One of the most profound influences on many of the winegrowing regions we revere today is the direct and indirect action of glaciers. Winegrowing regions at high latitudes often exist because the local microclimate is warmed by a large body of water, either a lake or river. In a multitude of instances, glaciers are the reason for those impacts.
Our world has been locked in ice for most of the past two million years. When measured against a human’s lifespan, that’s a long time but it represents only 0.0004 percent of the earth’s 4.5 billion year history. If you compressed the earth’s history to the span of a single day, two million years is equivalent to the last 35 seconds of that span. Thus, the glacial activity of the most recent epoch (the Pleistocene, in geologic parlance) is very recent in geologic timescale terms.
Massive glaciers covered the land mass of the northern hemisphere until their most recent retreat around 12,000 years ago. When I say massive, I mean MASSIVE! Think of it, ice up to ten thousand feet thick covering all of Canada and extending as far south as Cincinnati. An ice mass this large in motion, however slowly, exerts immense force on the land surface beneath. It has the power to gouge broad valleys hundreds of feet deep. When so much of the earth’s water is in solid form as glaciers, the sea level throughout the world dropped nearly four hundred feet, creating much broader continental landmasses than exist today.
Extent of North American Ice Sheet
Mountainous areas beyond the reach of the continental glaciers developed their own ice sheets during the Pleistocene as well. The Alps, Pyrenees, and Massif Central of France all contained thick masses of ice that moved from higher elevations to lower.
Glaciers advance when the weather is cold and more snow is added in a year than melts. When the climate changes and the rate of melting exceeds the additions of new ice, glaciers recede. Although the recession process is not marked so much by ice movement, it does have a profound effect on the landscape in the form of meltwater -- massive amounts of meltwater in many cases. Glaciers do not recede at an even, measured pace. They often alternate advances with recessions, repeating the flooding meltwater process over and over. In all cases, glaciers affect the drainage of the land significantly. All of the debris pushed in front of the glacier as it advanced is simple left as a pile of dirt -- a moraine to geologists. Similarly, the ground up rock and sediment carried by the ice behind the leading edge of the glacier is dropped onto the ground where the glacier melted, giving a haphazard mix of lakes and hills and swamps.
How does all this ice affect the winegrowing regions we know? Throughout the world, lakes inhabit ground that has been gouged out by glacial movement and filled by meltwater as the ice retreated. In the United States, the most significant example is the Great Lakes. These are among the earth’s largest lakes and were carved by the action of the Laurentide Ice Sheet. The lakes provide a significant moderating influence on the climate of the surrounding land masses. Thus, even at a far northern latitude, the Leelenau and Old Mission Peninsulas of northern Michigan support vineyards that consistently produce high quality Rieslings and other varieties. The vineyards of Ontario’s Niagara Peninsula owe their existence to the warming effect of Lake Ontario as well.
Old Mission Peninsula, Michigan
On a smaller scale, the glacially carved Finger Lakes of New York offer the same moderating influence and the burgeoning wine industry on Lakes Seneca, Cayuga, Keuka and more are evidence of this moderation. In New York as well, vineyards are planted along the glacially-carved estuary of the Hudson River. Long Island represents the terminal moraine of the ice sheet -- a pile of morainic debris that is the home of vineyards on the North Fork of Long Island.
Lakes Ontario, Erie, Huron and Finger Lakes
Moving west of the Great Lakes on the North American continent, we find that vineyards thrive on the shores of Lake Okanagan in British Columbia for the same reason. The moderating influence of the deep, glacially gouged lake allows grapes to ripen effectively and consistently. One of the newest AVAs in the United States is Lake Chelan in Washington State. It was a similar glacial process that carved the 1400 foot deep lake and allows this large volume of water to moderate the temperatures of its adjoining vineyards.
In Europe, we find that direct glacial action has created the landforms and/or the large bodies of water that affect winegrowing areas. The large lakes of northern Italy are all remnants of glacial action. Lake Maggiore alters the climate in a positive way for the DOCGs of Ghemme and Gattinara, among others. The best vineyards of Franciacorta sparkling wines rest on the terminal moraine left by the glacier that sculpted Lake Iseo. So too, the glaciers that dug out the basin of the deep Lake Garda provided the vineyards of Bardolino and Bianco di Custoza with a mild enough climate for bountiful viticulture. Similar to Franciacorta, the vineyards of Lugana are located on the terminal moraine of the glacier that created Lake Garda.
The Lake Country of Northern Italy
It is not just lakes that are evidence of the viticultural influence of glaciers. The slopes along the Adda River of Lombardy are covered with the lateral moraine of the glacier that moved through the valley. These glacially deposited soils now support the Nebbiolo vineyards of the Valtellina Superiore. Similarly, glaciers that carved the valleys of the Valle d’Aosta and Alto Adige left behind today’s vineyard soils as they melted.
Valtellina vineyards on Glacial Soils
Outside of Italy, the active forces of glaciers carved the basin of Lake Geneva (Lac Léman). The broad slopes on the north shore of the lake, especially at the villages of Dézaley and Calamin, offer the ripest Chasselas grapes due to the reflected light and moderating influence of the large lake. The Bodensee (Lake Constance) on the French-German border owes its existence to glacial action as well. Here are some of the warmest vineyards in Germany, often planted with Spätburgunder and other red varieties that require extra heat.
That is just an overview of winegrowing areas directly formed by ice action. There are glacial impacts that are exhibited well beyond the ice boundary as well. These periglacial phenomena have influenced an even broader range of vineyard areas. Those will be the subject of future articles.