Геология и природа Палау

none

The Republic of Palau consists of eight principal islands and more than 250 smaller ones lying roughly 500 miles southeast of the Philippines, in Oceania. The islands of Palau constitute the westernmost part of the Caroline Islands chain. The country includes the World War II battleground of Peleliu and world famous rock islands. The rock islands, the platform islands and the eastern half of Oreor Island are made up of Palau limestone. The limestone is raised coralline reef structure which formed in the warm tropical waters during Miocene to Pleistocene times. Surrounding the volcanic islands are natural terraced benches resulting from sea level changes and uplifting of the Palau ridge. Two levels of natural terraced benches have been recognized. One bench is 1 m to 2 m above mean sea level, while a second, and much broader, bench is 5 to 10 m above mean sea level. Many villages on Babeldaob Island are built on this second bench. Geologic data indicate that Babeldaob Island has undergone a net uplift of land relative to sea level of about 2 m in the last 4000 years; thus, for most of the Palau coastline, submerged habitation sites in intertidal and coastal swamp areas are unlikely. Excepting a few calcareous sand beaches, the rock island edges rise abruptly out of the water, forming steep cliffs. Distinctive geologic features of the rock islands are shear cliffs and a notch cut back into the cliff just above mean sea level.

The volcanic islands contain heavily eroded hills reaching heights of 250m above sea level, while the rock islands and atolls vary in elevation from sandy relict beaches a few meters above sea level to jagged limestone hills more than 200m high. The islands all are covered with dense stands of mixed tropical forest; in addition, the volcanic islands contain numerous areas of savanna and a broad belt of coastal mangrove swampland. An extensive barrier reef surrounds the central islands of the archipelago, forming a rich lagoon area of more than 1200 sq. km. Variations in soil type, elevation, and human activity have led to the development of distinctive plant communities. At present, only 75 % of the Palau Islands are forested, the rest being covered by secondary vegetation, marsh, grassland, crop land, urban development, or are barren. Several types of forest communities can be observed in Palau. Upland forests are found on the volcanic islands' uplands and include a great diversity of species. The variety of trees includes hard woods, palms, and pandanus. On the lower slopes, especially around settlements, the upland forest association becomes mixed with four other forest communities including the plantation forest, the palm forest, the agroforest, and the coconut plantation associations. These four forest communities include a wide variety of food producing species in tree gardens or kitchen gardens. Interspersed throughout these food producing forest associations are areas of cropland and urban development. The important resources of the food producing forest associations include coconut, breadfruit, mango, banana, almond, and betelnut. Important resources in the gardens include several species of targ cassava, pineapple, and tobacco Most cropland in Palau is divided into small garden areas. The swamp forest and mangrove forest associations are found on coastal lowlands where the terrain is level, especially surrounding the volcanic islands but also including large portions of Beliliou Island. These forests serve to hold eroding soil from washing into the lagoon and thus provide a natural buffer to protect the lagoon. The swamp forest is also found in upland areas on the volcanic islands where poor drainage conditions exist. Distinctive forest communities are found on the atolls, the rock islands and on the platform islands. Included in these communities is the casuarina forest with the needle bearing ironwood tree (ngas)." In addition to the forest associations on the volcanic islands are large areas of grasslands and savanna The grassland/savanna association accounts for 16% of the total area of Palau (6,783 hectares out of a total of 41,619) and most (99%) of this association is found on Babeldaob Island While some of this association is the result of human activity, at least a portion of the association is found on poor soils. In Palauan, these open areas are called ked. Most of the prehistoric terraces identified in Palau are associated with these unforested areas.

The relief of the country varies from the hilly main island of Babeldaob to the low, coral islands, usually bordered by large barrier reefs. Average altitude no data available; the lowest point is the water level of the Pacific Ocean (0 m); The highest point is Mount Ngerchelchuus (242 m).