Disappearing Act

March 1, 2001
Erosion, from the Latin word erodere, “to gnaw,” aptly describes the slow, steady pace of the natural phenomenon. Accelerated erosion – the kind we cause – is more like devouring than gnawing: a fast, violent rending of the land. Few examples are as dramatic as the microcosm of Easter Island.Dutch explorers reaching the South Pacific island in 1722 found a barren, eroding wasteland with sparse grass and shrubs, few inhabitants, and those mysterious, monolithic stone statues staring out to sea – a puzzle for the next two centuries. Not only who built them and why but, from the more practically minded, how did they move the darned things? Biologists and archaeologists have pieced together the island’s history, and the riddle of the statues is intimately linked with the island’s eroded slopes and treeless plains. Polynesian settlers arrived on the island around 400 AD and within a few hundred years began creating the immense heads and torsos, quarrying and carving the soft volcanic tuff and transporting the finished pieces up to 6 mi. before setting them on stone platforms along the coast. The statues averaged about 14 ft. tall – some as large as 40 ft. – and weighed around 14 tons. The largest was 82 tons.With enough people working together, archaeologists believed, the islanders could have moved the statues by dragging them along on wooden sleds; rolling them on logs; “walking” them along by tipping them from sides to side with strong ropes, much as you might move a refrigerator; or sliding them along well-oiled wooden runners. Every method proposed except one – a speculation in the 1960s that the islanders received aid from extraterrestrial visitors – would have required tremendous amounts of logs and rope. Yet the island has no large trees, few plants suitable for making rope – and certainly not in the quantities needed – and no oil-producing palms.Pollen analysis in the 1980s revealed a very different picture of the island’s early ecology. By boring out deep columns of sediment, researchers gained access to layer upon layer of ancient deposits of pollen grains. Radiocarbon dating determined the absolute age of each layer, and counting the grains revealed the relative abundance of each type of plant. A rich subtropical forest had grown there for millennia, including an 80-ft.-tall palm with an unbranched trunk – well suited to sliding statues along the ground. The abundant hauhau tree would have been ideal for making rope and the dense-wooded toromiro for firewood, as copious charcoal in the samples showed. Archaeological remains hint at a vast and complex society on the island, but the growing population and the demand for wood caused rapid, nearly total deforestation. The last palm fell by about 1400. Topsoil vanished; crops failed. As the trees disappeared, so did the birds that had nested in them, and with the birds went the plants they helped to pollinate. With steep coastlines and lack of coral reefs, the island offers little in the way fishing, and the birds were a major food source. Bones in the island’s refuse heaps show that the porpoise – which must be hunted at sea rather than from shore – was for generations another diet staple, but with no trees left large enough to build canoes, that food source was also lost. From a peak of perhaps 20,000 or more, the island’s population declined to about 2,000 at the time of the Dutch arrival. Some evidence – inconclusive – suggests the survivors resorted to cannibalism.Despite deforestation-borne flooding and mudslides we see so often today, it’s hard to imagine how, in such a short period, the islanders could have failed to understand the cascading effects and to anticipate the consequences – and alarming that they didn’t. The real mystery of Easter Island turns out to be much grimmer than it seemed