Dirt: The Erosion of Civilizations - Kootenay Local Agricultural Society

irch forest that covered thousands of square miles now occupies less than
3 percent of its original area.
Over time, herds of sheep increasingly disturbed the landscape. By the
start of the eighteenth century more than a quarter of a million sheep
roamed the Icelandic countryside. Their numbers more than doubled by
the nineteenth century. Visitors began describing Iceland as a bare land
devoid of trees. The combination of a deteriorating climate and extensive
overgrazing led to severe erosion and abandoned farms. Today, threequarters
of Iceland’s forty thousand square miles of land are adversely
affected by soil erosion; seven thousand square miles are so severely eroded
as to be useless.
Once Iceland’s slopes were deforested, strong winds blowing off its central
ice caps helped strip the soil from roughly half the once forested area
of the island. Large herds of sheep broke up the soil, allowing wind and
rain to dig their way down to bedrock last exposed by melting glaciers.
Soils built up over thousands of years disappeared within centuries. The
central part of the island where the soil has been completely removed is
now a barren desert where nothing grows and no one lives.
Some areas eroded soon after the Vikings arrived. During the relatively
warm period in the eleventh and twelfth centuries, before the Little Ice
Age, severe soil erosion caused the abandonment of mostly inland and
some coastal farm sites. Later erosion in the lowlands primarily involved
farms in marginal locations.
Many theories have been advanced to explain Iceland’s abandoned
farms. Inland areas have been vacated for centuries, some valleys literally
deserted. Until recently, the abandonment was primarily attributed to climate
deterioration and associated epidemics. But recent studies have documented
the role of severe soil erosion in converting farms and grazing
land into barren zones. The history of Icelandic soils can be read through
the layers of volcanic ash. Frequent volcanic eruptions imprinted Iceland’s
dirt with a geologic bar code. Each ash buried the soils onto which they
fell. The layers gradually became incorporated into the soil as wind
deposited more dirt on top.
In 1638 Bishop Gisli Oddson described layers of volcanic ash in Icelandic
soils. The observant bishop noticed that thick layers of ash separated buried
soils, some of which contained the rooted stumps of ancient trees. Since
Oddson’s day, it has been recognized that hundreds of volcanic eruptions
after the last glaciation produced fine-grained soils readily eroded if exposed
to high winds sweeping across the island. Windblown material accumulates
islands in time 225