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Soil Science
1.1.1 Introduction: the shape of the terrain
The origins of La Mandria, as with all the Padana Plain, date back to the last geological era, the quaternary, or approximately the last one million eight hundred thousand years. During the last period of the tertiary era, the Pliocene, a shallow, hot sea in slow retreat was located in the present site of La Mandria and the climate was much more stable without the glacial fluctuations.
The quaternary era is divided into two periods: the older, or Pleistocene period, and the more recent, the Holocene, that has lasted to the present day.
During the Pleistocene period, several dozen periods of glacial advance have been identified, or ice ages, defined due to the isotopic oceanic distribution of oxygen and identified by an increasing number (i.e. if “1” defines the current glacial stage, we have had glacial stages 2, 4, 6, etc.).
During some of the ice ages, the ice left the alpine circle, depositing materials that formed the morainic amphitheatres. This never happened with the ice of the Valli di Lanzo area, which, however, produced the abundant alluvial materials that make up the three-dimensional alluvial fan of the Lanzo Stura, formed by the considerable gradient change that is evident at the mouth of the valley where the channels tend to fan out.
Alternating long periods of erosion and short periods of deposition and accumulation in a context of regional rising and aggradation resulted in the dissection and terracing of the original alluvial fan. Currently, La Mandria Park includes the residual right edge of the great conoid detritus of the River Stura subdivided in various stages of terraces of the level surface largely preserved (vaude) but ridged by various erosive streams (low), often situated on early riverbeds, and separated by escarpments (banks) sometimes dozens of metres high.
It is possible to distinguish along the Stura the following orders of terraces: the current empty riverbed (imprudently also occupied by important production sites, the Lower Park), and lower ridge (Grange di Nole, Cafasse, Cirié, Venaria) sometimes defined as the primary level of the plain, an intermediate ridge (the current La Mandria and Vauda plateaus) and a high terrace conserved only in strips between Germagnano, Lanzo and Balangero on the left and La Cassa on the right, between 550 and 500 metres above sea level.
The evolution of the current Stura riverbed presents two notable characteristics: the left terrace has a uniformly sloping aspect with traces of many abandoned riverbeds while the right terrace is a severely-eroding escarpment. This tendency of the riverbed to move to the right, along with the symmetric movement to the left of the Sangone riverbed indicates a progressive sinking of the Turin plain due to neo-tectonic movement.
Finally, it is worth noting the transformation that occurred in recent years from an interlaced, multi-stream to a deeply embanked single stream; a transformation due, as has been noted, to the increased speed of the current which is in turn due to excavations in the riverbed and artificial embankments.
The muddy covering of the intermediate terraces shows typical cliff erosion, predominantly oriented toward the south or west, which breaks the monotony of the landscape and which, at times, confers on the lower walls a curiously asymmetrical formation.
