Etna DOCs volcanic soils within the context of John Szabo’s “family of volcanic soils”

After our VinoMilo 2025 Roundtable (Volcanic Wines — The Contemporary Evolution of Volcanic Winemaking) where John Szabo, author of Volcanic Wines, was the featured guest, I wanted to see how well John’s characterization of volcanic soils mapped to the Etna reality. Towards that end, I borrowed a copy of the book from the Barone di Villagrande library (thanks Antonio) and re-read John’s foundational material.

John stipulates that there is no such thing as volcanic wine but hold to the position that there are volcanic wines. In the former case he is saying that there are no defined qualities that link all wines made on volcanic soils together: there is no volcanic wine. There are, however, wines made from grapes grown in volcanic soils; and these he calls volcanic wines. These wines, he says, “come in a radiant, infinitely nuanced rainbow of colors, tastes, and flavors.” 

John defines volcanic soils as “soils that formed from parent volcanic material” inclusive of lava flows, tephra, soils laced with volcanic ash, and soils that ended in valleys as result of gravity or alluvial activity. He places them into four broad categories:

• Especially young volcanic soils. These are formed on lava and “are more often rock than soil.” These soils have low water availability as enough time has not transpired for these soils to weather into water-retentive clays.
• Soils derived from ash, sand, and tephra. These soils also have a low clay content and tend to drain rapidly.
• Volcanic soils on hillsides. Gravity drains these soils quickly.
• Especially old, highly weathered volcanic soils. These soils have lots of clay and good water retention.

John sees the first three members of the family listed above as relatively infertile. Further, “semi-parched, semi-starved vines produce less fruit, smaller bunches, and thicker grape skins” which lead to “more deeply colored, concentrated, structured, and ageworthy wines with a broader range of flavors.” In John’s view, the stress imposed on the vine by water and nutrient “scarcity” produces the kind of fruit that results in high-quality wines. It should be noted that good drainage is not limited to volcanic-origin soils. Non-volcanics-derived sandy soils as well as chalk soils are also well drained. Soils on hillsides, especially if low in clay content, tend to be well drained whether volcano-derived or not.

The fourth member of this family grouping has better access to water but, according to John, when matched with a dry growing season, “keeps the vines moist, constrained, and able to focus on  even, steady ripening.

Let’s see where Etna soils fall within John’s described family of

volcanic soils.

Etna Soils

"All Etna soil rests on, or directly derives from, lava that flowed and hardened for thousands of years, along with ejected pumice, lapilli, and windblown volcanic ash" (Nesto and di Savino).

Historically, eruptive events at Mt Etna have been of the Strombolian style but occasional Hawaiian-style eruptions generate considerable lapilli fall on the flanks (The Strombolian and Hawaiian styles are described in the table below.). Large active volcanoes with the Etna eruptive style present some of the most complex soil-forming environments on earth (James, et al.).

Source: http://www.geology.sdsu.edu/how_volcanoes_work

Factors such as diversity in age and characteristics of volcanic materials, land surface morphology, local climate, vegetation, and land-use history all contribute to complex soil spatial patterns. In the profile dimension, complex soils result from intermittent tephra deposition, anthropogenic disturbance (in the case of Mt Etna, over 70% of the vineyards are terraced), erosion and subsequent deposition. According to James, et al., "soil profiles may reflect the amount and frequency of tephra deposition as much as 'normal' profile-forming soil processes operating on stable surfaces."

Landscape Formation
Volcanism in the Etna region began during the middle Pleistocene, at around 600 ka. The peak today stands at 3350 m elevation and the base is 40 km across. At elevations below 1100 m, lava varies in age from the 2014/2015 flow to the 500,000-year-old tholeitic basalts of a small area on the lower part of the southern flank (James, et al.). The terrain of historical (12th century to today) flows, as well as some pre-historic flows, is dominated by aa lava (basaltic lava with a rough surface, pahoehoe (basaltic lava with a smooth or billowy surface), and toothpaste (transition between aa and pahoehoe) morphology (James, et al.).

