NATURAL HAZARDS PROFILE OF JAMAICA RAFI AHMAD rafi.ahmad@uwimona.edu.jm UNIT FOR DISASTER STUDIES DEPARTMENT OF GEOGRAPHY AND GEOLOGY Tel. 1-876-927-2728/2129 Fax: 1-876-977-6029 THE UNIVERSITY OF THE WEST INDIES AT MONA KINGSTON, JAMAICA http://www.mona.uwi.edu/uds/ Geology for Natural Hazard Loss-reduction and Environmental Management in the Caribbean CARIBBEAN REGIONAL DISASTER MANAGEMENT CONFERENCE November 1-3, 2004 Managing Hazards in a changing environment Wyndham Rose Hall Resort and Country Club Montego Bay, Jamaica
We consider natural hazards as natural earth processes/ natural events. Natural earth processes have endowed Jamaica with its beautiful landscape and resources including: Reefs, beaches, coastline, mountains, karst landscape-cockpit country, alluvial plains, groundwater, rocks, minerals, soils. Hill slopes evolve through landslides but this processes become hazardous when people live or work in areas where landslides occur or where land use changes, such as clearing a hill slope, may increase the incidence of landslides and/or flooding. NATURAL HAZARD (H) means the probability of occurrence within a specified period of time and within a given area of a potentially damaging phenomenon. For the purposes of this talk natural hazards in Jamaica are classified by their origin GEOLOGICAL HAZARDS : Earthquakes, liquefaction, tsunami; landslides, rock fall, debris flow, mudflow, submarine landslides; Subsidence; Volcanic activity and emissions (not applicable). HYDROMETROLOGICAL HAZARDS: Water floods, sediment water floods, debris flow, mudflow; tropical storms, hurricanes, storm surge, lightning, hail storms, drought, desertification. BIOLOGICAL HAZARDS: Outbreak of epidemic diseases, extensive infestations. (Not dealt here) MULTIPLE HAZARDS: Many natural hazards in Jamaica are caused by the same natural event. Since the inducing or triggering mechanism can interconnect several hazards this situation is described as multiple hazards or multi-hazards.
In Jamaica, as is the case in the rest of the Caribbean, the hazardous processes are multi-hazards, repititive, large-scale and difficult to control. NATURAL HAZARDS IN THE CARIBBEAN MAY BE REGARDED AS GEOLOGICAL, GEOPHYSICAL, AND GEOGRAPHICAL HANDICAPS. Hazardous effects and impacts are varied may be felt from a single household- an entire parish- entire island- entire region. We wish to point out that Hazard Assessment and Risk Assessment are not synonymous!
FREQUENCY AND IMPACT OF HAZARDS
Top 10 Natural Disasters in Jamaica sorted by numbers of people killed and affected Source: The OFDA/CRED International Disaster Database. Oct-30-2004. Disaster Wind Storm Flood Wind Storm Flood Drought Wind Storm Earthquake Flood Flood Wind Storm Date 12-Sep-1988 21-May-1991 11-Sep-2004 12-Jun-1979 1968 18-Nov-1912 14-Jan-1907 25-Apr-1979 15-May-1986 5-Aug-1980 Affected 810,000 551,340 350,000 210,000 100,000 94,820 90,000 40,000 40,000 30,009
Disaster Date Killed Earthquake 14-Jan-1907 1,200 Flood 6-Jan-1900 300 Wind Storm 17-Aug-1951 154 Wind Storm 18-Nov-1912 142 Flood 18-Nov-1940 125 Flood 23-Nov-1937 111 Wind Storm 10-Aug-1903 65 Wind Storm 22-Sep-1917 57 Flood 15-May-1986 54 Flood 4-Nov-1909 53
HIGH INCIDENCE OF HAZARDS IN JAMAICA IS DUE TO A COMBINATION OF SEVERAL GEOLOGICAL, GEOPHYSICAL, TECTONIC, AND GEOGRAPHIC FACTORS.
Plate tectonic setting
Storm surge, Harbour View: 10 September 2004
Natural hazards in the Caribbean From: Munich Re, 2002.
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Vertical Aerial Photograph of Liguanea Ridge
Irish Town Road Landslide 1988 ( Tyndale Biscoe Photo)
Landslides affecting roads, power lines, and domestic water supplies
Flood prone communities in Jamaica. Source: Water Resources Authority.
SPECTRUM OF HAZARD TYPES IN SMALL RIVER CHANNELS OF JAMAICA: sequence of competing events with decreasing gradient: debris slide or debris avalanche-debris flows- debris floods-floods. Population centres are located on debris fans developed along the interface of land and water- high liquefaction potential. Culverts and bridges located in debris flow segments must be designed to allow for the passage of rock debris and organic debris. Scale: Base of photo= Approx 1km. DEBRIS FLOW SEGMENT J.T. Biscoe Photo. DEBRIS FLOOD SEGMENT BLUEFIELDS 12 JUNE 1979 Caribbean Sea DEBRIS FAN
LANDSLIDES AND FLOODING IN HILLSIDE, ST. THOMAS, JAMAICA Rural community at Hillside was devastated by debris flows and debris floods in January 1993. Note the location of Hillside Primary School on a debris fan. Scale: Base of photo= Approx 1.2 km. LANDSLIDE AND DEBRIS FLOW SEGMENT Hillside Primary School Morant River Debris flood segment; Debris Fans. Hillside, St. Thomas, 27 January, 1993. Reproduced with permission of
DEBRIS FLOWS, June 1979 Flood rains, Bogue /Reading area
Debris flows, Blue Mountains, 12 September 1988.
