Puerto Rico has 17 lakes, all man-made, and more than 50 rivers, most originating in the Cordillera Central. Rivers in the northern region of the island are typically longer and of higher water flow rates than those of the south, since the south receives less rain than the central and northern regions. Puerto Rico is composed of Cretaceous to Eocene volcanic and plutonic rocks, overlain by younger Oligocene and more recent carbonates and other sedimentary rocks. Most of the caverns and karst topography on the island occurs in the northern region in the carbonates. The oldest rocks are approximately 190 million years old (Jurassic) and are located at Sierra Bermeja in the southwest part of the island. They may represent part of the oceanic crust and are believed to come from the Pacific Ocean realm. Puerto Rico lies at the boundary between the Caribbean and North American plates and is being deformed by the tectonic stresses caused by their interaction. These stresses may cause earthquakes and tsunamis. These seismic events, along with landslides, represent some of the most dangerous geologic hazards in the island and in the northeastern Caribbean. The most recent major earthquake occurred on October 11, 1918, and had an estimated magnitude of 7.5 on the Richter scale. It originated off the coast of Aguadilla, several miles off the northern coast, and was accompanied by a tsunami. It caused extensive property damage and widespread losses, damaging infrastructure, especially bridges. It resulted in an estimated 116 deaths and $4 million in property damage. The failure of the government to move rapidly to provide for the general welfare contributed to political activism by opponents and eventually to the rise of the Puerto Rican Nationalist Party. The Puerto Rico Trench, the largest and deepest trench in the Atlantic, is located about 115 km (71 mi) north of Puerto Rico at the boundary between the Caribbean and North American plates. It is 280 km (170 mi) long. At its deepest point, named the Milwaukee Deep, it is almost 8,400 m (27,600 ft) deep, or about 5.2 miles.
Posted on: Sun, 17 Aug 2014 05:27:37 +0000
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