The Pietra Alta (in

piedmontese Piedmontese (; autonym: or , in it, piemontese) is a language spoken by some 2,000,000 people mostly in Piedmont, northwestern region of Italy. Although considered by most linguists a separate language, in Italy it is often mistakenly regard ...

: ''Pera Aota'' or ''Peraota'', meaning ''High Stone'') is a

glacial erratic A glacial erratic is glacially deposited rock differing from the type of rock native to the area in which it rests. Erratics, which take their name from the Latin word ' ("to wander"), are carried by glacial ice, often over distances of hundred ...

in the

comune The (; plural: ) is a local administrative division of Italy, roughly equivalent to a township or municipality. It is the third-level administrative division of Italy, after regions ('' regioni'') and provinces (''province''). The can also ...

Caselette Caselette is a town and ''comune'' in the Metropolitan City of Turin, in the Piedmont region of northern Italy. It is located at the entrance of the Val di Susa, from Turin, at the foot of Monte Musinè. It is home to the Castle of the Cays Co ...

( TO, Italy), relevant for its size and its isolated location.

Features

The erratic is a massive boulder with a

pyramid A pyramid (from el, πυραμίς ') is a structure whose outer surfaces are triangular and converge to a single step at the top, making the shape roughly a pyramid in the geometric sense. The base of a pyramid can be trilateral, quadrilat ...

al shape, emerging some 10 metres from the ground level and with a circumference of about 50 metres. Its

elevation The elevation of a geographic location is its height above or below a fixed reference point, most commonly a reference geoid, a mathematical model of the Earth's sea level as an equipotential gravitational surface (see Geodetic datum § Vert ...

is 368 MSL. It stands in a woody and almost plain spot close to the border between

and

Alpignano Alpignano (; pms, Alpignan ) is a ''comune'' (municipality) in the Metropolitan City of Turin in the Italian region Piedmont, located about west of Turin on the Dora Riparia in the Val di Susa plain. Twin towns – sister cities Alpignano is t ...

, not faraway from the small Lake of Caselette. The place is still of a good environmental quality, although almost encircled by industrial and residential areas.

Geology

The Pietra Alta belongs to the ''Morainic amphitheater of Rivoli-Avigliana'', and in particular to the

moraine A moraine is any accumulation of unconsolidated debris (regolith and rock), sometimes referred to as glacial till, that occurs in both currently and formerly glaciated regions, and that has been previously carried along by a glacier or ice shee ...

left by the

Riss glaciation The Riss glaciation, Riss Glaciation, Riss ice age, Riss Ice Age, Riss glacial or Riss Glacial (german: Riß-Kaltzeit, ', ' or (obsolete) ') is the second youngest glaciation of the Pleistocene epoch in the traditional, quadripartite glacial classi ...

. It was transported to its present location by the hudge glacier which occupied the

Susa Valley The Susa Valley ( it, Val di Susa; pms, Valsusa; french: Val de Suse; oc, Val d'Ors) is a valley in the Metropolitan City of Turin, Piedmont region of northern Italy, located between the Graian Alps in the north and the Cottian Alps in the sou ...

. Its height on the ground level, remarkable if compared to other glacial erratics of

Piedmont it, Piemontese , population_note = , population_blank1_title = , population_blank1 = , demographics_type1 = , demographics1_footnotes = , demographics1_title1 = , demographics1_info1 = , demographics1_title2 ...

, can be explained because the Pietra Alta, unlikely other boulders mostly covered by the ground, is almost fully exposed. It consists in a huge block of

serpentinite Serpentinite is a rock composed predominantly of one or more serpentine group minerals, the name originating from the similarity of the texture of the rock to that of the skin of a snake. Serpentinite has been called ''serpentine'' or ''ser ...

with a

volume Volume is a measure of occupied three-dimensional space. It is often quantified numerically using SI derived units (such as the cubic metre and litre) or by various imperial or US customary units (such as the gallon, quart, cubic inch). The de ...

of 2.600

cubic metres The cubic metre (in Commonwealth English and international spelling as used by the International Bureau of Weights and Measures) or cubic meter (in American English) is the unit of volume in the International System of Units (SI). Its symbol is ...

. On its surface can be detected rinds similar to the so-called ''

desert varnish Desert varnish or rock varnish is an orange-yellow to black coating found on exposed rock surfaces in arid environments. Desert varnish is approximately one micrometer thick and exhibits nanometer-scale layering. Rock rust and desert patina are ot ...

es'', considered by geologist an indicator of a

semi-arid climate A semi-arid climate, semi-desert climate, or steppe climate is a dry climate sub-type. It is located on regions that receive precipitation below potential evapotranspiration, but not as low as a desert climate. There are different kinds of semi-ar ...

Uses

On the boulder there are a lot of

climbing Climbing is the activity of using one's hands, feet, or any other part of the body to ascend a steep topographical object that can range from the world's tallest mountains (e.g. the eight thousanders), to small boulders. Climbing is done fo ...

routes, and its sides are equipped with bolts and

piton A piton (; also called ''pin'' or ''peg'') in climbing is a metal spike (usually steel) that is driven into a crack or seam in the climbing surface using a climbing hammer, and which acts as an anchor for protecting the climber against the ...

s in order to protect the climbers. Many of these routes, some of them very engaging, were described at the beginning of the

1980s File:1980s replacement montage02.PNG, 420px, From left, clockwise: The first Space Shuttle, ''Columbia'', lifts off in 1981; US president Ronald Reagan and Soviet leader Mikhail Gorbachev ease tensions between the two superpowers, leading to the ...

by the alpinist Gian Carlo Grassi in his book '' Sassismo spazio per la fantasia: arrampicate sui massi erratici della Valle di Susa''. The environment surrounding the Pietra Alta is considered very suggestive; the boulder can be easily reached on foot from Caselette following ''Via Pietra Alta'', a small asphalted lane which continues with a pedestrian dirt road.

References

{{Commons category, Pietra Alta (glacial erratic) Landforms of Piedmont Glacial erratics of Italy Rock formations of Italy Climbing areas of Italy