The Columbia Valley American Viticultural Area (AVA) of the Pacific Northwest, USA is the world’s largest officially recognized viticultural area with basalt bedrock. However, most Columbia Valley vineyards are planted in soils derived from thick loess and glacial flood sediments, rather than the underlying bedrock. Recently, vineyard plantings have expanded into parts of the AVA where basalt and basalt weathering products, derived either naturally or through mechanical ripping, are a major soil component. Tests were conducted to determine how the addition of a basalt component to soils could affect the terroir of Columbia Valley vineyards. To test for the chemical influence of basalt, samples were obtained from soils representative of the range of basalt influence and analyzed for iron content. Increases of 77% to 233% in available iron were observed in vineyards with basalt component relative to vineyards planted in grass-covered loess. To measure the thermal influence of basalt, temperature data loggers were installed within soils and grape clusters in basalt-covered and grass-covered vineyards. Temperature loggers in the basalt-covered vineyard recorded an 18% increase in average soil temperature at a depth of 5 cm, a 13% increase in average soil temperature at a depth of 25 cm, and a 4% in average cluster temperature relative to those in the grass-covered vineyard. Cluster temperatures in the basalt-covered vineyard were generally higher than in the grass-covered vineyard from late morning through early evening, equilibrating rapidly near sunset.
Author: K. R. Pogue
Department of Geology, Whitman College
345 Boyer Ave., Walla Walla, Washington 99362 USA
Email: pogue@whitman.edu
Keywords: basalt, terroir, soil, Columbia Valley