|
Taiwan 2002 |
 |
 |
Geography |
||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
TaiwanOff the eastern coast of Asia lie the mountainous island arcs of the Western Pacific. The island chain closest to the continent marks the edge of the Asiatic Continental Shelf. Taiwan, one of the islands of this chain, is the largest body of land between Japan and the Philippines.The island of Taiwan is 394 km long and 144 km at its widest point, shaped like a tobacco leaf. It is located between 21 deg 3'50" and 25 deg 8'20" N latitude and between 120 deg 1'00" and 121 deg 9'15" E longitude.
With a total area of nearly 36,000 sq. km, Taiwan is separated from the Chinese mainland by the Taiwan Strait, which is about 220 km at its widest point and 130 km at its narrowest. The island is almost equidistant from Shanghai and Hong Kong. The surface geology of the island varies in age from very recent alluvial deposits to early sedimentary and crystalline rocks. The structure is formed by a tilted fault block running roughly northeast to southwest along the entire length. The steep slope of this tilted block faces east and the rock mass slopes more gently to the west. This block is composed primarily of old rocks, some of which have been subjected to heat and pressure. Only one-third of the land area is arable. The mountains are mostly forested, with some minerals, chiefly coal, at the northern end.
On the east coast, the mountains rise steeply from the Pacific. To the west, the level sediments lie just below the surface of the sea. As a result, river deposits have filled the shallow waters and extended the land 15 to 30 km westward from the foothills, giving Taiwan a larger proportion of useful level land than either Japan or the Philippines. Natural resources and agricultural potential make this coastal plain of great importance.
The shoreline of Taiwan is relatively smooth and unbroken with a total length of 1,566 km (including the Penghu Islands). Off the southern end of the island lie small area of coral reefs, which have built up along the island's shores. The most important feature of Taiwan's topography is the central range of high mountains running from the northeast corner to the southern tip of the island. Steep mountains over 1,000 meters high constitute about 31 percent of the island's land area; hills and terraces between 100 and 1,000 meters above sea level make up 38 percent; and alluvial plains below 100 meters in elevation, where most communities, farming activities, and industries are concentrated, account for the remaining 31 percent. Based on differences in elevation, relative relief character of rock formations, and structural patterns, the island can be divided physiographically into five major divisions: the mountain ranges, volcanic mountains, foothills, tablelands, and coastal plains and basins.
Mountain RangesTaiwan's five longitudinal mountain ranges occupy almost half of the island. As a group, they extend 330 km from north to south and average about 80 km from east to west. They include more than two hundred peaks with elevations of over 3,000 meters.Central RangeThe Central Range 中央山脈 extends from Suao 蘇澳 in the north to Oluanpi 鵝鑾鼻 in the south, forming a ridge of high mountains and serving as the island's major watershed for rivers and streams. The range is predominantly composed of hard rock formations resistant to weathering and erosion, although heavy rainfall has deeply scarred the sides with gorges and sharp valleys. The relative relief of the terrain is usually extensive, and the forest-clad mountains with their extreme ruggedness are almost impenetrable. The east side of the Central Range is the steepest mountain slope in Taiwan, with fault scarps ranging in height from 120 to 1,200 meters.
