICIPATION AND COOPERATION OF BOTH THE CITIZENS AND THE ELECTED AND APPOINTED OFFICIALS OF THE GOVERNMENT. The very first step in loss-reduction is the availability of landslide susceptibility maps. LANDSLIDE HAZARD ASSESSMENT AND PREPARATION OF LANDSLIDE SUSCEPTIBILITY MAPS FOR KMA: The losses from landslides are termed vulnerability. This is one component in determining landslide risk. The other component is landslide hazard. Landslides are not currently amenable to risk assessment since there is no basis to determine the probability of landslides occurring within a given time period. Hazard assessments are possible and can be used in place of risk assessments. Hazard assessments are estimations of an area's susceptibility to landslides based on three inherent physical factors distribution of past landslides, slope steepness, and type of bedrock and its structure. We have mapped these three factors for KMA during 1996 to 1998. The degree of hazard is considered relative since it represents the expectation of future landslide occurrence based on the physical conditions of that particular area. Compilation of landslide hazard zonation maps is based on three principles (Varnes, 1984). First, the past and present are keys to the future; second, the main conditions that cause landsliding can be identified, and; third, degrees of hazard can be estimated. We employ the landslide susceptibility matrix technique (DeGraff and Romesburg, 1980) to identify areas with high susceptibility for future slope failure. This technique (often termed the "DeGraff method") relies on an inventory map of past landslides, and man-made factors that may contribute to landsliding. Basically, the various factor maps are overlaid to create a mosaic of small areas that contain distinct combinations of slope angle, aspect, geology, vegetation, landuse, etc. The landslide inventory map is then overlaid on this mosaic map, and those distinct combinations of factors that are associated with each landslide are tabulated and ranked. This ranking in turn is used to classify the entire study area into landslide susceptibility zones. Unfailed areas that share many common factors with failed areas are placed in the highest susceptibility class. In this project we use the IDRISI GIS software (Eastman, 1997) to construct a raster (cell-based) map of the KMA based on a 15m by 15m cell size. The study area contains 2,461,462 such cells. The GIS software to produce the final landslide hazard maps digitized the landslide inventory and factor maps. The landslide susceptibility in KMA has been presented on two derivative maps prepared on 1:50,000 metric topographic base maps, sheets 13 and 18, to portray deep-seated landslides in bedrock and shallow (active) landslides in the colluvium (that is, surficial materials on hill slopes). These maps are designated as: Landslide Susceptibility Classes- Deep Landslides, and Landslide Susceptibility Classes- Shallow Landslides. The purpose of these maps is to convey information on landslide susceptibility in KMA in non-technical form that may be understood by non-geologists. Only those geologic and geomorphic factors that have a direct bearing on the occurrence of landslides in the study area have been employed in the compilation of susceptibility maps. Since it is difficult, even in best possible conditions, to specify a time frame for the occurrence of landslides in any area, the landslide hazard is generally represented by landslide susceptibility. A landslide susceptibility map, such as the one presented, only identifies areas potentially affected and does not imply a time frame when a landslide might occur. In this report, and as is the general practice, landslide susceptibility will be referred to as landslide hazard. USES OF LANDSLIDE SUSECPTIBILITY MAPS: Preparation of landslide hazard zonation maps is a relatively young scientific pursuit. In some cases, the methodologies employed in map preparation are still in an experimental stage and many of the published hazard maps have not been field-tested. IT WAS POSSIBLE, HOWEVER, TO FIELD TEST THE HAZARD MAPS PRODUCED IN THIS STUDY. FOLLOWING THE HEAVY RAINFALL ASSOCIATED WITH HURRICANE MITCH AND RAINFALL ASSOCIATED WITH THE STATIONARY COLD FRONTS DURING 15TH OCTOBER AND 9TH NOVEMBER 1998 WIDESPREAD LANDSLIDES WERE TRIGGERED IN KMA. OVER 200 LANDSLIDE WERE MAPPED IN THE AREA AND A PRELIMINARY ANALYSIS OF THIS DATA VALIDATES THE ACCURACY OF THE KMA LANDSLIDE SUSCEPTIBILITY MAPS. Listed below are the main recommendations that will benefit a wide variety of users concerned with environmental management including disaster managers, planners and