The general aspect of a landscape is  strictly linked to the course and the disposition of   rocky formations: only starting from their knowledge we can read and  understand a territory and therefore protecting  it and managing it the right way. The active geomorphologic agents are those that actually modify rocks and the rocks constitute the starting point of a landscape evolution. The geomorphologic agents  process a physical alteration (frost and sudden temperature changes), and so do running waters (rains, brooks, streams, rivers...), the wind, and living beings (above all the vegetation).
Along with geomorphologic agents, one cannot forget mankind, who can limit, but often also  increase the erosion phenomena  and modelling reliefs.The frequent and characteristic terracings visible along the valley are a positive example of man’s work; less positive are the badly performed interventions that has increased  the fragility of habitats and  favoured hydrogeological instability and environment deterioration. Especially certain roads laid down without particular criteria, wrong reforestations and forest fires. Any of the geomorphologic agents can prevail on the others, giving to landscape particular features, but, concerning chemical and physical alterations of the rocks, watercourses regime with light or heavy rain, warm or cold temperatures, and weather conditions, climate is important too.
Therefore the modelling factors of a landscape are numerous and mutable and they almost always act together in different ways and at  different times: from the few instants of a landslide up to ten millions of years during which a mountainous chain rises.
The following are the main kinds of  landscape in Trebbia Valley .The  erosion which model the terrestrial surface, due to atmospheric agents is easily observed in case of diversified erosion, typical in sedimentary rocks of the zone; during  the sedimentary deposition of materials, different type of layers form: on the Mount Antola there are alternatively the sedimentation of limestone, clay, or sandy material.Rocks behaviour changes according to the erosion operated by watercourses: sandstone, more resistant, tends to remain in a higher position than shale which is tender and easily erodibile.
These phenomena are visible in Bric Rondanina, Costa, above Pentema...Besides rocks, grounds are affected by superficial erosion. If vegetation does not protect the ground sufficiently from heavy rain, the erosion process speeds up enormously, starting a sort of accelerated erosion: in such case the ground gets removed faster than it can form itself.
After heavy rain, on poor vegetation grounds, one can observe numerous gullies engraving the ground with long and parallel lines, and subsequently ending up into a brook: this phenomenon is known as "brookment." Landslides and slumped grounds are  local geomorphologics phenomena: in a mainly mountainous territory as Liguria is, and particularly in the Trebbia Valley, landslides and slumped grounds are a constant danger,  ending up being a determining parameter in laying down roads and building houses.
While slumped grounds are frequent everywhere especially where  slopes are steep, landslides has occurred in  Luvega, Moglioni and Bric Rondanina. The erosion due to watercourses or torrential erosion, led to the localization of an idrographic network. On the Trebbia Valley map one can detect the main watercourse (Trebbia River) and numerous  secondary watercourses that kind of get into it perpendicularly.
The Trebbia river, in the upper part of the valley flows among steep walls, almost vertical, between ravines and gorges by suggestive beauty. Its small tributaries go down quickly on the rocky bed of little steep valleys: they are rich of water in autumn and at the end of winter, and almost dry after a summer subject to drought. These tributaries hollow the rock out  deeply, according to water speed and to the nature of the rock.
The watercourses erosion not only acts in depth, but also on the river edges. The side erosion becomes evident when water current  sways; from the opposite side, the weaker current tends to deposit sediments, causing floods:  according to the current and to the vegetation, pebbles of different nature along the Trebbia river, assume different forms:  lens-shaped or semi-lunar shaped.
On the rocky bed of some watercourses (such as the Terenzone River and the Pescia River) one can observe characteristic forms of erosion, represented by kind of circular hollow by different depth and different diameter.
On the bottom of these basins, so-called pothole, one can often find round pebbles, which contribute to model the round form of the basins through the circular movement generated by water current. Perhaps the most important forms of torrential erosion, at least under the landscape profile, are the meanders. Meanders  form when the river flows slowly into the plain with little inclination ; if the level of the sea lowers, watercourse takes again speed, and it starts digging again, following the course of the ancient bed by sinuous forms. Through this process, the so-called "boxed meander" can form among steep walls of rock,  such as the ones in Trebbie Burche , in Emilian territory, just right before the confluence with the Aveto River.
A phenomenon of watercourse capture or picking up is visible near Laccio. For a  better understanding one needs to know that direct erosion proceeds digging backwards: in the case of two drainage basins separated by a thin ridge of watershed, the stream by the biggest erosive action succeeds in "capturing" the highest part of the other stream. In this case the Scrivia stream has captured the Laccio stream, which is the highest part of the Bisagno stream. As a matter of fact  the Laccio stream brusquely folds up westwards, towards Montoggio Village, becoming the Scrivia stream. In the calcareous zones the dolinas are present wich are  depressions of the ground  basins not wet by water, neither completely nor partially. They generally form  from cave ceiling collapse and its following filling up. Dolinas form and dimensions may vary; on the bottom, water is stagnant and favours typical vegetation of damp zones. A good example of dolina is the one in “Pian della Cavalla” (horse’s plain). In Liguria evident phenomena caused by glaciations do not exist: therefore neither glacial valleys nor lakes of glacial origin (except the ones in Agoraie, Aveto Valley) are to be found .
In Trebbia valley, geomorphologic observations referred the glaciations concern only Roccabruna Mountain slopes, where a peat bog can offer you interesting cues around the reconstruction of the climatic events in our region.

(Article based on the publication "naturalistic Itineraries" by Comunità Montana Alta Val Trebbia – High Mountainous Trebbia Valley Community )