A foundation on the move
The hundreds of white and gold stupas that cover the Sagaing Hills are a sight, but the land they are built upon is in constant, unseen motion. The hills are a direct product of one of Southeast Asia's significant geological features: the Sagaing Fault. This massive right-lateral strike-slip fault runs for over 1,400 kilometers through the center of Myanmar, marking the boundary between the Indian Plate and the Sunda Plate. The two plates slide past each other horizontally at a rate of about 18 to 20 millimeters per year. This continuous movement builds stress in the Earth's crust, which is periodically released in the form of earthquakes.
The Sagaing Hills themselves are composed of metamorphic rocks, such as schists and gneisses, that have been pushed up by the immense pressure along the fault line. The fault is highly active, responsible for numerous historical earthquakes. Some ruptures along the fault have occurred at "supershear" velocities, meaning the speed of the fracture along the fault was faster than the seismic shear waves it generated, a phenomenon that intensifies ground shaking. The monasteries, some of which date back to the 14th century, are thus built on a area shaped and defined by powerful tectonic forces.
The chemistry of the sacred coatings
The brilliant white and gold that adorn the stupas are products of specific material science and chemistry. The gold is not paint, but incredibly thin gold leaf. In workshops near Mandalay, goldsmiths start with a small piece of gold and, through a multi-stage process of hammering, create sheaths of gold leaf just 0.000127 centimeters thick—thinner than the ink on a printed page. This process involves pounding small pieces of gold placed between layers of bamboo paper for hours until they become extraordinarily thin. Devotees apply these leaves to the stupas to gain merit.
The bright white coating on many of the structures is not modern paint; it is a traditional lime wash. This is a simple, effective coating made from slaked lime, or calcium hydroxide. When applied as a wash, the calcium hydroxide reacts with carbon dioxide in the atmosphere. This chemical process, called carbonation, converts it into calcium carbonate, or limestone, creating a durable and white surface that bonds to the stupa.
Another natural paste, thanaka, is a yellowish-white cosmetic made from ground tree bark and is a feature of Burmese culture. Often applied to the face, it provides protection from the sun and has a cooling effect. The active compound marmesin has been identified as a principal UV-blocking agent. The trees used to produce thanaka grow in the arid central regions of Myanmar, including the Sagaing area.