Dirt: The Erosion of Civilizations - Kootenay Local Agricultural Society

When asked how the great stone statues had been transported, the few
remaining islanders did not know how their ancestors had done it. They
simply replied that the statues walked across the island. For centuries the
bare landscape fueled the mystery of the heads. No one, including the
sculptors’ descendants, imagined that the great stone statues were rolled on
logs—it seemed just as likely that they had walked across the island on
their own.
Many of the statues were left either unfinished or abandoned near their
quarry, implying that their sculptors ignored the impending timber shortage
until the very end. As timber became scarce, competition for status and
prestige continued to motivate the drive to erect statues. Even though the
Easter Islanders knew they were isolated on a world they could walk
around in a day or two, cultural imperatives apparently overcame any concern
about running out of trees.
European contact finished off what was left of the native culture. In the
1850s most of the island’s remaining able-bodied men, including the king
and his son, were enslaved and shipped off to Peruvian guano mines. Years
later, the fifteen surviving abductees repatriated to their island introduced
smallpox to a population with no immunity. Soon thereafter the island’s
population dropped to just one hundred and eleven, unraveling any remaining
cultural continuity.
The story of how Easter Islanders committed ecological suicide is preserved
in the island’s soil. Derived from weathered volcanic bedrock, thin
poorly developed soil, in places only a few inches thick, blankets most of
the island. Just as in other subtropical regions, the thin topsoil held most
of the available nutrients. Soil fertility declined rapidly once vegetation
clearing allowed runoff to carry away the topsoil. After that only a small
part of the island remained cultivatable.
Distinctively abbreviated subsoil exposed at the ground surface testifies
to erosion of the island’s most productive soil. Exposures at the foot of hillslopes
reveal that a layer of material brought down from higher on the
slopes covers the eroded remnants of the older original soil. These truncated
soil profiles are studded with telltale casts of the roots of the now
extinct Easter Island palm.
The relationship of soil horizons to archaeological sites reveals that most
of the soil erosion occurred after construction of stone dwellings (ahus)
associated with the rise of agriculture on the island. These dwellings were
built directly on top of the native soil, and younger deposits of material
islands in time 219