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When Continents Collide: How Wines are Affected by Plate Tectonics
By Wayne Belding
Apr 26, 2016
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The wines of Santorini have become rather well known in wine circles over the past decade.  The best Santorini whites of the Assyrtiko grape combine richness, complexity, texture and acidity in a balanced and exciting way.  Santorini is actually the name of a small 5-island archipelago, but the name is often used as a synonym for Thera, the largest island of the group.  We will use the Santorini designation for this column.

The Volcanic Cliffs of Santorini

One visit to the vineyards of Santorini and you will know that there is no other winegrowing region in the world quite like this.  Santorini is very new land in a geologic sense.  Its vines grow on the slopes of a volcano that erupted with cataclysmic force some 3500 years ago.  The violent eruption not only destroyed civilization on the island, but also wrought destruction far beyond the shores of Santorini.  The massive ash falls, pyroclastic debris flows, concurrent tsunamis and atmospheric shock waves likely caused tremendous damage throughout the Mediterranean, and the clouds of fine particles and sulfur that reached the stratosphere and probably caused the yellow fogs, reduced sunlight and cold temperatures observed in China at that time. Santorini today is a caldera, a remnant of the collapsed volcano that spewed billions of cubic feet of ash outward when it exploded.

Santorini Caldera from the Air

The geologic setting that is the cause of the volcanic activity is fascinating, indeed.  The earth’s surface is composed of plates that move, albeit slowly by human terms, and sometimes collide.  When they do, one plate generally overrides the other and, in the process, generates movements which we feel as earthquakes.  This subduction generates enough heat and surface fractures to form a conduit that allows the molten rock (magma) that lies deep beneath the surface to rise.  Once it reaches the surface, it forms a volcano.

Relative Plate Motion in the Mediterranean

In the Aegean Sea, we find the African Plate colliding with the large Eurasian Plate as well as the smaller Arabian and Aegean Plates.  As Africa plunges beneath the Aegean we see the resultant volcanic activity along a row of islands known as the Hellenic Arc.  Santorini has the most active history of the arc islands.  Immediately prior to its Bronze Age eruption, the island was a thriving community.  It was in Santorini that archeologists discovered the ancient village of Akrotiri, buried in Pompeii-like fashion by thick beds of volcanic ash that inundated the town.  Charred grape seeds and amphorae for storage found at Akrotiri indicate that winegrowing was part of life in this ancient community.  Pottery styles show that Santorini was part of the Minoan civilization based in Crete, some 70 miles to the south.  The devastation caused by the Bronze Age Santorini eruption is thought by many to be the cause of the Minoan civilization’s decline.

The Hellenic arc, including Santorini (Thera)

The geologic record shows that the volcanism that created Santorini has been active for 1-2 million years, depositing the volcanic rock assemblage that we see today.  The Bronze Age cataclysm of 3500 years ago is merely the most recent chapter in this long history.  Various eruptions have laid down porous beds of pumice and scoria hundreds of feet thick and those rocks are the basis of the vineyard lands we see today.

The soil of Santorini, known as aspa, is a mix of pumice, volcanic ash, scoria (porous solidified lava) and sand. The soil has little to no organic matter, but is rich in essential minerals, except potassium, creating wines with a naturally low pH level and high acidity.  The porous nature of the soil allows the earth to retain water, providing a reservoir for the vines during the dry season.  During the summer, rainfall is rare and the only source of water for the vineyards is the nocturnal fogs that envelop much of the vineyard area.  The vines retain the water that condenses from the fog and manage to survive the warm and sunny days.  Despite the low annual rainfall of around sixteen inches a year, Santorini vines are able to produce exceptional fruit.

Because the soil is so spare and sandy, Santorini is phylloxera-free and the plants can retain their original rootstocks.  The winds blow strongly throughout the year, so the vines are grown in the koulara method -- woven to form a basket shape that lays close to the ground.  After many years of such training, the nutrients must pass through several meters of vine to finally reach the fruit, which reduces the yields of these old vines.  As with most vines, the yields eventually drop too low to be economic.  At that point, ordinarily at 75 years of age or so, the baskets (ampelies) are cut off at the root.  New shoots will then emerge from the root and will be trained into a new basket.  For some vineyards, this process has been repeated multiple times, making the rootstocks hundreds of years old.

Basket-trained vines (ampelies) on Santorini

The positive side of the windy nature is that a cool northern wind (called meltemia) blows frequently from July through September, increasing the day-to-night temperature shift and helping the grapes maintain their characteristically vivid acidity.  Additionally, the constant wind helps to minimize problems with fungal diseases and reduces the need for vineyard treatments.  Consequently, most growers use organic methods simply because the climate eliminates the need for intervention.

Despite the sensational scenery, tending the vines in this environment is demanding work.  A severe earthquake in 1956 motivated many residents to leave the island and abandon vineyards -- the terraced remnants of which are still visible.  Today, there is an estimated 1400 hectares of vineyards still under cultivation, down from 2500 hectares fifty years ago.  Tourism has supplanted agriculture as the primary economic activity and few opt for the arduous work of tending vines.  There is hope, however.  As Santorini wines are recognized more widely for their distinctive character and high quality, there is optimism that winegrowing will stabilize and perhaps increase.  A sip of an amazingly complex and elementally refreshing Assyrtiko from Santorini will make fans of these delicious wines wherever wine lovers congregate.  The wines drawn from this geologically compressed and volatile continental collision zone are remarkable indeed.