Unfortunately, human actions often increase the risk of landslides by modifying the landscape, building on unstable slopes or in the path of potential landslides.  It appears that many of us are completely unaware of our exposure to landslide risks. 

However, by understanding the answers to the following questions and learning from the past disasters and following the axiom “ present is key to the future”, we may be able to protect ourselves from the effects of landslides.

WHY SHOULD WE BE CONCERNED ABOUT LANDSLIDES?

In Jamaica, the wider Caribbean, and also worldwide landslide disasters cost more money each year than all other natural disasters combined, and their incidence appears to be rising. Yet they get little public attention.

View of Jamaican professionals on landslide costs to nation:

On January 26-28, 1999 Unit for Disasters Studies hosted a workshop on issues of landslide hazard mitigation and loss-reduction strategies. Some 40 Jamaican professionals representing fields of geology, engineering, water and transportation, disaster response, development and urban planning, and environmental management were in attendance.

 We decided to take advantage of this occasion in order to document how well landslide information was understood by an array of staff support personnel for decision makers. The questions and responses that follow are anecdotal in nature and limited in number. A more comprehensive survey is surely warranted, but we believe that what is captured here reflects the general attitude about this subject that prevails, not only in Jamaica but seemingly everywhere else in the world.

 Q. WHAT IS THE YEARLY-AVERAGE COST OF LANDSLIDE DAMAGE FOR JAMAICA AND/OR FOR YOUR JURISDICTION? All responses are in Jamaican dollars.

A. $5 billion   $3 billion   $180 million   $80 million

The range in answers covers about two orders of magnitude. Estimating costs of landslide damage is always problematic as the direct and indirect costs are rarely collected by a central agency.  From the above range it is understandable why the disparity of opinions exist regarding the severity of the landslide-hazard issue.

 Q. ARE THE EFFECTS OF LANDSLIDE DAMAGE INCREASING, AND IF SO WHY?

A. All Jamaicans answered YES. The reason for the YES responses include:

• Increased development in marginal areas
• Human encroachment in vulnerable areas
• Squatting
• Deforestation
• El Niņo
• Road construction

The population in Jamaica is reasonably stable. However, the segment of the population that is gaining wealth is moving into hillside settings. Thus, the number of new mountain roads and terraced slopes is increasing, and it is easy to understand why there is a perception that landslide damage would be increasing.

HOW CAN WE MINIMIZE THE EFFECTS OF LANDSLIDES?

 Landslide Hazard: as represented by susceptibility, which is the likelihood of a potentially damaging landslide occurring within a given area.

Vulnerability: the level of population, property, economic activity, including public services, etc., at risk in a given area resulting from the occurrence of a landslide of a given type.

Risk (specific): the expected degree of loss due to a particular landslide phenomenon.

 LANDSLIDE RISK MANAGEMENT:

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 a few key factors. These are each capable of being mapped and allow land areas to be evaluated on their relative susceptibility to landslides.

 Three principles guide landslide hazard assessment. First, landslides in the future will most likely occur under geomorphic, geologic, and topographic conditions that have produced past and present landslides. Second, the underlying conditions and processes which cause landslides are understood. Third, the relative importance of conditions and processes contributing to landslide occurrence can be determined and each assigned some measure reflecting its contribution . The number of conditions present in an area can then be factored together to represent the degree of potential hazard present. THE AIM IS TO PRODUCE A LANDSLIDE HAZARD MAP THAT IDENTIFIES AREAS WHERE FUTURE LANDSLIDING IS MOST LIKELY TO OCCUR. THIS MAP FOREWARNS PLANNERS AND ENGINEERS OF SLOPE INSTABILITY CONSTRAINTS ON THE MOUNTAINOUS TERRAIN .

GIS-based Landslide susceptibility maps for the Kingston Metropolitan Area, guidelines on their use, and loss-reduction strategies are available at <http://isis.uwimona.edu.jm/uds/index.html >. Other areas in Jamaica where landslide hazard mapping has been completed and maps available in public domain include Clarendon and St.Catherine, South Coast of Jamaica, and RioGrande Valley, Portland.

Shallow Landslide Susceptibility Map click for large-size map or for legend or for guidelines

Deep Landslide Susceptibility Map click for large-size map or for legend or for guidelines

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. Agencies including ODPEM, NEPA, Town Planning Department, Parish Councils, and Community Groups can accomplish this by adopting land use 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.  Proactive strategies of loss-reduction should be implemented in the planning stages of all new development projects.

