by Warren D. Allmon, Director, Paleontological Research Institution
Most wine is made from grapes of the species Vitis vinifera. This plant is native to the Mediterranean region, central Europe, and southwestern Asia, where it was used for wine production for thousands of years. Numerous species of Vitis are native to North America, but they are not preferred for fine wine production for various reasons, including high acidity, low sugar, and tough skins. Wine grapes were introduced to North America by European colonists during the seventeenth century, but the grapes fared poorly due to native diseases and insect pests, until they were hybridized with native grape species. Such hybrids were used for some successful wine production in Ohio and New York’s Hudson Valley in the early and mid-nineteenth century.
Vitis vinifera, the species of grape used in wine production. Image courtesy of Damiani Wine Cellars.
Wild Vitis vinifera prefers warm climates and very well-drained soil. Its many varieties and hybrids have different optimal growing conditions. Thus, concern for the right location for growing wine grapes centers on local environmental conditions. The French word terroir (pronounced tehr-WAHR) is generally used to refer to the complete natural environment in which a particular type of wine grape is produced, including factors such as the soil, topography, geology, and climate.
The climate in much of the northeastern U.S. is unsuitable for vinifera grapes because the winters are too harsh. Therefore the locations in the region where wine grapes can grow are generally those where temperatures are moderated, by topography and/or proximity to bodies of water. Within areas of appropriate local climate, wine grapes need deep, well-drained soils. This is why New York’s primary wine regions are Long Island, the Hudson Valley, and the Finger Lakes, all three of which have the right temperatures and the right soils.
There is a widespread but erroneous idea that geology affects terroir by contributing particular chemicals that make their way through the plant to the grapes and subsequently into the wine. This is reflected in some oenophile terminology, such as “minerality” or “shaleyness”, which implies that there is something in the soil that can be directly tasted in the wine. This is not true. Soil affects wine grapes by affecting plant physiology, mainly by controlling acidity (pH) and supply of water to the vines. The supply of both must be within a narrow range – neither too much nor too little. Soil pH is important because many nutrients are best absorbed at near neutral acidity (pH = 7). The amount and timing of water availability during the growing season and the soil water-holding capacity of the soils also play an important role. Vines obviously cannot grow without nutrients and water, but high levels of either can result in “excessive vine vigor”, that is, growing more leaves at the expense of fully ripening the fruit. Thus, it is soils that provide the right combination of acidity, nutrients, and water, under the right temperatures at the right times of year, that produce the best wine grapes and give them their particular qualities.
Geology of the Finger Lakes
What geological variables produce this narrow range of conditions, and why do they exist in the Finger Lakes region of New York? Geological conditions are produced by geological history, and the geological history of New York stretches back hundreds of millions of years, to when the region was covered by a shallow warm sea on the shores of a rising mountain range. That mountain range—called the Acadian Mountains, preserved today as the core of the Appalachians—formed when the continents that are now Europe and North America collided, beginning around 450 million years ago. These young mountains eroded rapidly, shedding huge volumes of mud and sand into the shallow ocean that then covered much of North America, including New York. All of the gray rocks visible at the surface across much of upstate New York, from Albany to Buffalo and from the New York Thruway to Pennsylvania, originated as this sediment that was deposited during what geologists call the Devonian Period, between around 420 and 360 million years ago.
Highly simplified reconstruction of the northeastern United States during the Devonian Period. Most of the rocks in the Finger Lakes Region were formed from sediments shed from the ancient Acadian Mountains into the Catskill Delta to the west. Image modified from original by J. Houghton first published in The Teacher-Friendly Guide to the Geology of the Northeastern U.S. by Jane Ansley (published by the Paleontological Research Institution) (CC BY-NC-SA 4.0 license).
The mud and silt formed rocks known as shale and siltstone. When erosion and deposition of these sediments ebbed, lime mud (calcium carbonate) that came mostly from the skeletons of marine organisms formed layers that would become limestone. The bedrock of much of upstate New York is therefore composed of alternating layers of shale, siltstone, and limestone.
Layers of Devonian siltstone (Moscow Formation) and limestone (Tully Limestone) can be observed at the Lower Falls at Taughannock Falls State Park, near the parking lot on Highway 89. Photograph by Jonathan R. Hendricks for PRI's Earth@Home project (CC BY-NC-SA 4.0 license).
Continued uplift after the Devonian caused the entire stack of layers to be tilted slightly to the south, which means that older layers are exposed to the north and younger to the south. Uplift also caused more stress and strain on these rocks, which formed numerous straight vertical cracks called joints, which are characteristic of many bedrock exposures in the region.
The vertical rock walls at gorges like Robert F. Treman State Park are so flat that they appear to have been cut by stoneworkers. Instead, they are formed naturally by cracks called joints. Photograph by Jonathan R. Hendricks for PRI's Earth@Home project (CC BY-NC-SA 4.0 license).
After the Devonian Period, sea levels fell, and New York State has not been widely flooded by the ocean since. No further marine sediment could accumulate, and so there are essentially no geological records for the next 360 million years.
Around 3 million years ago, global climates cooled and glacial ice began to expand in the Northern Hemisphere. Glaciers moved over Canada and the northern U.S. many times in a series of glacial and interglacial intervals. These ice sheets, which were probably a mile or more thick, sculpted the landscape over which they flowed, turning shallow, southward-draining river valleys into the deep, northward-draining Finger Lakes, two of which—Cayuga and Seneca—have bottoms below sea level.
Elevations of the Finger Lakes. Note that the bottoms of Seneca and Cayuga lakes are below sea level.
The region’s famous gorges were formed, not by the glaciers directly, but by streams eroding into the lake shores after the retreat of the ice.