On Etna, depositive explosive activity from the summit crater is frequent with less frequent eruptions, often with higher effusive rates, from the flank vents and Strombolian activity from vents high on the volcano. The tephra varies in deposition rate and particle size with distance and direction from the source and accumulates unevenly on rugged lava surfaces. As an example, areas on the western and northwestern slopes of Mt Etna are barren rockscapes due to insufficient topsoil for significant vineyard development.

Soil Formation
As described above, volcanic activity of Mt Etna is both effusive (lava flows) and explosive (airborne ejection of pyroclastics). According to Nesto and di Savino, the lava flows create a patchwork of terroirs that is pertinent to any discussion of Etna contradas. Initial flows are barren rock pasteurized by heat which, after cooling, require hundreds of years to erode into soil and develop hummus, and, in so doing, become suitable for vines. The erosion product is sand rich in potassium and other minerals. Organic matter, created initially by the growth of micro-organisms (and later by plants and animals), results in rich, fertile soil.

But, according to Marco Perciabobco (Department of Agriculture, Sicily Region), soil parent material in the Etna environment is primarily pyroclastic (My prior post on volcanic soils detail the weathering of these materials). Weathering of this coarse-textured parent material, according to Marco, produces soils with an "aerated hypogeal (underground) environment and the following characteristics:

• Extremely well suited for the growth and development of vine roots
• Soil water stagnations are rare
• They warm easily (this generates stable conditions for the occurrence of the chemical reactions required for the weathering of the finest materials).

Soil Distribution
According to Perciabobco, the Department of Agriculture's soil survey dataset shows five different landscape systems in Etna: northern; northwestern; eastern; southeastern; and southern. The soils of these environments differ in the degree of weathering of the primary clay minerals. From north to south wetness decreases and so does weathering of the volcanic constituents. The soils of the northern landscape, when compared to the soils of the south, are finer textured, have a higher organic matter content, and a have a higher value of cation-exchange capacity.

I spent some time with Benjamin North Spencer (author, The New Wines of Mt Etna) to gain his perspective of the soils of the region. The sub-regions that Ben described were the Southwest, Southeast, East, Northeast, and North. A summary of his perspectives are contained in the chart following and additional clarifying information is provided in the text following the chart.

Southwest
The current surface that we see on Mt. Etna today is the Mongibello facade, consisting of material 15,000 years old and younger. That material overlays an earlier, much wider, shield volcano that has outcroppings in the extreme north and south of the Etna wine region. The material overlaying the shield volcano ranges from 10 to 100 m in depth and consists of recent volcanics: silica, lapilli (tephra of from 2 to 64 mm in size) rippidu, and bombs/blocks (effluvia greater than 64 mm in size are called bombs when molten and blocks when solid).

Southeast
This area has a massive fissure that flows up from the city of Catania to the central craters. According to Ben, there are 35 lateral parasitic craters that feed off the central plumbing. These craters form cones of sand and are endowed with pyroclastic that overlay on themselves. These cones have metal at the top and, as a result of gravitational erosion, a lot more silica and organically rich material at the plateaus. There is a wealth of rich organic material in the areas between the cones, as well as a lot of rich, black volcanic material.

This is a great place to grow grapes: all of the cones; all of the aspects that are presented; all of the different elevations ranging between 400 and 900 m. This is also the area that receives the largest amount of of volcanic sand from the regular eruptions of the volcano. Ben says that we are talking about 1500 lbs of fresh soil each year because of the way the winds spin around the volcano.

East
The Valle del Bove, the horseshoe-shaped structure that dominates on this side of the volcano, is, according to Ben, the original shield volcano's crater. This crater blew the top (15,000 years ago, according to Ben; 8,000 and 60,000 years according to other sources) off the mountain and then fell back in on itself. It collected snowfall from the mountain, forming a glacial lake, and decomposing the volcanics that were the core of the seven volcanoes that comprised the Elliptico. The eastern flank of the volcano was involved in a landslide and deposited water and eroded volcanics over the slope where we find Milo located today. These eroded volcanics were distributed over a very steep and plateaued environment.

