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
geographic factors.
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
degradation.
Landslide debris frequently chokes the rivers which results in
overbank flow and flooding.
Landslides recurrently affect agricultural lands, fruit trees
and crops.
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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