Rusukan Besar Island

Although relatively small in size, Pulau Rusukan Besar preserves an important geological history of western Borneo. Its marine erosion platform reveals distinctive joint and fault structures, manifestations of past tectonic activity that once shaped the Earth’s crust in this region.

Geologically, joints are straight fractures in rock without any displacement, while faults are fractures along which blocks of rock have moved under tectonic forces. On Pulau Rusukan Besar, these two structures intersect at right angles, forming a rare and distinctive box-like pattern known as tessellated pavement, a landform of grid-shaped fractures created by the complex interaction between joints and faults.

This structure not only reflects an active geodynamic history but also serves as physical evidence of Earth-forming processes that occurred millions of years ago. With its intersecting joints and faults, the island stands as a natural archive recording the pressures and strains once exerted within the crust of western Borneo.