Geomorphology
Apuan Alps landforms and deposits
 

Relief landforms

The Apuan Alps are characterized by a physical landscape with Alpine features or perhaps features more similar to those of the Lombard Prealps, if the famous comparison by Antonio Stoppani in “Il bel paese” (The beautiful Country) (1876) is to be recalled. The geologist compared the fields of the Po Plain to the Ligurian Sea because of their being flat at the foot of the mountains. The range’s sharp and therefore “Alpine” morphology is more evident on the coastal side. The inland side has similar characteristics but its profile is slightly more gentle.

As a matter of fact, there is “asymmetry” on the main two sides of the range because of different levels of steepness and the overall direction of the mountain range owing to structural more than morphogenetic reasons.
Since the Middle-Late Pliocene onwards, the differences between the two sides of the Apuan Alps have greatly increased as the denudation process, depending on tectonic rather than erosional elements, developed within complex uplift and quiet stages of the Apuan range. The axis of the range was oriented by the deformation geometry which was also responsible for the position of carbonate formations along the main alignment of the range itself.
 

Therefore, the coastal side was characterized by an early exposure of marble and metadolomites as well as a rapid and intense erosion of the valleys not least because of the occurrence of Paleozoic Phyllites in the west, now denudated and therefore more easily erodible.
On the other hand, on the inland side the evolution of the physical landscape was characterized by a long period during which the Tuscan Nappe covered the ‘Metamorphic Complex’. The limbs of the folds with “apenninic” vergence have accompanied the slope toward the Serchio graben more gently.
Apuan transverse valleys, with “Adriatic flow”, were antecedent to the late upthrust of the horst of the tectonic rift itself. The particular distribution of plastic and rigid structural elements, on which played mainly the fluvial morphogenetic action, has contributed to the “asymmetry” between the two main sides of the Apuan Alps.
On the coastal side, the Apuan Alps create a vertical barrier with narrow and deep valleys, whereas on the inland side slopes descend, more regularly and more similarly to the Northern Apennines’ morphology.
Yet, the range never lowers in a uniformed fashion as the slope is regularly interrupted by terrains with low inclination. Moreover, the inclination angle is different but constant on the two main sides. Orographic anomalies are concentrated within certain altitudes (500-650; 750-850; 900-1,050; 1,200-1,250; 1,500-1,600 m) and bear the marks of past morphological features.

"Alpine" morphology of the Apuan mountains
 

Supposedly, they are orographic terraces which were ancient basal levels during phases of tectonic quiet, then re-carved by superficial running water during uplift phases.
The heritage of a relatively mature morphology is still visible in some embedded meanders which are scattered along the narrow Apuan thalwegs. In fact, these meanders have superposed on higher and wider valleys, cutting the bedrock, during a phase of relif-rejuvenating. 
The layout of the hydrographic network in the Apuan Alps has been affected by differences in the structural setting and the morphological “asymmetry” of the main mountain sides. On the coastal side, where slopes are steeper, valleys are radially arranged and join together at lower altitudes. On the inland side, which is less steep, each watercourse keeps its initial direction, perpendicular to the main ridge. Parallel valleys prevail on the eastern side, whereas the western side is characterized by more or less complex systems of converging valleys with dendritic or subdendritic hydrographic networks. Apuan watercourses belong to three different categories, depending on whether they flow into the Ligurian Sea or they are tributaries of the Rivers Serchio or Magra. The western side is characterized by rivers with steep upper courses reaching the sea after crossing the short coastal plain largely originated by their deposits.
 

Zucchi di Cardeto: cuèstas landscape
 

The whole coastal surface, amounting to 315 km², is divided into hydrographic basins of different dimensions, of which that of River Versilia accounts for 1/3 and is twice as large as the surface covered by the Carriona and Frigido watercourses.
Most of the inland side of the range, amounting to 545 km², belongs to the hydrographic basin of the River Serchio as parallel valleys are crossed by its right tributaries.
All tributaries have a length comprised between 9 and 14 km. The longest is Serchio di Minucciano, followed in order by Tùrrite Secca, Tùrrite di Gallicano, Èdron and Tùrrite Cava.
In the northern area of the inland side, totalling almost 220 km², watercourses, starting from streams Lucido and Bàrdine descending from the Apuan mountains, join River Magra through the stream Aulella.