The lessons learned from the previous disasters should be used to adopt prudent  land use policies, institute proper design,

strengthen weak structures, and design preparedness plans at national, community, and family  levels. This information

should assist general public, planners and decision makers to take appropriate actions that may help to reduce losses from the

future natural hazards

RESPONSE TO DEBRIS FLOWS, REPRODUCED AND MODIFIED FROM U.S.GEOLOGICAL SURVEY FACT SHEETS:

The following response to debris flow hazards is from the guidelines provided by the United States Geological Survey in the Landslide Hazard Fact Sheets, 1999-2000. These guidelines are very useful for Jamaica as we are in the hurricane season. 

What are debris flows?

Some landslides move slowly and cause damage gradually, whereas others move so rapidly that they can destroy property and take lives suddenly and unexpectedly. Debris flows (also referred to as mudslides, mudflows, or debris avalanches) are a common type of fast-moving landslide that generally occurs during intense rainfall on water-saturated soil. They usually start on steep hillsides as soil slumps or slides that liquefy and accelerate to speeds as great as 35 miles per hour (56 km/hour) or more.  They continue flowing down hills and into channels and deposit sand, mud, boulders, and organic material onto more gently sloping ground. Their consistency ranges from watery mud to thick, rocky mud (like wet cement), which is dense enough to carry boulders, trees, and cars. Debris flows from many different sources can combine in channels, where their destructive power may be greatly increased.

HOW TO IDENTIFY HAZARDOUS AREAS?

Debris flows start on steep slopes-slopes steep enough to make walking difficult. Once started, however, debris flows can travel even over gently sloping ground. The most hazardous areas are valley bottoms, stream channels, areas near the outlets of valleys and gorges, and slopes excavated for buildings and roads.

It may be possible for individuals to easily  identify the features shown in the following illustration.

A: Valley bottoms, stream channels, and areas near the outlets of valleys or channels are particularly hazardous. Multiple debris flows that start high in stream courses commonly funnel into channels. There, they merge, gain volume, and travel long distances from their sources.

B: Debris flows commonly begin in swales (depressions) on steep slopes, making areas down slope from swales particularly hazardous.

C: Road cuts and other altered or excavated areas of slopes are particularly susceptible to debris flows. Debris flows and other landslides onto roadways are common during rainstorms, and often occur during milder rainfall conditions than those needed for debris flows on natural slopes.

D: Areas where surface runoff is channeled, such as along roadways and below culverts, are common sites of debris flows and other landslides.

What can you do if you live near steep hills?

These tips may save your life and property.

Prior to approaching hurricanes and other storms:

1. Become familiar with the land around you. Learn whether debris flows have occurred in your area by contacting UDS at UWI, ODPEM, NRCA, UWA, MGD, or your Parish Disaster Coordinator. Slopes where debris flows have occurred in the past are likely to experience them in the future.

 2. Support Town Planning Department and Parish Councils in their efforts to develop and enforce land-use and building ordinances that regulate construction in areas susceptible to landslides and debris flows. Buildings should be located away from steep slopes, streams and rivers, intermittent-stream channels, and the mouths of mountain channels.

 3. Watch the patterns of storm-water drainage on slopes near your home, and note especially the places where runoff water converges, increasing flow over soil-covered slopes. Watch the hillsides around your home for any signs of land movement, such as small landslides or debris flows or progressively tilting trees.

 4. Contact your parish council to learn about the emergency-response and evacuation plans for your area and develop your own emergency plans for your family and business.

 During Intense Storms:

1. Stay alert and stay awake! Many debris-flow fatalities occur when people are sleeping. Listen to a radio for warnings of intense rainfall. Be aware that intense short bursts of rain may be particularly dangerous, especially after longer periods of heavy rainfall and damp weather.

 2. If you are in areas susceptible to landslides and debris flows, consider leaving if it is safe to do so. Remember that driving during an intense storm can itself be hazardous.

 3. Listen for any unusual sounds that might indicate moving debris, such as trees cracking or boulders knocking together. A trickle of flowing or falling mud or debris may precede larger flows. If you are near a stream or channel, be alert for any sudden increase or decrease in water flow and for a change from clear to muddy water. Such changes may indicate landslide activity upstream, so be prepared to move quickly. Don't delay! Save yourself, not your belongings.