MACHU Picchu, the ancient Incan stronghold in the Peruvian Andes, is in
imminent 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 two at any time.
Machu Picchu was the last refuge of the Inca empire after it was overrun by
Spanish conquistadores in the 16th century. Perched in the Andes 2550 metres
above sea level, the city is built on two ridges on a spur, with a gentle
鈥渇ront鈥� slope on the eastern side and a steeper 鈥渂ack鈥� slope on the west side.
American archaeologist Hiram Bingham discovered the ruins in 1911 and UNESCO has
listed the city as a World Heritage Site.
Researchers from the Disaster Prevention Research Institute at Kyoto
University set up 10 extensometers to measure the rate of surface movement. They
found that one section of back slope was moving downwards at a rate of up to 1
centimetre per month.
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鈥淭his is quite fast, and it鈥檚 a precursor stage of a rockfall or a rock
slide,鈥� says Kyoji Sassa, who recently presented his findings at a Tokyo
symposium organised by UNESCO. 鈥淚t鈥檚 not possible to say exactly when the
landslide might occur, but that will be the focus of the next stage of our
谤别蝉别补谤肠丑.鈥�
Sassa estimates that the landslide will be around 100 metres deep, enough to
destroy all of Machu Picchu. The two-ridge structure of the site鈥攚ith a
concave dip in the middle鈥攎eans 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 (see Graphic).
Landslides are common at Machu Picchu, and the spur on which the Inca citadel
rests is actually made of rocks from a previous landslide. 鈥淯sually such
(mountain) villages are constructed on landslide areas,鈥� says Sassa. 鈥淥ther
parts aren鈥檛 suitable, and only landslide areas can supply water and soil for
蹿补谤尘颈苍驳.鈥�
Sassa discovered that small rockfalls and deformations have already damaged
the structures at Machu Picchu. There is a distortion line running north-south
inside the citadel and buildings along the line show signs of damage. A popular
lodge and cafe had to be repaired after suffering structural damage because of
subsidence.
As well as determining when a catastrophic landslide might occur, the Kyoto
university researchers hope that future studies will help them work out how to
avoid the impending disaster.