>> van tilburg: exactly.inwater and airborne seeds get into the pores of tuff, gradually breaking it apart. the wind whittles the stone away over time, and further damage is done by birds, and an organism called lichen. some moai are in worse condition than others. take a look at this one, called tukuturi. this photograph is from 1955, when it was unearthed. this is how tukuturi looks today. >> van tilburg: the stone breaks very easily. it is just not stable. >> cooper: essentially, i mean, they're dissolving. >> van tilburg: yeah, they are. i mean, if they're standing out in the rain, they're melting like sugar cubes. >> cooper: like sugar cubes in the rain? >> van tilburg: exactly. it's that dramatic. >> cooper: in the 1990s, with help from the japanese government, the 15 moai at tongariki, which had fallen or been toppled over, were reconstructed, along with the stone platform they now stand o. the u.n. has declared easter island a world heritage site, and efforts to slow the disintegration of the statues