GEOLOGY OF THE SEAS
This map shows today's land areas as well as parts of the seas which were once land (Sundaland).
Malaysia's lands and seas form the northern part of Sundaland—an amazing geographical region stretching down to Java and across to Sumatra and Borneo. The region was once entirely land, but much of the lower lying central portion was drowned during a major rise in sea level which occurred after the last Ice Age. Thus, the islands and landmasses we see today were formed. Malaysia's seas—the Strait of Melaka and the South China Sea—lie on the Sunda Shelf. The depth of water over the Sunda Shelf is very shallow, less than 200 metres. This feature has given rise to unique ecosystems, and has also allowed the geology of the sea bed to be explored. Drowned valleys on the Sunda Shelf reveal that the area was once land, drained by rivers. The valleys often have paired terraces indicating that over time the sea level did not simply rise but fluctuated—rising and falling over the period before the last major inundation. In Malaysia, there is much evidence of these fluctuations, especially from the most recent rise, 5,000 years ago, known as the Holocene transgression. Geological data and coastal formations in Malaysia, such as marine notches, show that the mid-Holocene reached its maximum height around 5,000 years ago when the sea level was 5 metres above its present level.
Apart from physical features, such as drowned river valleys and beach ridges, core samples of rocks and sediments from the west coast of the Peninsula have been analysed. The findings reveal fossilized plant remains, such as pollen of different types of vegetation, from 10 metres under the current sea level to some kilometres inland of today's coastline where mangrove remains have been identified.
The basic outline of Malaysia was formed at the height of the Holocene transgression, but this original shape has been modified by the subsequent fall in sea level, by minor tectonic movements and, significantly, by coastal processes—the actions of tides and waves. Sedimentation and mangrove colonization have characterized large parts of the Malaysian coastline, especially around river mouths. In other areas, sandy beaches, spits and bars have been deposited by the action of the waves. In other places, again depending on the action of the waves, beach deposits and cliffs are being eroded and material transported along the coast. In fact, the evolution of the country's coastline is continual. In recent times, the hand of man can also be seen in the configuration of the coastline. Development close to the sea shore has exacerbated erosion in some areas; groynes and breakwaters have had some positive impacts but also interfered with the natural longshore drift process, ultimately causing unwanted build-ups of sediment; and mangroves have been destroyed exposing areas to erosion. Malaysia now has regulations prohibiting development too close to the high tide mark and people are realizing that often the cheaper and less destructive approach is to work with nature rather than against it. A clear understanding of geomorphological processes becomes vital in determining how future development can best take place.