What’s the Way a Sphinx Crumbles?

Eric Doehne’s most notable skill is his talent for watching things fall apart. It’s an invaluable asset in his research into how to slow the deterioration at ancient sites from Central America to Africa.

Many of the world’s most treasured cultural sites are now imperiled. In Egypt, the exquisite 3,200-year-old paintings in Queen Nefertari’s tomb are flaking and cracking. The Great Sphinx, built 4,600 years ago and an icon of Egyptian civilization, is slowly but relentlessly disintegrating. In Belize, an ancient Mayan city is crumbling.

But how does one save a monument the size of a Mayan pyramid? How do you protect a site in a desert or damp tropical forest that cannot be moved inside a museum?

Doehne, a 34-year-old geologist at the Getty Conservation Institute in Los Angeles, says solutions can’t be found to preserve the world’s monuments and artifacts until scientists get a better idea of precisely what imperils them.

“You have to understand how things fall apart before you can learn how to preserve them,” he says.

Doehne does this by studying a monument’s deterioration at the scale at which it takes place. Things crumble not chunk by chunk, but grain by grain. To find out what makes a pyramid crumble or a Sphinx flake, Doehne examines tiny pieces of such relics under an environmental scanning electron microscope.

In his lab at the Getty, he places a piece of limestone smaller than the tip of a needle into the chamber of the scope. Magnified 50,000 times, the limestone resembles small-curd cottage cheese.

Doehne makes a more scientific observation. “What we’re looking at are salt crystals,” he said.

While pollution, vandalism and war threaten to destroy historic sites that have endured for millenniums, in some instances the gravest threat is the breath of a tourist.

When a lot of tourists are in a confined space, they create a lot of moisture. Many rocks act like sponges, soaking up that moisture, which then interacts with salts present in the rock, forming crystals.

To study the problem, Doehne has made several videos. But don’t expect his documentaries to air on PBS or the Discovery Channel. One video, which he thoughtfully shows at high speed, shows salt crystals forming over a two-week period on a column of limestone.

One solution, Doehne says, is to protect sites by keeping the humidity and temperature relatively constant. That’s a difficult task in tropical climes such as Belize, where it rains more than 25 feet a year. Scientists use biocides to control the growth of harmful flora. Sheds protect some of the Mayan structures from rain. But many governments feel they can’t afford to limit access to popular tourist sites and are reluctant to cover a national symbol like the Great Sphinx under a giant tent.

When adequate solutions can’t be found, Doehne sometimes recommends that sites be reburied. For instance, on a remote savanna in northwestern Tanzania at Laetoli are 70 footprints preserved in hardened volcanic ash from some of mankind’s earliest ancestors. The endangered prints, which have since been reburied under a protective layer of synthetic fabric.

It’s not just other countries’ cultural treasures that are in trouble. Bird droppings harm the Lincoln Memorial, and pollution--one of the most serious problems facing cultural relics worldwide--threatens the Washington Monument. “It would be less expensive to lower air pollution rates than to protect each separate site,” Doehne said.