GIS in hazard mapping and vulnerability assessment on Montserrat.

INTRODUCTION

The British Government, the United Nations Development Programme (UNDP), and other international organizations have cooperated with the government of Montserrat in its massive efforts to rebuild socially and economically after its volcanic destruction in 1995.

In this connection, the Physical Planning Unit (PPU), in collaboration with the Department of Lands and Survey (L&S), has developed a GIS-based Land Information System (LIS) for effective planning and better management of land resources. LIS provides the basis for the development of a National Data Warehouse (NDW), which is effectively utilized for the better management of various public utility services and other resources of the country.

Moreover, GIS based LIS has proved to be an effective tool in disaster management. It is needed at all stages of disaster management, particularly mitigation, preparedness, response, and recovery. The demand for quick and accurate information and mapping where hazards exist can be met by the LIS. It allows for the analysis and visualization of a disaster situation, effectively reducing the loss of life and property.

This paper describes how GIS based LIS was implemented in hazard mapping and vulnerability assessment on Montserrat. It demonstrates the overall methodology adopted to achieve these objectives and gives an idea of the future potential of its application in the management of catastrophes.

Study Area

Montserrat, part of the Leeward Islands in the eastern Caribbean and overseas territory of the United Kingdom, is approximately 39.5 square miles in area. It lies approximately 27 miles southwest of Antigua (see Figure 1) and 1,150 miles north of the equator. This volcanic island is approximately 12 miles long and seven miles wide at its broadest point, with geographic coordinates of 16[degrees] 45' N, 62[degrees] 12' W.

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Montserrat has severely suffered in the recent past, particularly when a major volcanic eruption in June of 1997 completely destroyed nearly two-thirds of the island, including its airport, seaport, and the capital, Plymouth. Such devastation has had an unfavorable impact on its economic, social, environmental, and institutional infrastructures, resulting in an immediate migration of nearly 62 percent of its population to the United Kingdom, the United States, and other countries (see Figure 2).

The island has since been divided into two zones (see Figure 3): the safe area (1) and the unsafe area. (2) The safe area has been undergoing rapid development in terms of expanding road networks and the construction of buildings, all in an effort to provide facilities for the steadily re-increasing population. The unsafe area however, has been excluded from all development and human activities.

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VOLCANIC HAZARD ON MONTSERRAT

Based on the seventh meeting of the Scientific Advisory Committee (SAC) (3) on Montserrat Volcanic Activity that took place on August 28 to 30, 2006 (MVO 2006), it was concluded that the continued rapid growth of the lava dome posed a serious hazard to the nearby occupied communities. These hazards were pyroclastic flow from dome collapse and column collapse, rock avalanches from the collapse of the crater walls, and explosions with ash and rock fallout (see Figure 4).

The SAC advised that "the likelihood of these hazards is strongly controlled by the rate of extrusion, with high rates more likely to initiate both collapses and explosions." In this particular setting, a large dome almost reached the point where it was capable of overtopping the crater rim, and potentially being able to send pyroclastic flows in multiple directions. Figure 5 shows populated areas [1-3] at risk. The dashed line is the estimated southern boundary that can be reached by a pyroclastic surge produced by a collapse of 12 million cubic meters of dome material; the northern boundary of this is the solid line between Areas 1 and 2. The northern boundary of Area 2 indicates the limit, if 20 million cubic meters were to be produced by a collapse. The northern boundary of Area 3 marks the northern limit of any conceivable pyroclastic flows.

Thus, the role and importance of GIS was highlighted in this grave situation. It was important that the vulnerable population be highlighted if there were to be a collapse of 12 million cubic meters of material or more. The Disaster Management Coordination Agency found it beneficial to use GIS in ensuring mitigation measures were enforced.

Workflow

Using standard GIS techniques, the impressions prepared by the SAC, showing population Areas [1-3] in Figure 5, were transformed into GIS-ready "polygon shapefiles." After scanning and georeferencing the image, digitizing was carried out. These polygons then were overlaid on an aerial photograph of the area at risk (see Figure 6).

Based on the resulting images this map produced, it was decided that persons who fell within the 12M cubic meter and 20M cubic meter polygons be evacuated from their homes and relocated further north. This occurred successively in January and February of 2007. As a result of this evacuation, the safe area boundary line shifted further northward on two occasions, causing a decrease in the size of the area that was safe to occupy.

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Additional data was incorporated from the Land Information System (LIS), as shown in Figure 7. The names of owners were extracted to enable the Disaster Management Coordination Agency (DMCA) to personalize the emergency evacuation notice to those persons who were vulnerable and to ensure that these persons complied.

