Southeast Asia is a fascinating mosaic composed of island groups, peninsulas and the mainland of Asia. The region is located on both sides of the Equator and almost entirely within the tropics. From time to time numerous immigrant groups have arrived in this area, giving rise to its extremely rich and varied culture, ethnology and history. Politically, Southeast Asia comprises the countries of the Philippines, Indonesia, Malaysia, Brunei, Vietnam, Laos, Cambodia, Singapore, Thailand, and Myanmar. Nearly two-thirds of the region is covered by seas.

Map of SouthEast Asia

Irrawaddy River, North Myanmar

Geologically, Southeast Asia has a stable core of granite and sedimentary rocks surrounded by a belt of volcanic and seismically active islands. The granite has given rise to rolling landscapes and steep hills such as the Main Range of Peninsular Malaysia. The sedimentary rocks have formed either high fold mountains such as to the north or plateaus and scarps as in eastern Thailand and West Malaysia. Plains in the interior are formed by a number of large rivers such as the Mekong, the Chao Phraya, and the Irrawaddy . In places, their courses are affected by fault systems and rock structures . The eroded material from these areas has built up scattered patches of coastal plains and deltas which at the mouth of large rivers such as the Mekong or the Irrawaddy have reached large dimensions.

Some of the seas such as the Malacca Strait and the South China Sea are shallow. For two million years, the earth underwent a series of glacial advances and retreats. When it was cold and the glaciers advanced, water was held up as ice in glaciers and the sea level dropped. During such glaciated times, large sections of the shallow seas of Southeast Asia became land. Plants and animals, and early humans migrated from the mainland to the islands. The other evidences of these times are the accumulation of tin deposits on land and offshore and nature of the coastal and offshore sediments.

Towards south and east, thousands of islands of various sizes form the countries of Indonesia and Philippines. The islands are volcanic and prone to earthquakes. The general relief pattern is that of a volcanic backbone or centre from which slopes fall steeply to the coastal plains. These volcanoes do not erupt much lava, but mostly spew out pyroclastics which are ash and other solid volcanic material. Pyroclastics are blown up bits of volcanoes. Fine ash from such pyroclastic eruptions may form large ash clouds on top of the volcano. Such ash may then circulate in the upper atmosphere cooling the temperature of the world a little that year. This happened in the 1991 eruption of Mount Pinatubo in the Philippines. Such eruptions can be huge, such as that of the Krakatau in 1883 which completely destroyed the volcano and killed thousands of people on the coastal plains mostly by drowning from tidal waves called tsunamis. Even bigger was the eruption of the ancient volcano of Toba . A huge lake was created where once this volcano stood. Pyroclastics tend to accumulate in river valleys radiating out of the volcanic cone. Subsequently, rain falling intensely on such material gives rise to mudflows which are called lahars. Both pyroclastic eruptions and lahars can be highly dangerous.

Merapi Volcano, Java, Indenesia

Mandalay, Myanmar

In general Southeast Asia has a hot and humid climate. Except for northern Thailand, central Myanmar, eastern Indonesia, and most of Indochina, the annual rainfall exceeds 2000 mm, locally rising to over 4000 mm. A significant part of the rain arrives in either of the two monsoons, the northeastern and the southwestern. The rain also falls with very high intensity. The destruction of the vegetation cover therefore leads to accelerated erosion and sediment transfer to the shallow coastal seas. Where the rainfall is pronouncedly seasonal and a large volume of sediment is present, the rivers are braided in appearance.

The natural vegetation for most of the southeast Asia is the rain forest with mangroves and other swamp forests along the coasts. A seasonal deciduous vegetation tends to occur in drier areas. Coral reefs are common in shallow offshore regions. Given the climate, the soils are generally not fertile except along rivers, in deltas and coastal plains , and on the volcanic slopes. Such areas are intensely cultivated.

Tanakeke Island, Southwest Sulawesi, Indonesia

Angkor, Cambodia

Southeast Asia has been populated for a long time. Evidences of early humans have been discovered in Java. Historical migrations and mixings and the level of civilisation and culture are reflected in a number of archaeological sites . The common agricultural practices are cultivation of rice and managing of plantations. A large part of the rain forest has been destroyed for timber collection. The industry ranges from handicrafts to electronics, although heavy industry is uncommon. Tin is mined over a large part, and offshore oil and gas fields are present.

The population of Southeast Asia is increasing and urbanisation is proceeding at a rapid pace. Cities have started to spread out on less desirable areas such as coastal swamps, steep slopes, and volcanic lands. Such cities also require resources such as clean drinking water and proper disposal of large volumes of wastes.Tourism is developing rapidly given the wide range of beautiful landscape and the fascinating cultural background of Southeast Asia. All this have given rise to a set of environmental problems. Some of the common problems are destruction of the rain forest, loss of soil fertility, loss of coastal swamps and mangroves and uncontrolled urbanisation. Southeast Asia, however, continues to be a fascinating part of the world both regarding the natural landscape and the cultural milieu.

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