Milo’s soil is sandy and of volcanic origin with a substantial portion of ripiddu (lapilli and eruptive pumice) intermixed with red soils from the Sahara Desert deposited here by the aforementioned winds. The sandy soils drain rapidly, forcing the roots to dig deep in search of moisture and nutrients. 

The EtnaDOC Consorzio recently introduced a new DOC map with 142 contrade, eight of which are located in the Milo comune. The map, with an exploded Milo section, is illustrated in the chart below and the physical characteristics of the contrade are illustrated in the chart immediately following.

Information sources: Ugo Nicosia (Marketing and Communications Director, Azienda Agricola Iuppa); communication with Brandon Tokash

Milo is the only area within the DOC where Etna Bianco Superiore can be produced.

Wines on the volcano's east are salty. According to Ben, the soils have a high mineral content but, in addition, breezes coming in off the sea are trapped at altitude and the salt moisture they contain come back to earth with the rain. These mineral, saline wines are endowed with incredible acidity and longevity and, if produced well, can age for 15 to 20 years.

Northeast
Overlying lava flows, most from the Mongibelo volcano. The soils are very fertile due to the rain softening the volcanics and mixing in the organics that fall out of the forests that sit above the DOC areas.

This area has a lot of exposure to the Alcantara Valley. It is exposed to the winds from the north that flow in between the volcano and the Nebrodi Mountains and to the Grecale in its southern reaches.

Steep slopes with great exposure to sunshine during the summer and at midday.

We start to see more international varieties here: Syrah, Chardonnay, Nero d' Avola. Softer tannins, more opulent fruit for the Nerello Mascalese here than for the same variety to the north. Also greater tropical notes.

North
As it relates to climate, my research shows that the Nebrodi Mountains offer some protection to the north slope of Mt Etna but some wind does make it over the top, bringing rain in the autumn and winter and moisture year-round. There are some benefits to this moisture though. The runoff, unlike the case for the runoff on the eastern and southeastern slopes, proceeds downhill at a moderate pace and is absorbed by the lava beneath the soil, This water store then becomes available to the vine roots during the growing season. The major beneficiary of this process is the area between the towns of Solicchiata and Randazzo. The wind from the northeast blows steam from the vents to the southeast creating a shadow which serves to reduce evaporation.

Ben sees the soils of the North as being very young and associated primarily with the current facade (15,000 years old and less). As a result of the youth of the volcanic deposits, the wines have great fruit, great structure, and longevity. The wines also have elegance, better acidity, minerals, and tannins, features that make them collectible. They are also delicious up front.

Ben sees a change in weather as you get up towards Rovitello. There is a dryness in the soil and old vines (100+ years) are planted on their own roots

As you move towards Randazzo, the growers are farming on an outcropping of the ancient volcano. The elevations here are a little lower. Ben says that you can see the interconnectivity between the vines, the old volcanoes, and, maybe, a little bit of limestone that has been pushed up by the tectonic collision between the African and Eurasian plates.

He sees the whites on this side as having a bit more intensity of fruit, more mature fruit, and saline mineral flavors with some tropical notes. The grapes here do not experience as significant a temperature shock as is the case in the previously visited sub-regions.

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Etna DOC appears to have every example of the family of soils described by John in his book and some. For example, the soils in Milo is a mix of eroded volcanics, new emissions, and dust blown i. from the Sahara Desert.

While the greater part of the family, as described by John, has infertile soils, the soils on Etna are moderately fertile. 

One area in which volcanic soils may be linked is an area not identified by John. Based on my research, the decomposition of volcanic material forms allophane, a type of primordial clay, which is sticky for nutrients and holds water temporarily so that it can be accessed by the vine roots. The allophanes, due to their construct, provide a much greater surface area for nutrient attachment than does other more traditional clays.

In future works I will continue to build out on the soil composition at the contrada level.

©Wine -- Mise en abyme