engineers. Landslide susceptibility maps can be used to: Recognize geographic areas where landsliding has already occurred and future landsliding is most likely, in other words , this map helps in understanding the constraints on land use and the scale of the landslide problems; Adopt appropriate strategies for dealing with the problems that may arise because of landslides on marginally stable slopes; Prepare for, modify, and/or mitigate the disastrous effects of landslides on communities and infrastructure by means of appropriate engineering practice and building codes; Regulating new development in hazardous areas through planning controls; and Public education. LANDSLIDE RISK can be computed using the susceptibility map together with information on existing or expected vulnerability. It is possible to estimate the risk associated with the critical facilities, especially the road network. Such information may be evaluated to arrive at a decision regarding an acceptable risk for a facility, or need for relocation, or applying appropriate mitigation measures. Planners may use different levels of landslide risk in KMA to control future development activities. The most practical and cost-effective loss reduction method is to avoid areas with a relatively high landslide hazard. If existing development falls under areas marked with a relatively high hazard and risk then preventive measures may be applied to counter the risk. Landslide hazard maps can be used for a qualitative assessment of accelerated soil erosion in the watersheds. Areas of high to moderately high landslide hazard in KMA surrogate for zones of accelerated soil erosion or vice-versa. Such areas may be left as forestlands. HOW TO USE HAZARD MAPS? Five levels of relative susceptibility have been identified on the KMA Landslide Susceptibility Maps: (1)low; (2) moderate; (3) moderate-high; (4) high; and (5) very high. Predicting absolute hazard is impractical with current capabilities. These zones do not imply legal restriction or regulation by zoning ordinances or laws as laid down by the local government authorities. Citizens, planners, engineers, and developers, however, can use these landslide hazard zonation maps as a tool to help reduce losses from existing and future landslides through prevention, mitigation, and / or avoidance. The map is intended primarily for the assessment of landslide hazard for planning purposes on a regional scale. Map indicates indirectly the extent and relative severity of landslide hazard and may be used in preliminary selection of areas for housing and infrastructural development. The enhanced readability of the map far outweighs the simplifications, errors and, omissions that could not be avoided. The map should not be used to determine the stability of specific building sites. The map can be used to identify areas where detailed geologic-geotechnical investigations are desirable prior to the development. Citizens may use the map in a general way to determine relative hazard, because chances of landslides occurring in areas in a high susceptibility zone (4) are greater than in areas under low zone (1). IT SHOULD BE UNDERSTOOD THAT NATURAL CHANGES AS WELL AS HUMAN-INDUCED CHANGES CAN AFFECT THE SUSCEPTIBILITY TO LANDSLIDES IN ANY AREA, AND THAT THE ABSENCE OF PAST OR PRESENT LANDSLIDES DOES NOT MEAN THAT SLOPE FAILURES WILL NOT OCCUR IN THE FUTURE. LIMITATIONS OF HAZRD MAPS: Like most regional landslide studies this study has limitations from several causes: deficiencies in the variable data set, non-correspondence between the available (surrogate) data and the actual physical mechanisms responsible for landsliding, and deficiencies in the DeGraff method of predicting landslide susceptibility. " The nation needs environmental leadership that can make positive advances, that can encompass all of its citizens, and be open to public scrutiny. We must strive to improve the process that develops our environmental policy. Our economy must be able to support the environmental costs, and provide for standard of living in addition to the environmental quality of life. We must develop policy that reflects a consensus of the people, and that encourages enthusiastic support and compliance. Setting standards, insisting upon high standards of ethics and truth, allowing for regional differences, and providing frameworks for evaluation of issues and results are crucial to long-term success. We have not yet reached these goals." By Lee C. Gerhard in " The dilemma of the geologist: Earth resources and environmental policy", Reviews in Engineering Geology, Vol. XII, p.7, 1998.
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