Mount Snow RangeThe Mount Snow Range 雪山山脈 lies northwest of the Central Range, beginning at Santiao Chiao 三貂角 in the northeast and gaining elevation as it extends toward the southwest. Mount Snow 雪山, the main peak, is 3,884 meters high.Mount Jade RangeThe Mount Jade Range 玉山山脈 runs along the southwestern flank of the Central Range. It includes the island's tallest peak, the 3,952-meter Mount Jade 玉山.Mount Ali RangeThe Mount Ali Range 阿里山山脈 lies west of the Mount Jade Range, with major elevations between 1,000 and 2,000 meters. The main peak, Mount Ta 塔山, towers 2,484 meters.East Coastal RangeThe East Coastal Range 東部海岸山脈 extends from the mouth of the Hualien River 花蓮溪 in the north to Taitung County 臺東縣 in the south, and chiefly consists of sandstone and shale. Although Mount Hsinkang 新港山, the highest peak, reaches an elevation of 1,682 meters, most of the range is composed of large hills. Small streams have developed on the flanks, but only one large river cuts across the range. Badlands are located at the western foot of the range, where the ground water level is the lowest and rock formations the least resistant to weathering. Raised coral reefs along the east coast and the frequent occurrences of earthquakes in the rift valley indicate that the fault block is still rising.Volcanic MountainsAlthough igneous rocks are not commonly found in Taiwan, smaller outcroppings of extrusive bodies are scattered over the island, representing at least five periods of igneous activity.The Tatun mountain area 大屯山 is a prominent group of volcanic peaks, lying at the promontory between Keelung Port 基隆港 and the Tamsui River 淡水河 overlooking the Taipei metropolitan area. The entire area is covered by lava that poured out of the volcanic craters which now stand as conical notches of over 1,000 meters. The area is unique for its hot springs and fumaroles. FoothillsThe foothills are found in a narrow zone surrounding the Central Range. This zone, with an elevation of from 100 to 500 meters, is connected with the Central Range and linked with the tablelands in continuous slopes. Low hills with gentle slopes and longitudinal valleys woven with transverse gullies are characteristic topographic features of this zone, as are broad escarpments and short hogbacks formed on fault scarps or along rock formations.Along the Central Range, the Keelung-Miaoli foothills and those extending from Chiayi 嘉義 to Pingtung 屏東 are the broadest. The Keelung-Miaoli foothills start from the coast at Keelung 基隆 and end at south of Miaoli 苗栗. The Chiayi foothills rise below Mount Ali, with their northern border on the Choshui River 濁水溪 and the southern border between Kaohsiung 高雄 and Pingtung. There is a shallow-faulted region between these foothills and the Fengyuan foothills, extending from Fengyuan 豐原, just north of Taichung 臺中, to Nantou 南投, some distance to the south. This is the widest section of western foothills in Taiwan. It is intersected by three rivers: the Tachia 大甲溪, Tatu 大肚溪, and Choshui. Included in this region is the Sun Moon Lake Basin 日月潭盆地, which lies about 765 meters above sea level and forms a graben basin. At the southern flank of the Central Range are the Hengchun foothills that occupy most of the Hengchun Peninsula 恆春半島. The topography is down-graded on the eastern and western sides. Terrace TablelandsFrom the foothills, the terrain is gradually reduced to tableland from 100 to 500 meters in height. These thick deposits of well-rounded sandstone gravel are accumulations of eroded material washed down from higher areas. The gravel beds may have been deposited near the sea and then raised into flat-topped tablelands by recent tilting. The broadest tableland is the one between Taoyuan 桃園 and Hsinchu 新竹 in northern Taiwan. Next in size are the Houli Terrace 后里臺地 in Taichung, the Tatu Terrace 大度臺地 and the Pakua Terrace 八卦臺地 in Changhua 彰化, and the Hengchun Terrace 恆春臺地 in southern Taiwan. Coastal Plains, Basins, and Valleys