The presence of highly permeable carbonate rocks across the main ridge contributes to the existence of intermittent watercourses with semi-permanent or temporary regimes, especially in their upper courses. A well-know case is the karst circulation of River Tùrrite Secca, which is characterized by a 4 km-long underflow when flowing along the Mt. Sumbra southern side

 

Karst landforms and deposits

Despite heavy rains, the central part of the main range is arid and bare on the surface, as rainwater is immediately absorbed by the carbonate bedrock and released in large, complex hypogean karst Systems. Water flows down into the mountains and, upon reaching the impermeable Paleozoic basement, it emerges from karst springs located between 200 and 500 m of altitude. The phenomenon is evident on the coastal side and it is often the reason for the extension of the hydrogeological basin, larger than their hydrographic basin. Water is captured from the eastern to the western side of the ridge through underground paths in karst aquifers. This creates larger catchment areas for Rivers Frigido, Versilia and Carriona compared to those created on the surface by the watersheds.
Despite large areas of carbonate rocks outcrop, the epigean karst forms in the Apuan Alps are not well developed in medium and large scale. In these formations harsh and steep orographic features contributed to other morphogenetic processes, which is why epigean phenomena are mainly represented by small karst landforms. They are particularly common on pure calcareous rocks (Marble and “massiccio” Limestone) characterized by intense fracturation, high infiltration and scarce vegetation cover.
 

Hell's Valley (Mt. Pania): epigean karst landforms
 

The most common microforms, the karren, are solution pits, grooves and runnels. Karren fields are widespread at high altitudes, where the snow is more persistent and rocks are more fractured forming a karst landscape with clints and grikes. Dolines and shallow wells are less frequent and amount to 180 units in the whole mountain range.
They are morphoscultpures of various dimensions, from metres to decametres long, often quite deep and therefore with a bowl or funnel-like shape or even snow dolines.
Dolines are usually either isolated or gathered in small groups (Campocecina, Spallone, Pian della Fioba, Passo Sella, Vetricia, etc.) in areas with little inclination and facing north-eastern quadrants.
The north-eastern side of Mt.Tambura in Carcaia and, to a lesser extent, the northern side of Mt. Pisanino are characterized by an unusual karst landscape with numerous concave dissolution forms.

Epigean forms have seen a reduced development, whereas hypogean karst phenomena in the Apuan Alps acquire paramount importance and extreme value. The Apuan Alps boast 19 out of the 50 deepest caves and 8 out of the 50 longest karst cavities in Italy. The Geopark is also home to Italian all-time records: Abisso Paolo Roversi (Paolo Roversi Abyss), the cave with the largest difference in heights (1358 m) and Antro del Corchia, the longest karst Complex (~ 60 km).
 

So far speleological research has found more than a thousand karst caves formed by gravitative hypogean circulation, both in vadose and phreatic conditions, from high-altitude infiltration areas to low-altitude emergence areas. The Apuan caves are mainly characterized by wells, sometimes in a sequence, which have developed in the vertical transfer zone of infiltration water. They were originated from small superficial absorption fractures which then expanded and deepened by corrosion until they reached huge differences in heights, sometimes exceeding a kilometre. Caves originated by horizontal water transfer are less frequent but not unusual. They are characterized by sub-horizontal tunnels and labyrinths on gentle slopes originated near the saturated zone during phases of tectonic quiet of the Apuan Alps. There are tipically phreatic morphologies (pressure conduits) or morphologies conducting rainwater (canyons).
Karst Complexes with a spatial mix of wells and tunnels as a result of polyphasic evolution are rarer. They derive from the superposition of different generations of caves with horizontal features associated to phases of tectonic inactivity and vertical features which formed after the relief-rejuvenations. The largest cavities of the Apuan Alps belong to this special category and Antro del Corchia is its main example. As a matter of fact, the Apuan Alps still preserve traces of “ancient” karst phenomena, probably dating back to the first phases of denudation/erosion of carbonate rocks of the “Metamorphic Complex”. Witness the numerous “relict” tunnels along the higher ridges of the mountain chain, which are characterized by cavities with large section and reduced linear development. Therefore, they are truncated segments of once larger karst Systems formed by the progressive erosion of mountain sides and the general deepening of the valleys.

Wind Cave (Mt. Pania): pendant room
 

Glacial landforms and deposits

In the Apuan Alps, the Quaternary Glaciation left clear and remarkable traces of diffuse erosion and deposit landforms despite the moderate height of mountain peaks and their vicinity to the sea. The mountain range provides an obstacle to Atlantic humid currents and nowadays causes heavy orographic rain. It is likely that during cold phases in the Pleistocene it was responsible for heavy solid precipitation leading to the formation of perpetual snowfields. The glacial phenomenon mainly developed on the inland side of the mountain range, yet recognizable and remarkable traces are also found on the coastal side. Since glaciers were exposed to the north-east and located on a more gentle slope, they could build up more and survive longer, compared to the opposite side which was hampered by the relief-energy and its exposure to southern quadrants.
 

