Puerto Rico, a territory of the United States has an area of 3,515 square miles, about 70 to 80 percent of which is hilly or mountainous. Approximately 60 percent of the population of 3.5 million lives in the four largest cities, San Juan, Ponce, Mayaguez, and Arecibo. Those cities are located on flat or gently sloping coastal areas. The rapid urbanization in these cities has pushed development onto surrounding steep slopes. The mountainous Cordillera Central, which forms the spine of Puerto Rico, has a cool environment due to it’s elevation (4,390 feet above sea level at it’s highest point) and receives considerable rainfall year round. This area includes the only tropical national rainforest in the United States, El Yunque, (“whose name may be attributed to either a Spanish approximation of the “aboriginal Taíno word yu-ke which means "white lands", or the word "anvil," which is yunque in Spanish”).
A warming atmosphere causes more evaporation, meaning more water is available for precipitation. For every 1°F increase in temperature, the atmosphere can hold around 4 percent more water vapor, which leads to heavier rain and increases the risk of flooding of rivers and streams. We saw the impact of extreme rainfall during Harvey. Though no research has yet been done to attribute the staggering rainfall totals from this storm to climate change, the downpours are very much in line with heavy precipitation trends.The University of the Caribbean identifies the types of landslides that occur on the island of Puerto Rico.
All major types of landslides occur in Puerto Rico, and all physiographic provinces of the island have landslides. Most of the Upland province and the Northern Karst province (Fig. 17), by virtue of high relief, steep slopes, and abundant rainfall, have continuing landslide problems. The drier southwestern part of Puerto Rico (Fig. 16) normally experiences landslides only during exceptionally heavy rainfalls; few landslides form there during periods of normal precipitation. The coastal plain has only localized landslide problems, predominantly along incised stream channels or where steeper inselbergs project through the younger surficial sediments.
Debris slides and debris flows—rapid downslope sliding or flowing of disrupted surficial rock and soil—are the most prevalent types of landslides in Puerto Rico. These landslides are particularly hazardous because they form with little or no warning and can move very rapidly down steep slopes. Structures at the base of such slopes are inundated or destroyed by the impact of the rapidly moving mixture of soil, rock, and water.
A common, but less abundant, type of landslide is rock fall—rapid movement by free fall, bounding, or rolling of bedrock detached from steep slopes. Rock falls are common on very steep natural slopes and especially on the numerous steep road cuts on the island. These landslides can be very damaging if they impact structures or passing automobiles. Recent major storms have triggered many rock falls of different sizes that closed roads and temporarily isolated parts of the island.
Block slides and slumps—masses of bedrock and overlying soil that move downslope either as intact blocks or as a collection of slightly disrupted blocks—are less common than debris slides and debris flows, but their effects can be catastrophic. Such was the case during the October 1985 storm, when the Mameyes district of Ponce was destroyed by a block slide that killed at least 129 people (Jibson, 1986a, in press). Block slides and slumps can disrupt large areas of the ground surface and thus lead to destruction of overlying structures and burial of structures downslope.
Earth flows—normally slow-moving masses of moderately disrupted earth that can move down even very gentle slopes—also occur in Puerto Rico. This movement commonly causes sufficient deformation of the ground surface to damage or destroy overlying structures or roads.
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