To the west, the physical character of Taiwan changes through the foothills zone to the alluvial plain. Topographically, the coastal plains and basins are monotonously flat, except near the foothills. All of the larger rivers running through the plains have their sources in the high mountains. Flowing out of the western foothills, these rivers diverge into a number of channels and meander to the ocean, forming large alluvial deltas. Many of these have been linked by irrigation and drainage canals. The coastal plains are generally covered with gravel, sand, and clay, with an average slope of between 0.5 meters and one km. Slopes are gentle enough to eliminate the need for major terracing and are rarely subject to serious soil erosion. The western edge of the plain, where it meets the Taiwan Strait, is marked by wide tidal flats and the coast is swampy. Shore currents have built up a series of spits and offshore bars, with many lagoons formed by shoreward shifting of the sandbars. The Chianan Plain 嘉南平原 is the broadest in southwestern Taiwan, extending from Changhua to Kaohsiung. It is about 180 km long and 43 km wide at its broadest point, making up more than 12 percent of the total land area of Taiwan. Next largest are the Pingtung Plain 屏東平原 and the Ilan Plain 宜蘭平原. Finally, there are two major basins, the Taipei Basin 臺北盆地 and the Taichung Basin 臺中盆地. The East Longitudinal Valley 臺東縱谷 is an extremely narrow fault valley in proportion to its length. It has a general elevation of about 120 meters above sea level and dips slightly toward the east. Coalescing alluvial fans have developed at the foot of both sides, and the river beds are filled with gravel. Due to repeated movements along the fault line and frequent shocks, subordinate watersheds have developed in the valley. RiversThe Central Mountain Range is the major watershed for Taiwan's rivers and streams; thus, most rivers in Taiwan flow in either an easterly or westerly direction. They are short and steep, especially on the eastern side of the island, and become torrential during heavy rainstorms, carrying heavy loads of mud and silt. The riverbeds tend to be wide and shallow, making them difficult to manage and develop as water resources. Taiwan has 151 rivers and streams. The Choshui River is the longest (186 km), while the Kaoping River 高屏溪 has the largest drainage basin (3,257 sq. km).
Natural Vegetation and SoilsBecause of Taiwan's location, plant species are diverse and abundant. The high altitude of the island's mountains provides climatic and vegetation zones ranging from subtropical to alpine. Except for the western coastal plain and the Penghu Islands, Taiwan was once entirely covered by forests. The forested area today is estimated at 1.9 million hectares.Acacia trees are ubiquitous on lower hills. Bamboo groves and forests are found naturally in central and northern Taiwan, whereas in the south, most stands of bamboo are cultivated on farms. Outside of forests, bamboo is normally confined to relatively moist areas; thus, it can be cultivated almost anywhere in the Taiwan area. The flora of Taiwan resembles that of the Chinese mainland. A wide range of Asian subtropical species are found in the lowlands, and low altitude flora is closely related to that of the southern Chinese provinces. Mountain flora is related to that of western China, and high alpine flora to that of the Himalayan region. Soils vary in fertility. Many have lost their natural fertility after centuries of irrigation and heavy rainfall. In the north, the soils of arable land are primarily acid alluvials and latosols of diluvial, some of which are residuals. In the southwest, where agricultural production is concentrated, most of the arable soils are alluvials of neutral to weak alkalinity and planosol-like alluvials. Upland soils of mountainous areas are mostly lithosols, which are usually thin and infertile. ClimateSituated off the east coast of Asia and in the path of warm ocean currents, Taiwan has an oceanic and subtropical monsoon climate, conspicuously influenced by its topography. Summers are long and accompanied by high humidity, while winters are short and usually mild. In the coldest months, snow is visible on the peaks of high mountains. Frost is rare in the lowlands, where most of the population lives and works. The mean monthly temperature in the lowlands is about 16 deg C in the winter, and ranges between 24 deg C and 30 deg C the rest of the year. The relative humidity averages about 80 percent.Taiwan is in the trade wind belt of the planetary wind system and is greatly affected by the seasonal exchange of air masses between the continent and the ocean. Besides location and topography, the winter (northeast) and summer (southwest) monsoons are the main factors controlling the climate of Taiwan.