The Apuan Glaciers during the Wurm Maximum (reconstruction)
 

Attempts to piece together the glacial extension of the Apuan Alps led to the identification of twelve large valley glaciers on the inland side of the range. The main glacier (Orto di Donna-Val Serenaia-La Mandria) is likely to have extended over more than 12 km² with a length of 6 km. The side exposed to the sea saw the formation of few perpetual snowfields in the shape of cirque, slope, niche, mountain, valley glaciers. The terminal part of the tongue of the Pizzo d’Uccello glacier reached Solco d’Equi Terme at a lower altitude of 475 m a.s.l. Whereas, the ice tongue of Arnetola basin, along Edron valley, is thought to have descended to 550 m a.s.l. The formation of terminal moraines at a low altitude shows the exceptional nature of the glaciation in the Apuan Alps. As a matter of fact, it is different from what happened in the whole Apennines and the western Alps at similar altitudes.
Apuan glaciers descended to very low altitudes and this was accompanied by the exceptional low level of the snow line.

More recent calculation methods estimate that the ideal line of balance between the accumulation and fusion of snow was to be found at around 1250-1300 m a.s.l., at least on the northern side of the range.
The formation of glaciers in the Apuan Alps is unanimously linked to the Würm on the basis of deductive reasoning, even though a Pre-Würm (Riss?) glaciation has been also suggested by the occurrence of cemented glacial deposits covered by more recent melted moraine deposits (Passo del Vestito, Val Terreno, Solco d’Equi). The glacial growth kinematics is unknown, whereas the retreat was quick and not uniform, considering the small number of documented late glacial phases.
The Apuan glaciation has preserved the main erosion forms. The glacial cirque is the most widespread morphosculpture in the whole range but it is rarely found in its typical form with semicircular vertical cliffs, a flat bottom and a reverse slope threshold (Grotta Giuncona, Cervaiole and Catino del Sagro are among the best preserved). A number of crests (Mt. Sumbra, Corchia and the south-east side of Mt. Altissimo) are characterized by close or coalescent small cirques perfectly carved on southward-looking carbonate walls. Saddles, which lower Apuan crests, especially along the main watershed, enabled glaciers to cross mountain sides.
 

Transfluence saddles are more common (Foce Giovo, Focolaccia, Passo Sella, Foce di Mosceta), whereas diffluence saddles are rarer (Foce Pianza, Passo del Vestito).
The inland side (Pianizza, Fatonero, Orto di Donna) houses typical U-shaped glacial valleys with a parabolic cross-section and overdeepened glacial basins which have often been characterized by peat bogs and wetlands (Mosceta, Fociomboli, Campocatino, Pianellaccio, etc.). Valley steps, perhaps linked to a stop of the glacier retreat are more often found in the furthest northern area of the Apuan Alps (Orto di Donna, Acqua Bianca, Pisanino), whereas “Marmitte dei Giganti” (Giant’s pot-holes) along the ditches Fatonero and Angullaja (southern side of Mt. Fiocca and Mt. Sumbra) are likely to have a fluvioglacial origin. Finally, roches moutonnées are not widespread. The only few examples can be found in Val Serenaia and Arnetola.
Depositional landforms predominantly comprise glacial ridges mainly showing terminal moraines and to a lesser extent lateral and stadial moraines. Terminal arches are well recognizable in various inland Apuan valleys (i.e. Canale del Libardo in Gramolazzo), whereas Campocatino depression boasts the best preserved morainic amphitheatre characterized by concentric circles of ridges. Huge glacial erratics are found in the valleys of Rivers Edron and Serchio di Gramolazzo. In particular, marble erratics have been subject to quarrying activity in Vagli di Sopra and Campocatino.
As it is well known, nowadays there are no active glaciers in the Apuan Alps. Perpetual snowfields have been preserved at the bottom of high-altitude karst wells (“snow holes”), especially in the group of Pania della Croce, even at a few metres depth. On the surface there are places maintaining their snow cover until the hot season and even late summer. A case in point is the place at the bottom of the northern wall of Mt Pizzo d’Uccello which is indicated with the name “Corners of old snow” on the maps of the Italian Military Geographical Institute (IGMI).

Vinca: glacial morphology
 

from right to left: Cresta Botto; Punta Carina, Punta Graziosa, Sicilia, Ferro; Coda del Cavallo