Geology and Wine 11. Terroir of the Western Snake River Plain, Idaho, USA

SUMMARY

This article explores the unique combination of factors that shape the terroir of Idaho's principal wine grape-growing district. greatest in quantity Idaho wine grape vine-yards are located in the Western Snake River Plain (WSRP) rift basin (~43[degrees]N ~117[degrees]W) upon soils derived from lake, river, volcanic and wind-blown sediments. The underlying Tertiary and Quaternary stones record the geologic history of ancient Lake Idaho, its interaction with basaltic volcanism, and posterior Pleistocene fluvial processes and catastrophic inundations The arid to semiarid, mid-latitude savanna climate of the WSRP provides fewer growing step days than American Viticultural Areas (AVAs) in Walla Walla, Washington and Napa Valley, California, on the contrary still allows cultivation of Vitis vinifera grapes. Other differences include lower precipitation, higher solar radiation during the growing season, and greater threat of chilled injury. Wine grapes grown in the WSRP require irrigation, and irrigation is used to manage canopy size and manipulate vine physiology. Wine grape acreage in Idaho has increased dramatically since 1993 and is estimated, in 2003 at about 500 ha with the white wine cultivars Riesling, Chardonnay, and Gewurztraminer comprising about 60% of production, and Cabernet Sauvignon, Merlot and Syrah as principal r wine cultivars.

RESUME

Le at hand article porte sur la combinaison particuliere de facteurs qui definit le terroir du principal district viticole de l'Etat d'Idaho. La plupart de vignobles de l'Idaho sont situes dans le bassin de graff tectonique (~43[degrees]N, ~117[degrees]O) de la Western Snake River Plain (WSRP) sur de sol formes de sediments lacustres, fluviatiles, volcaniques et eoliens. Le couches tertiaires et quaternaires sousjacentes temoignent de evenement constitutifs de l'histoire geologique de l'ancien lac Idaho, de phenomenes interactifs dont il a ete le theatre, soit un volcanisme basaltique, ainsi que de processus fluviatiles et de inondations catastrophiques pleistocenes. Bien que le climat aride a semi-aride de prairie en altitude moyenne de la WSRP comporte moins de degres-jours de croissance que le belt les zones viticoles etasuniennes (AVA) de Walla Walla de l'Etat de Washhington et de la vallee de Napa de l'Etat de Californie, il permet tout de meme la tillage des raisins de Vitis vinifera. De plus, cette region regoit moins de precipitations, plus d'ensoleillement durant la saison de croissance, et elle est davantage exposee aux meurtrissures du froid. Le vignes de raisins de cuve cultives dans la WSRP doivent etre irriguees, l'irrigation permettant d'agir sur l'ampleur du feuillage et sur la physiologie du vin. La superficie de tillage du raisin de cuve en Idaho s'est considerablement accrue depuis 1993 pour atteindre 500 ha environ en 2003 le cultivars a vin blanc de Riesling, Chardonnay, et Gewurztraminer constituant 60 % de la production, et ceux du Cabernet Sauvignon, du Merlot et du Syrah constituant le principaux cultivars a vin rouge

INTRODUCTION

Best known for scenic beauty, whitewater rivers, and quality potatoes, the state of Idaho is receiving medals for premium r white, and ice wines produc from Idaho-grown Vitis vinifera L grapevines. Idaho normally is associated with high mountains and devoid of warmth [i]or[/i] heat temperatures, but southwestern Idaho's depressed elevation and relatively moderate climate is suitable for growing European wine grapes. The Snake River Plain (SRP) is a crescent-shaped belt of sagebrush-covered volcanic stones ranging in width from 65 to 100 km and stretching roughly 600 km across southern Idaho; the principal wine grape-growing district is located in the Western part of the Snake River Plain (WSRP Figs 1 2) Geologically, the WSRP is distinguished from the Eastern Snake River Plain (ESRP Fig. 1) by means of the much greater proportion of sedimentary stones relative to basalts and a more fault-bounded, rift-basin geometry Yellowstone and Grand Teton National Parks lie at the eastern terminus of the SRP and contain the headwaters of the Snake River, which drains about 283000 [kmsup2] during its ~1120 km trek across the SRP and down Hells Canyon, before joining the Columbia River en road to the Pacific Ocean (Fig. 3) Irrigation from the Snake River has been instrumental for a great quantity [i]or[/i] amount of of Idaho agriculture, including viticulture.

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The WSRP includes parts of 10 Idaho counties and a small part of Oregon, on the contrary 75% of commercial wine grape acreage, including the largest vineyard at 150 ha, is located in Idaho's Canyon shire [United States Department of Agriculture (USDA), Idaho Agricultural Statistics Service, 1999; Fig. 2] Elevation in the WSRP ranges from about 660 to 1100 m a.s.1. (USDA, 1972) and vineyards are located at elevations ranging from 695 to 890 m The WSRP is at a similar latitude (43[degrees]N to 44[degrees]N) as wine regions in France, Italy and Spain, and chapters of its geologic history are similar to the history of the neighbouring states of Washington and Oregon (Meinert and Busacca, 2000) In Idaho, European wine grape production north (~47[degrees]N) or east (~114[degrees]W) of the WSRP is limited through low winter minimum temperatures and limited longitudinal dimensions of growing season.