The Siantu Lava Pillow Geosite is one of the most fascinating geological wonders in Belitong. It features a unique formation of pillow lava, a volcanic rock structure that looks like overlapping pillows. This special shape is created when hot basaltic lava flows into water and cools rapidly, forming rounded masses. The rock here is mainly basalt, rich in plagioclase and pyroxene minerals, along with traces of chlorite and calcite.
Scientists estimate that these rocks formed around 60 million years ago, during the Late Cretaceous period. In addition to pillow lava, the site also contains volcanic breccias—rock made of broken basalt fragments cemented together. Together, these features give us a rare window into the island’s deep geological history.
For researchers, Siantu is very important because it shows how magma from the Earth’s mantle once rose and interacted with surrounding rocks in a subduction zone. This process helped shape the foundation of Belitong, leaving behind basaltic rocks that tell the story of ancient tectonic and volcanic activity. The site also demonstrates the connection between volcanic rocks, granite, and metasedimentary rocks in the region.
For visitors, Siantu Lava Pillow is also a place of natural beauty and discovery. The unusual rock formations spark curiosity and make for unique photo opportunities. Standing here, you are literally on the surface of rocks that once flowed as lava beneath the sea millions of years ago.
By protecting and sharing the story of Siantu, Belitong adds another layer to its identity as a UNESCO Global Geopark. It is a reminder that beneath the island’s beaches and forests lies a dramatic history of fire, water, and shifting continents.