CULTURAL RESPONSE TO CHANGING LANDSCAPES FROM THE ERUPTION OF SUNSET CRATER IN THE LATE 11TH CENTURY, NORTHERN ARIZONA, USA

Volcanoes bring risks and opportunities. Volcanic soils in temperate and tropical environments are commonly rich in nutrients and can be very productive for agriculture. In arid and semi-arid environments volcanic landforms weather and release their nutrients very slowly. However, the addition of eolian dust to the surface of basalt flows increases the concentrations of stored nutrients which remain in the soil for many thousands of years. In northern Arizona, the eruption of Sunset Crater in ~ AD 1075, deposited basaltic tephra on Pleistocene basalt flows in an arid climatic regime. The volcano displaced about 1800 people of the Sinagua culture who moved into the lower elevation arid areas and subsequently constructed large villages with multistoried, monumental architecture. Thousands of prehistoric agricultural features on lava flows attest to their use for food (corn) production. The features are associated with a layer of Sunset Crater tephra which provides a mulch to conserve soil moisture, allowing food production in areas where it was not possible prior to the eruption. Our research suggests the tephra contributed to decreasing soil pH which released valuable soil nutrients like P and N. Farmers who then came into the region were able to grow food for a burgeoning population. Soil physical and chemical properties show that farmed sections have lower nutrients, mixed soil horizons, and higher infiltration than unfarmed sections. It appears that these soils take more than 1000 years to regain the lost nutrients, mostly because the addition of eolian dust is so slow. Modern subsistence farmers can learn from prehistoric farmers that soils can readily supply nutrients but slowly recover, and a cover of stone mulch helps conserve soil moisture and allow for food production in marginal areas.