The Apennines or Apennine Mountains ( ; ) It is now known to be not an erosional feature, but is a filled portion of the Adriatic Trench, called the Adriatic foredeep after its function as a subduction zone was discovered.

Apennine orogeny

thumb|A [[pillow lava from an ophiolite sequence, Northern Apennines]]

The Apennine orogeny is a type of mountain-building in which two simpler types are combined in an apparently paradoxical configuration. Sometimes this is referred to as "syn-orogenic extension", but the term implies that the two processes occur simultaneously during time. Some scientists imagine that this is relatively rare but not unique in mountain building, whereas others imagine that this is fairly common in all mountain belts.

The RETREAT Project have this specific feature as one of their focus points

In essence the east side of Italy features a fold and thrust belt raised by compressional forces acting under the Adriatic Sea. This side has been called the "Apennine-Adriatic Compressional Zone" or the "Apennines Convergence Zone." On the west side of Italy fault-block mountains prevail, created by a spreading or extension of the crust under the Tyrrhenian Sea. This side is called the "Tyrrhenian Extensional Zone." The mountains of Italy are of paradoxical provenience, having to derive from both compression and extension:

<blockquote>"The paradox of how contraction and extension can occur simultaneously in convergent mountain belts remains a fundamental and largely unresolved problem in continental dynamics."</blockquote>Both the folded and the fault-block systems include parallel mountain chains. In the folded system anticlines erode into the highest and longest massifs of the Apennines.

According to the older theories (originating from the 1930s to 1970s) of Dutch geologists, including Van Bemmelen, compression and extension can and should occur simultaneously at different depths in a mountain belt. In these theories, these different levels are called Stockwerke. More recent work in geotectonics and geodynamics of the same school of geoscientists (Utrecht and Amsterdam University) by Vlaar, Wortel, and Cloetingh, and their disciples, extended these concepts even further into a temporal realm. They demonstrated that internal and external forces acting upon the mountain belt (e.g., slab pull and intra-plate stress field modulations due to large scale reorganisations of the tectonic plates) result in both longer episodes and shorter phases of general extension and compression acting both upon and inside mountain belts and tectonic arches (See e.g. for extensive reviews, bibliography and discussions on the literature:

Van Dijk (1992),

Van Dijk and Okkes (1991),

Van Dijk & Scheepers (1995),

and Van Dijk et al. (2000a)

The strike of the Apennine subduction zone forms a long, irregular arc with centers of curvature in the Tyrrhenian Sea following the hanging wall over which the mountains have been raised; i.e., the eastern wall of the mountains. It runs from near the base of the Ligurian Apennines in the Po Valley along the margin of the mountains to the Adriatic, along the coastal deeps of the Adriatic shore, strikes inland at Monte Gargano cutting off Apulia, out to sea again through the Gulf of Taranto, widely around the rest of Italy and Sicily and across inland north Africa. The most unstable terrain in the Apennines when the landslide sites are plotted on the map are in order from most unstable the eastern flanks of the Tuscan–Emilian Apennines, the Central Apennines and the eastern flank of the southern Apennines. Instability there is comparable to the Alps bordering the Po Valley. The most stable terrain is on the western side: Liguria, Tuscany, Umbria and Lazio. The Apennines are slumping away to the northeast into the Po Valley and the Adriatic foredeep; that is, the zone where the Adriatic floor is being subducted under Italy. Slides with large translational or rotational surface movements are most common; e.g., a whole slope slumps into its valley, placing the population there at risk.

Glacial ice

Glaciers no longer exist in the Apennines outside the Gran Sasso d'Italia massif. However, post-Pliocene moraines have been observed in Basilicata.

Major peaks

The Apennines include about 21 peaks over , the approximate tree line (counting only the top peak in each massif). Most of these peaks are located in the Central Apennines.

Bibliography

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