Soil and the Environment - Soils for Fine Wines - page 11

Figure 1.6 Old vines growing in weathered schist in Languedoc-Roussillon, southern France.

Photograph by the author. See color insert.

Water carrying suspended rock fragments abrades surfaces. During transport,
rock material is sorted according to size and density and abraded, so that water-
borne or fluviatile deposits are characteristically smooth and rounded sand parti-
cles, gravel, pebbles, or boulders, depending on their size. Transport by water pro-
duces alluvial and terrace deposits. Figure 1.7 shows a young soil used for vines
in the Borden Ranch district near Lodi in California's Central Valley. This soil is
forming on gravelly alluvial material, probably representing two main phases of
active deposition, and is very freely drained. The larger fragments are either rolled
or bounced along the stream bed by a process called saltation . The smallest par-
ticles that remain in suspension are called colloidal . These require a long time to
settle and hence form sedimentary deposits only in deep, calm water (siltstones
and mudstones).
Ice was an important agent in the transport of rock materials during the 2
million years of the Pleistocene (box 1.2). During the colder glacial phases, the
ice cap advanced from polar and mountainous regions to cover a large part of the
land surface, especially in the Northern Hemisphere. The moving ice ground down
rock surfaces, and the “rock flour” was incorporated in the ice. Rock debris also
collected on the surface of valley glaciers by colluviation (see below). During the
warmer interglacial phases, the ice melted and glaciers retreated, leaving extensive
deposits of heterogeneous glacial drift or till . Streams flowing out of the glaciers
produced glaciofluvial deposits of sands and gravels in which the pebbles are less
smooth and rounded than in fluviatile deposits. Figure 1.8 shows an example of
a glaciofluvial deposit on top of older weathering granite near Calquenas in south-
central Chile. These soils are increasingly being used to grow wine grapes, although
maintaining the water supply to the vines can be difficult because of the soil's free
drainage.