InSAR satellite data revealed this 11th-century pagoda is sinking 2mm per year into compacting alluvial sediments. The differential settlement threatens structural integrity after 900 years.
Jasoneppink, CC BY 2.0, via Wikimedia Commons
A sinking city of temples
High above the plains of Bagan, satellites are watching the Shwesandaw Pagoda sink. This isn't a sudden catastrophe, but a slow, persistent process. Using a technique called Interferometric Synthetic Aperture Radar (InSAR), scientists can detect millimeter-scale changes in ground elevation from space. Data from satellites like TerraSAR-X shows that parts of the Bagan archaeological zone are subsiding. The Shwesandaw Pagoda, built in 1057 CE by King Anawrahta, is slowly descending into the very ground it has stood on for over nine centuries.
The problem lies beneath the surface. Bagan is built on a thick succession of soft alluvial sediments, deposited over millennia by the Irrawaddy River. These layers of clay, silt and sand are not as stable as solid bedrock. Under the immense weight of thousands of brick and stone monuments, these unconsolidated sediments slowly compact, causing the ground level to drop. This gradual sinking threatens the the 2,200 remaining structures in Bagan.
The danger of differential settlement
The sinking is not uniform. If the entire pagoda sank evenly, the structural stress would be minimal. However, the InSAR data reveals differential settlement. One part of the structure is sinking faster than another. This uneven movement creates immense shear and tensile forces within the ancient brickwork. For a 100-meter-tall structure like Shwesandaw, even a few millimeters of uneven settling per year can generate cracks and compromise the integrity of its five terraces and central stupa.
This non-invasive monitoring technique is a tool for cultural heritage preservation. By identifying which of Bagan's thousands of temples are most at risk, conservationists can prioritize their efforts. The data provides an early warning system, allowing for interventions before visible damage becomes critical. This is especially important in a seismically active region; the ground instability can worsen the damage from earthquakes, like the 6.8 magnitude event that damaged hundreds of Bagan's temples in 2016. The satellite data gives preservation teams a scientific basis for deciding where to focus limited resources, helping to protect this UNESCO World Heritage site from the combined threats of geology and time.
💡Fun Facts
The name Shwesandaw means "Golden Holy Hair," a reference to the sacred Buddha hair relics believed to be enshrined within the stupa.
Before the widespread adoption of Buddhism, the pagoda's terraces were guarded by statues of the Hindu elephant-headed god, Ganesha.
The original gilded *hti*, or ceremonial umbrella, that topped the stupa was dislodged during a major earthquake in 1975 and is now on display at the base of the pagoda.
Until 1957, the pagoda retained its original red brick appearance before being covered in white plaster and lime wash during a renovation.