The different directions of the winter and summer monsoons cause seasonal distribution of rainfall in northern Taiwan to be different from that in the south. The northeast monsoon 東北季風 in the winter lasts about six months from October to late March and brings steady rain to the windward (northeast) side of the island. The central and southern parts of the island, however, are on the leeward side of the northeast monsoon; thus, they have sunny winters, with less than 30 percent of their annual precipitation falling at this time. The annual "Plum rain" season in May and June brings a lot of precipitation. In the summer, the southwest monsoon 西南季風 prevails for about five months, beginning in early May and ending in late September. During this period, southern Taiwan usually has wet weather, while northern Taiwan is relatively dry. The moisture, carried by the southwest monsoon and local terrestrial winds, falls largely in convectional form. Thundershowers and typhoons bring Taiwan heavy rainfall during the summer months. Taiwan lies in the path of severe tropical cyclones known in East Asia as typhoons. With their violent winds and extremely heavy rainfall, these storms often cause severe damage, especially to crops. However, they are the greatest source of water in the Taiwan area. During a typhoon, windward mountain slopes may receive as much as 300 mm of rainfall in 24 hours. An average of three to four typhoons hit Taiwan every year, usually in July, August, or September. However, in 2000 seven typhoons, Kaitak, Bilis, Prapiroon, Bopha, Yagi, Xangsane, and Bebinca hit the Taiwan area (see chart). Kaitak, Bilis, and Xangsane brought torrential rains. Xangsane alone caused 64 deaths. And the agricultural losses of Bilis and Xangsane were estimated at US$152 million and US$115 million respectively.
According to a statistical analysis by the Water Resources Bureau (WRB) of the Ministry of Economic Affairs 經濟部水資源局 based on data collected from 1949 to 1990 at 440 rainfall gauging stations, the mean annual rainfall in the Taiwan area is 2,515 mm, with the hills receiving more than 5,600 mm, and lowland areas at least 1,200 mm. Rainfall is most abundant in the north with mean annual rainfall at 2,934 mm, followed by the eastern region at 2,715 mm, the southern region at 2,501 mm, and the central region at 2,081 mm. The southern area of Taiwan receives 90 percent of its rainfall between May and October. In the north, the seasonal distribution of precipitation is more even, with 60 percent falling between May and October. Throughout the entire Taiwan area, the driest months occur between November and February. EarthquakesTaiwan has a high degree of seismic activity due to its location at the junction of the Manila Trench and the Ryukyu Trench along the west side of the Philippine Sea plate. The collision of the two tectonic plates--the Philippine Sea plate and the Eurasia plate--which created the uplift of land that became Taiwan's four major mountain ranges, continue to push against each other. In addition, the Philippine plate has been forced beneath the South China Sea plate to the south. The majority of earthquakes occur off the coast of eastern Taiwan and are deep beneath the seabed causing little damage. Plate tectonics have created numerous fault lines that crisscross the island. The largest earthquakes in the past 100 years include a 7.1 magnitude temblor that killed more than 3,250 people in 1935, and a 6.8 magnitude quake on November 14, 1986, which killed 15 and injured 44. A powerful and devastating earthquake struck at 1:47 a.m. on September 21, 1999, toppling high-rise buildings, damaging roads and bridges, and severing powerlines across the island. The quake registered a magnitude of 7.3 on the Richter scale with the epicenter at Chichi township in Nantou County. More than 1,300 aftershocks were reported by the morning of September 22, with the strongest registering a magnitude of 6.8 in central Taiwan. According to statistics from the National Fire Administration of the Ministry of the Interior內政部消防署, as of December 30, 1999, the massive "921 Earthquake" caused the deaths of 2,415 people, injured 11,305, and left 29 still unaccounted for. The greatest number of casualties was in Taichung County with 1,175 dead and 6,190 injured. On October 22, 1999, another major earthquake occurred 2.5 km northwest of Chiayi City at 10:19 a.m., registering 6.4 on the Richter scale. Although there were no deaths, 122 were injured, ten buildings were severely damaged or collapsed. There were 37 cases of gas leaks, and 4 cases of fire. The release of tectonic energy in the aftershock area of the "921 Earthquake" continued in 2000. Three strong aftershocks with magnitudes of 5.3, 6.7, and 6.1 were reported in the area on May 17, June 11, and July 29, respectively. In addition, a strong earthquake with a magnitude of 6.2 occurred to the north of Hualien in eastern Taiwan on September 10.
Best viewed with Netscape 4.x or IE 5.x (medium font) at 800 x 600 True Color (32 bit) resolution |
||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
