Cambodia

Relief

Cambodia’s landscape is characterized by a low-lying central alluvial plain that is surrounded by uplands and low mountains and includes the Tonle Sap (Great Lake) and the upper reaches of the Mekong Riverdelta. Extending outward from this central region are transitional plains, thinly forested and rising to elevations of about 650 feet (200 metres) above sea level. To the north the Cambodian plain abuts a sandstone escarpment, which forms a southward-facing cliff stretching more than 200 miles (320 km) from west to east and rising abruptly above the plain to heights of 600 to 1,800 feet (180 to 550 metres). This escarpment marks the southern limit of the Dangrek (Khmer: Dângrêk) Mountains. Flowing south through the country’s eastern regions is the Mekong River. East of the Mekong the transitional plains gradually merge with the eastern highlands, a region of forested mountains and high plateaus that extend into Laos and Vietnam. In southwestern Cambodia two distinct upland blocks, the Krâvanh (Cardamom) Mountains and the Dâmrei(Elephant) Mountains, form another highland region that covers much of the land area between the Tonle Sap and the Gulf of Thailand. In this remote and largely uninhabited area, Mount Aôral, Cambodia’s highest peak, rises to an elevation of 5,949 feet (1,813 metres). The southern coastal region adjoining the Gulf of Thailand is a narrow lowland strip, heavily wooded and sparsely populated, which is isolated from the central plain by the southwestern highlands.

Drainage

The two dominant hydrological features of Cambodia are the Mekong River and theTonle Sap. Rising in the Plateau of Tibet and emptying into the South China Sea, the Mekong enters Cambodia from Laos at the Khone Falls and flows generally southward to the border with Vietnam, a distance within Cambodia of approximately 315 miles (510 km). The Mekong is connected to the Tonle Sap by the Sab River. During the rainy season (mid-May to early October), the Mekong’s enormous volume of water backs up into the Sab and flows up into the Tonle Sap 65 miles (105 km) to the northwest, expanding the lake’s surface area from a dry-season minimum of 1,200 square miles (3,100 square km) to a rainy-season maximum of more than 3,000 square miles (7,800 square km). As the water level of the Mekong falls during the dry season, the process is reversed: water drains from the Tonle Sap back down into the Mekong, switching the direction of its flow. As a result of this annual phenomenon, the Tonle Sap is one of the world’s richest sources of freshwater fish.

Soils

Most of Cambodia’s soils are sandy and poor in nutrients. The so-called red-soil areas in the eastern part of the country, however, are suitable for commercial crops such as rubber and cotton. The annual flooding of the Mekong during the rainy season deposits a rich alluvial sediment that accounts for the fertility of the central plain and provides natural irrigation for rice cultivation.