Geoscientist Online

Jenny Huggett* admires some rocks - and the odd beaded bubble – among the developing wine-growing industry of the Eastern Mediterranean.

Geoscientist 22.03 April 2012

Exactly where wine was first made is lost in the mists of time, but archaeological research has confirmed that the blushful Hippocrene has been made in the Eastern Mediterranean since around 3200 BCE. Although the spread of Islam from the 6th Century CE onwards diminished demand, the Christian communities of the region have kept wine culture alive. An exciting new project to create a wine museum of the Levant in Lebanon’s Bekaa Valley will include a substantial section on the geoviticulture of the region; and it was this that led me out there.


The climate of the upland regions of Lebanon is particularly well suited to winemaking, with almost continuous sunshine in the summer, and heavy rainfall from late autumn through early spring to recharge the aquifers. Most vineyards are in the Bekaa Valley, where temperatures are typically ten degrees cooler than at sea-level; though in summer they still hover around a scorching 35°C.

TERROIR

Factors linked to geology that influence wine quality are water availability, nourishment and topography. The much-abused term ‘terroir’ approximates to the sum of these factors, together with aspect and climate.


Lebanon is divided into three main geological and topographic units: the Mount Lebanon range, which rises from the sea to 3083m, the Bekaa Valley, which despite the name lies at 800-1200m, and in the east, the Anti Lebanon range, with its highest peak at 2814m. The country’s geological structure consists of two large NNE-SSW trending anticlines (the two mountain ranges) separated by a large syncline (the Bekaa). The Yammouneh Fault, the northern continuation of the Dead Sea transform fault, is responsible for dramatic slopes on the western margin of the Bekaa Valley.

Most of Lebanon comprises lower to middle Cretaceous sandstones and limestones, though early Jurassic limestones occur in the cores of the anticlines, and the southern up-thrust of the Yammouneh Fault. In the Early Tertiary, folding uplifted the Mesozoic rocks as Arabian and African plates collided. The sea retreated from the Bekaa depression, and Miocene-Pliocene conglomerates and lacustrine limestones were deposited. In the Pleistocene, the Bekaa was sporadically submerged beneath a large lake. In the last 10,000 years as the climate has warmed up, the lake has receded leaving rich fertile soils that have been farmed since the dawn of agriculture.

The limestones of the Mount Lebanon range extend north into western Syria and south into Israel and western Jordan. Extensive basaltic plateaux (of probable Miocene age) spread across much of central Syria, and to the south into Jordan.

TERRA ROSSA

Throughout the region the soil on limestone is terra rossa, the classic Mediterranean climate soil of limestone areas. This largely comprises the limestones’ insoluble residue, with a highly variable proportion of loess (sand blown from North Africa and Arabia) and rock fragments. Almost mystical properties are attributed to the perceived richness of this soil, here and in other parts of the world, such as the Coonawarra of South Australia. There is no clear reason why terra rossa should yield better wines that other soils; perhaps the significance is that terra rossa is only associated with the Mediterranean climate.

Most soils contain all the chemical nutrients that vines require for healthy growth in abundance. However on soils rich in organic matter, vines grow fast and the fruit lacks intensity of flavour. This is why quality wines are grown on what are described as ‘poor’ soils, though they are only deficient in organic matter, and not the elements derived from rock.

What is apparent from the Bekaa Valley is that the best wines are made on shallow, stony terra rossa soils poor in organic matter. Soils that fit this pattern occur close to the western margin of the plain, and on outliers of limestone and conglomerate in the valley. Higher up the slopes there is almost no soil at all, while in the deep, also rubified, alluvium of the central part of the valley there is so much humus that it is better suited to growing potatoes than vines.

The ideal scenario for viticulture is a high porosity low permeability rock overlain by a well drained soil. This is particularly true where rainfall is highly seasonal, as in Lebanon and western Syria. Vines hate to have their roots water-logged; they need good drainage, which is easily achieved by a balance of sand, clay and rock fragments in a soil overlying porous rock. A rock of fairly low permeability has the advantage that the water table does not become excessively lowered during the summer months. Although the Mesozoic limestones of Lebanon, Syria and Jordan are fairly well indurated, deep karstic weathering and faulting allow water to percolate deeply.

WATER

In the past it could be said that Lebanon’s greatest natural resource was water. However excessive abstraction here and elsewhere in the region has resulted in the water table being lowered by as much as 100m. In the mountains of western Syria, (Cenomanian-Turonian limestone and dolomite) the water table now lies at 250m, while in the Bekaa Valley it is at 150m depth.

The wholly organic vineyards owned by the Saadé family - Bargylus in western Syria and Marsyas in the Bekaa - are both on karstified limestone with a stony terra rossa soil 30-100cm thick. In these vineyards the young vines are encouraged to root deeply by planting, between the rows, crops that tend to open up fractures in the deeply weathered rock immediately beneath the soil. This has successfully avoided the need to irrigate vines over two years old - a practice that will become more common as water becomes ever scarcer. Excellent wines are also made on the geographically lowest portion, of the east-facing slopes of Kimmeridgian limestone in the Bekaa Valley. Here the soils are very stony and produce well structured wines that are less full-bodied than those grown where the soil is deeper.

In Jordan the St Georges vineyard has been planted fairly recently by Omar Zumot. He freely admits that many thought he was crazy to do so, but his wines demonstrate otherwise. He has planted two areas - one on basalt on the northern border with Syria, the other on Cenomanian limestone close to Madaba, where wine was made in Biblical times.

The basalt landscape is desert, with around 75mm rain/year, and a water table at 300m, from which water is pumped to irrigate the vines (vines cannot survive here without irrigation). The soil however is 5-7m deep, stony (due to inclusion of limestone from the surrounding Cretaceous hills) and rich in inorganic nutrients derived from the basalt. This soil is much more clay-rich than the terra rossa, a fact that is undoubtedly advantageous in this climate as the clay can absorb what little rain may fall, and hold it in for longer. Typically for basalt soils, the clay is smectite. This is further good news for the vines as smectite gives up its interlayer cations to nutrient seeking plants more readily than do other clays.

Further reading – acknowledgement

For further information on the geology of Lebanon see the excellent documents by Chris Walley readily available on the Internet. He is thanked for permission to use the map featured here.

* Dr J M Huggett, Petroclays, The Oast House, Sandy Cross Lane, Heathfield, Sussex TN21 8QP United Kingdom. E: [email protected]