A Pliocene river of stone
On the eastern bank of the Irrawaddy River, near the town of Singu, a wall of dark, geometric pillars rises from the landscape. These are the Singu Basalt Columns, the eroded remains of a volcanic eruption from the Pliocene Epoch. The columns are the product of a geological process called columnar jointing. When a thick flow of basaltic lava cools, it contracts horizontally. This contraction creates tensile stress, which is relieved by the formation of cracks. As the lava cools uniformly, these cracks propagate downwards from the surface, forming a remarkably regular network of polygonal, often hexagonal, columns.
The lava that formed these columns originated from the Singu Plateau, also known as Letha Taung, a volcanic field covering approximately 100 square kilometers. This eruption occurred during the Pliocene, between 5.3 and 2.6 million years ago, pouring a sheet of fluid basalt over the existing Mio-Pliocene sandstones of the Irrawaddy Formation. The Singu lavas are classified as basaltic trachyandesite and alkali basalt. Their chemical composition shows they are intraplate basalts, meaning they formed far from the tectonic collision zones that typically produce volcanic activity. Instead, the eruption likely occurred along fissures associated with the active Sagaing Fault, a major transform boundary that runs under the region.