The ancient Inca city of Machu Picchu in Peru is in danger of being destroyed by landslides.

Japanese geologists have found that the earth beneath the ruins is shifting at an alarming rate. They say a major landslide could split the ruins in half at any time.

Machu Piccu was the last refuge of the Inca empire after it was overrun by Spanish conquerors in the 16th century. It is perched in the Andes mountains, 8,000 feet above sea level. American archaeologist Hiram Bingham discovered the ruins in 1911.

Researchers from the Disaster Prevention Research Institute at Kyoto University set up instruments to measure the rate of surface movement. They found that a section of the steep slope behind the ancient city was steadily moving downwards. Kyoji Sassa says that this is “a precursor stage of a rockfall or a rock slide. It’s not possible to say exactly when the landslide might occur, but that will be the focus of the next stage of our research.” He estimates that the landslide will be enough to destroy all of Machu Picchu.

The two-ridge structure of the site, with a concave dip in the middle and two slopes on either side of it, means that it could disappear in two stages. The west slope would collapse first, making the east slope and its ridge unstable. Then the second slope would follow.

Landslides are common in the area and the land on which the city was built is actually made of rocks from a previous landslide. “Usually such villages are constructed on landslide areas,” says Sassa. “Only landslide areas can supply water and soil for farming.”

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