Police checkpoints were put in place on the ground to ensure that no unauthorized personnel entered the newly designated unsafe area. The GIS also was used to map these police checkpoints to ensure that all the routes in and out were covered by security (see Figure 8).

Analysis

Based on the advice of the Montserrat Volcano Observatory (MVO), (4) the DMCA requested that changes to the map be made as the situation at the volcano changes. It is useful to highlight the way in which the boundary of the safe and unsafe areas shifted during the course of the year 2007. As seen in Figure 9, the unsafe area increased in January 2007 (A), increased even further in February 2007 (B), but decreased significantly by September 2007 (C). This is a direct result of the ongoing activity at the Soufriere Hills Volcano.

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The MVO reported on January 3, 2007, that the dome was observed to have overtopped the crater wall. By January 4, 2007, there were simultaneous pyroclastic flows and ash venting, which reached an estimated 8,000 feet. Moreover on January 8, 2007, a pyroclastic flow entered Belham Valley (Area 1 in Figure 5), an area close to the occupied communities.

On February 7, 2007, a new lobe was discovered on the southwestern side of the dome, and there also was an increase in rockfall activity. On March 12, 2007, large pyroclastic flows went down the Tar River, which drains and dissects the Soufriere Hills in an eastern direction (a location in the designated unsafe area), and the spine that was growing on the northeastern side of the crater was lost.

Early in April of 2007, the dome growth terminated, and by May of 2007, the MVO noted that all measurable activity was low. After a period of low activity, the safe/unsafe boundary was restored in September of 2007.

The government of Montserrat, the DMCA, and the MVO now have adopted a Hazard Level System. The purpose of the system is to improve management of the ongoing eruption and to provide important information to the residents of Montserrat.

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The Hazard Level System divides the southern two-thirds of Montserrat into six zones with two Maritime Exclusion Zones (see Figure 10). Access permission for each of these zones depends on the hazard level.

The hazard levels, which range from 1 to 5 (see Figure 11), are set by the National Disaster Preparedness and Response Advisory Committee (NDPRAC) on the advice of the MVO.

CONCLUSIONS

The application of GIS in hazard mapping and vulnerability assessment on Montserrat has provided the disaster managers and the government of Montserrat with the necessary tools to manage a crisis on the island more efficiently. We have seen that hazard mapping is a quick way to inform residents of impending danger.

Moreover, GIS has proven a useful tool for the management of disasters and the relocation of residents during an emergency for it allows the potential for better decision making in an urgent situation. GIS techniques can be used to analyze and visualize an emergency situation, thus allowing decision makers to make informed decisions based on data they can see.

GIS further provides the means for different governmental agencies to participate in a full range of emergency management activities. Data is brought into one focus, helping to identify what needs immediate attention, what can wait, and what can be delegated. Having knowledge ahead of time can benefit those on the front line, such as the police, fire, and medical departments.

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Emergency crisis events impact more than just people and facilities. They also have an impact on the environment, crops, and livestock. This GIS tool has given the government of Montserrat impetus to continue to manage all limited resources (environmental, ecological, etc.) on the island in a sustainable fashion.

References

Government of Montserrat. 2009. Statistics Department, In Development Unit, D.O.F., Economic Development and Trade.

Montserrat Volcano Observatory. 2006. Http://www.mvo.ms. Seventh Technical Report of the Scientific Advisory Committee. 2006. Assessment of the hazards and risks associated with the Soufriere Hills Volcano, Montserrat.

(1) Safe area covers the north of the island, which is separated by an imaginary line recommended by the volcanic scientists. This area, as compared to the southern part of the island, is considered at minimal risk of volcanic activities.

(2) Unsafe area covers mainly the south and southeast areas of the island, which are in close proximity to the volcano, considered at high risk and thus excluded from all kinds of development and human activities.

(3) The SAC is responsible for assessing the hazards and risks associated with the Soufriere Hills Volcano, Montserrat.

(4) The MVO provides scientific advice to the civil authorities on the volcanic activity and the associated hazards and risks.

Lavern Ryan (Mrs.) obtained a Master of Science Degree in Geographical Information Science (Msc in GIS) in 2005 at the University of Edinburgh in Scotland. She is currently the GIS Manager, Physical Planning Unit, Ministry of Agriculture, Trade, Land, Housing, and the Environment, Brades, Montserrat, West Indies.

(Phone) ++6644916795

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