Landslide and flooding processes in KMA:
Land degradation in Jamaica
Landslides are the principal cause of land degradation and land productivity in the tropics including Jamaica. Landslide susceptibility in Clarendon and St. Catherine draped on a DEM (Unit for Disaster Studies, UWI & British Geological Survey Project completed in 2002). Red areas indicate high landslide susceptibility and also are sites of accelerated soil erosion. Efforts to correct land degradation and loss of land productivity should take into consideration rainfall-induced landslides.
EARLY WARNING SYSTEMS
RAINFALL INTENSITY-DURATION THRESHOLD FOR SHALLOW LANDSLIDES IN EASTERN JAMAICA: Using data for 19 storms, 1951-2002, a threshold relation between rainfall intensity-duration and landsliding was established Threshold for rainfall-induced shallow landslides in Eastern Jamaica (1951-2002) 100 Rainfall Intensity (mm/hour) 10 1 1 10 100 1000 Rainfall Duration (hours) Rainfall events producing landslides (2001-2002) Storms that did not cause landslides (1993-1999) Rainfalls that caused landslides (1951-1988)
In Eastern Jamaica, rainfall threshold relation is defined for storms that had durations between 1-168 hours and average rainfall intensities between 2-93 mm/h. The threshold relations reported here are reasonable first approximations. The threshold relation indicates that for rainfall of short duration (about 1 h): Intensities > 36 mm/h, are required to trigger landslides. These storms trigger mostly shallow landslides by causing an excess pore pressure in shallow colluvial zones. Such landslides were typically associated with 2001-2004 type storms. Low average intensities of about 3mm/h appear to be sufficient to cause landslilding as storm duration approaches approximately 100 h. These triggered the largest, deepest landslides in eastern Jamaica, e.g., Flora, Gilbert, 2001 rainfall. Thresholds provide a key element of landslide warning system.
LANDSLIDE INTENSITY-DURATION RELATIONSHIP FOR HURRICANE GILBERT
Landslides are a gravity-induced natural erosional process through which hillslopes evolve and are triggered by both earthquakes and rainfall. They are distinct from simple gully erosion and sheet wash. The earthquakes of June 1692 and January 1907 and flood rains of June 1979 created hundreds of landslides which caused severe deforestation and erosion on the island. Threshold for earthquake-induced landslides in Jamaica.
Development in hazard prone areas
CONCLUSIONS
JAMAICA GEOSCAPE LANDSCAPE ELEMENTS AS NEOTECTONIC UNITS LIMESTONE PLATEAU WITH HILLS including the Cockpit country; 64% of the total land area; mainly in Cornwall and Middlesex, less in Surrey. Average annual rainfall 125-375 cm. MOUNTAIN RANGES covering 22% of the total land area; mainly in the Blue Mountains, Port Royal Mountains, and the hilly interiors in the parishes of St. Andrew, St. Mary, St. Catherine, Clarendon, St. James, Hanover, and Westmorland. Average annual rainfall 190-700 cm. COASTAL PLAINS, VALLEYS AND LAND- WATER INTERFACE covering 14% of the total land area; including areas under morass; plains of Liguanea, St. Catherine, Clarendon, Westmoreland, and Palisadoes tombolo. Average annual rainfall 190 cm. BEDROCK/ GEOTECHNICAL CHARACTERS Generally limestone, 52-11 m.y. old; uplifted in the last 23 m.y. Bedrock is extensively fractured with joints and faults common. Basement rocks, 124 to 53 m.y. old; include lava flows, pyroclastic rocks, granodiorite, volcanically derived sediments, limestone, igneous and metamorphic rocks. Bedrock is intensively jointed, faulted, altered and deeply weathered. Post 11 m.y., marine and non-marine rocks and sediments, time span; volcanics, marls, clays, clastics, limestone, raised reefs; poorly consolidated gravels, sands, silts & clays of alluvial fans; mostly developed along south coast LANDSCAPE AND ACTIVE PROCESSES Elev. 700-1000m, Max. elev. 2254 m, Blue Mts.; slopes > 25º; slopes > 30º; highly dissected; highly dissected; core of the island controlling karst ; water rainfall pattern; fault valleys accumulation Reproduced in and with fault permission scarps; surface of depressions; UDS. fault http://mona.uwi.edu/cardin drainage; landslides. scarps; landslides. Alluvial /debris fans; sand dunes; raised reefs; poljes. Active coastal processes; liquefaction and submarine landslides.
WATER RESOURCES Limestone aquifers, provide 96% of groundwater; 3294 Mm 3 yr -1. Springs. Basement aquicludes; provide 665 Mm 3 yr -1 of water as surface runoff. Springs. Alluvium aquifers; provide 4% of the groundwater; 124 Mm 3 yr -1 LANDSLIDE SUSCEPTIBILITY Moderate to high. Generally very high. Low; submarine landslides. TROPICAL STORM /FLOODING STORM SURGE Very high/ high Very high/ high. Very high/ high. High. EARTHQUAKE HAZARDS LIQUEFACTION TSUNAMI High. High. High. Subject to liquefaction. High. EROSION RATES Moderate to high. Very high. Low to moderate. LIMESTONE PLATEAU WITH HILLS MOUNTAIN RANGES COASTAL PLAINS, VALLEYS AND LAND- WATER INTERFACE
Natural hazards in the Caribbean From: Munich Re, 2002.
ACKNOWLEDGEMENTS Grateful thanks are extended to Miss Deborah-Ann Rowe and Mr. Leonard Notice.