Sundaland was a vast, ancient landmass that emerged during periods of significantly lower global sea levels. This region shaped the geography, life, and human dispersal across Southeast Asia. Its immense size and eventual submergence illustrate Earth’s dynamic past climate and geological processes. Understanding Sundaland provides context for the unique biodiversity and human history of the region.
Defining Sundaland’s Ancient Extent
At its maximum exposure, Sundaland encompassed a substantial portion of what is now Southeast Asia, extending from the Asian mainland. This included the Malay Peninsula and the large islands of Sumatra, Borneo, Java, and Bali. The region also encompassed the shallow waters that now form the South China Sea, the Gulf of Thailand, and the Java Sea, all of which were dry land.
The Sunda Shelf, Southeast Asia’s continental shelf, formed the geological foundation of this landmass. During the Last Glacial Maximum (LGM), around 20,000 to 26,000 years ago, global sea levels were around 120 meters lower than today, fully exposing the entire Sunda Shelf. Sundaland’s total area was 1.8 million square kilometers, roughly twice the size of India.
Ancient submerged river systems once flowed across this exposed land, connecting areas now separated by sea. These river channels and the Java Sea’s flat bottom provide evidence of Sundaland’s past as a low-relief land area. The western and southern boundaries of Sundaland were marked by the deep waters of the Sunda Trench and the Indian Ocean. Its eastern boundary was defined by the Wallace Line, a deep-water channel and significant biogeographical barrier.
The Geological Forces Behind Its Submergence
The disappearance of Sundaland was primarily driven by global sea level fluctuations tied to glacial cycles. During the Pleistocene epoch, from roughly 2.6 million to 11,700 years ago, Earth experienced repeated cycles of glacial expansion and retreat. When vast ice sheets accumulated at the poles and on continents, water was locked up as ice, causing global sea levels to drop significantly.
Conversely, as the climate warmed and these ice sheets melted, the stored water returned to the oceans, increasing sea level. The most recent major submergence of Sundaland occurred following the Last Glacial Maximum. Between 20,000 and 6,000 years ago, sea levels rose by 120 to 130 meters. This rapid rise progressively flooded the low-lying Sunda Shelf.
The shallow nature of the Sunda Shelf made it particularly susceptible to these changes. As sea levels rose, the extensive flat plains of Sundaland were gradually inundated, transforming it into the archipelagos seen today. This process was not instantaneous but occurred over thousands of years, with the final stages of submergence occurring between 8,000 and 6,000 years ago.
Sundaland’s Role in Human History and Biodiversity
Sundaland served as an important land bridge, facilitating early human dispersal across Southeast Asia. During periods of lower sea levels, this expansive landmass provided a pathway for human migration from mainland Asia into island regions. Research indicates that rapid sea level rises influenced human population movements, leading to segregation and forced migrations as land area decreased.
This region was also a center of rich biodiversity, supporting diverse ecosystems like tropical rainforests, swamps, and river systems. Its varied landscapes fostered unique flora and fauna, an evolutionary hotspot. The subsequent submergence of Sundaland impacted this biodiversity, leading to the isolation of populations and fostering speciation. Species that once shared a continuous habitat became separated, evolving into distinct forms on the new islands.
The Wallace Line highlights this biogeographical division, separating the Asian faunal realm from the Australasian. Islands east of this line, known as Wallacea, possess a unique mix of species, reflecting their isolation from Sundaland and Australia. This history shaped the diverse genetic makeup of human populations and the natural world in Southeast Asia.
Modern-Day Remnants of Sundaland
Despite its ancient submergence, Sundaland continues to exist as its higher elevation areas that remained above rising sea levels. The major islands of Sumatra, Borneo, Java, and Bali are remnants of this former landmass. These islands, along with the Malay Peninsula, represent the exposed Sunda Shelf.
The shallow seas that now separate these islands, such as the Java Sea and parts of the South China Sea, cover what were once terrestrial plains. The uniform shallow depths of these seas are a geological testament to the submerged continental shelf. These modern landmasses and surrounding waters continue to be studied, offering insights into ancient geography and climate change’s long-term effects on Earth’s surface.