These streams produced their own deltas which form the “points” that protrude into the lakes today. Some of these recently formed deltas are the sites of wineries. Thus, the combination of an ancient eroding mountain range, shelly marine life, and repeated glaciation and deglaciation have created a landscape of steep lake valleys dotted with gravel deposits draped over a deeply fractured bedrock.
The sloping land on the sides of the Finger Lakes were cleared of their native hardwood forests by Euro-Americans in the first half of the nineteenth century but were afterward found to be too steep for field crops. They were generally considered to be of limited value until it was recognized that they provided good conditions for growing grapes.
The slopes along the rims of the lakes enjoy both warmer minimum temperatures in winter and cooler maximum temperatures in summer. For example, the warmest region on the southeast side of Seneca Lake (known locally as the “banana belt”), the minimum temperature in winter is up to 5.1 °F warmer and the maximum temperature in summer is up to 2.1 °F cooler than areas away from the lake.
Satellite photo of the Finger Lakes region in the winter, showing the lesser snow accumulation caused by effects of warmer temperatures immediately around the larger lakes. Image from NASA (public domain).
Soil is the uppermost layer of the Earth’s surface in which plants grow, consisting of a mixture of minerals and organic matter. The mineral particles are derived from weathering and erosion of bedrock, both locally and far away. They vary in composition (for example, being rich in silica [SiO₂] or calcium carbonate [CaCO₃]), and in size (from the tiny particles that make up clay and silt to sand and gravel). Clays can also form in-place, during the breakdown of the original minerals. Soil mineral and organic matter composition affects nutrient supply and pH, which in turn affects nutrient availability.
Soil pH, a measure of soil acidity, is strongly affected by the bedrock from which the soil minerals were derived. On soils derived from limestones, rainwater (which is usually slightly acidic) will dissolve calcium carbonate, which buffers the pH of the soil, creating good conditions for nutrient availability and grape vine growth. On soils derived from siltstones and shales, the pH is lower and vineyard owners typically add ground limestone to the soil to raise the pH of the soil, which increases nutrient availability. Calcium carbonate transport through clay-rich soils is inefficient and slow therefore requiring higher amounts of lime addition to the soil.
A vineyard on Seneca Lake. Image courtesy of Damiani Wine Cellars.
This soil acidity pattern differs across the Finger Lakes region due to that slight southward tilt in the Devonian bedrock. Because there is less limestone in younger rocks in this stack, the limestone content of Finger Lakes soils decreases moving north to south, leaving less acidic soils (more conducive to high-quality vinifera grapes) to the north and more acidic soils to the south.
Grain size, in conjunction with soil organic matter, affects permeability and therefore drainage, as well as a soils capacity to retain water. These features, along with nutrient availability, are key to the suitability of soils for growth of all plants, including grape vines. In general, soils made up of primarily coarse-grained particles have greater permeability for water and therefore better drainage, but also have lower water-holding capacity and thus a more limited capability to supply water to plants. Finer-grained sediments, especially in the absence of organic matter, can reduce permeability and cause poorer drainage. Soils with a range of particle sizes balance the trade-off between too much (poor drainage) and too little (low supply) water. Ancient lake deltas generally have a different grain size distribution (and therefore different water-holding properties) than adjacent poorly-sorted glacial till or impermeable proglacial lake clays. Clay beds not far below the soil surface, resulting from either different depositional conditions or in-place formation, can come and go on a variety of spatial scales. All of this means that there can be dramatic changes in vineyard soil characteristics over very short distances and with locally sharp boundaries. Thus, within a single vineyard, or even a single field, drainage and water supplying conditions may vary significantly.
The Finger Lakes region’s bedrock matters to grape vines for yet one more reason. The roots of grape vines grow deep, and can reach 10 meters in length. The joints in the Devonian shale and limestone allow those long roots to penetrate deeply into the ground.
Soil at a vineyard on Seneca Lake. Image courtesy of Damiani Wine Cellars.
Thanks to Tara Curtin, Susan Riha, and Rob Ross for comments, and to Chelsea Steffes for editorial help.
Sources of More Information
Allmon, W.D., M.P. Pritts, P.L. Marks, B.P. Epstein, D.A. Bullis, and K.A. Jordan, 2017, Smith Woods. The environmental history of an old growth forest remnant in Central New York State. Paleontological Research Institution Special Publication No. 53, 208 p. Link.
Allmon, W.D., and R.M. Ross, 2007, Ithaca is gorges. A guide to the geology of the Ithaca area. 4th ed. Paleontological Research Institution, Ithaca, NY, 28 pp. Link.
Bloom, A.L., 2018, Gorges history. Landscapes and geology of the Finger Lakes region. Paleontological Research Institution Special Publication No. 55, 214 p. Link.
Figiel, R., 1995, Culture in a glass: Reflections on the rich heritage of Finger Lakes wine. Silver Thread Books, Lodi, New York, 53 p.
Figiel, R., 2014, Circle of vines: The story of New York wine. SUNY Press, Albany, NY, 194 p.
Meinert, L., 2018, The science of terroir. Elements. An international magazine of mineralogy, geochemistry, and petrology, 14(3): 153–158.
Meinert, L., and T. Curtin, 2005, Terroir of the Finger Lakes of New York. 18th Keck Geology Consortium Symposium Volume. PDF.
Swinchatt, J. 2012, Finger Lakes. A new-found source of great intrigue. The World of Fine Wine, 38: 60–67.
White, R.E., 2003, Soils for fine wines. Oxford University Press, New York, 279 p.
Wilson, J.E., 1998, Terroir: The role of geology, climate, and culture in the making of French wine. Mitchell Beazley, London, 336 p.