The rice terraces in Sagada are sinking. Well, okay, not all of them but the ones that tourists usually view (see photo above) en route to SumaguingCave are. As yet, there has been no study to explain why this is happening so I can only guess that the river below the terraces has been eroding the foundation of the lower fields, and this naturally makes the whole terraces unstable. Geologists would have a better chance of explaining the problem and, hopefully, in coming up with solutions.
Incidentally, this problem is not limited to Sagada but is occurring in other parts of the Cordilleras. Ground subsidence and unstable ground hazards have also been reported in Pantikian, Balbalan, Kalinga and Butac, Natonin. It is also happening in the towns of Buguias, Mankayan and Atok, all in the province of Benguet. More information here and here.
A news and information blog on the Igorots/iCordilleras