Flagstaff, AZ – Earth Notes: Arroyo Cutting
Arroyos are a common sight on the Colorado Plateau. Most flow only briefly, carrying moisture from springtime snowmelt and summer monsoon storms. Yet even when dry they bear witness to very specific places and times.
Historical accounts and analysis of the soils, rocks, and organic matter moved by water show how arroyos change. An example is Oraibi Wash on the Hopi lands of northeast Arizona. It's a huge arroyo, up to 330 feet wide and 60 feet deep. Yet it probably grew that large in only three decades.
Tree-ring data show the area was wetter between 1906 and 1934 than at any time in the past seven centuries. Tremendous erosion resulted from a series of El Ni o weather patterns and from a lack of vegetation to absorb excess moisture.
The wash cut so deep it effectively ended an ancient practice called Ak-Chin [AHK-CHIN] irrigation on the alluvial floor of Oraibi Valley. The Hopi could no longer spread seasonal water from the channel onto their vegetable gardens. Impacts on traditional land use also were felt at Tolani Lake, where much of the sediment eventually piled up.
Arroyo cutting shows that cultural traditions thousands of years old can be changed dramatically by a climate shift lasting only a few decades a vivid reminder that an arroyo is a crack in the landscape. It separates not just what's on either side, but the past and the present too.