Considerazioni preliminari sulla morfologia e sul reticolo idrografico dell'Appennino settentrionale tra i Torrenti Orba (Prov. di Alessandria) e Nure (Prov. di Piacenza)

Abstract

This paper describes the morpho-iogical and hydrographic features of the area delimited by the Orba river to the W, the Tyrrhenian-Adriatic watershed to the S, the Nure river to the E and the margin of the Po River Plain to the N. Many pieces of physiographic evidence are discussed; in particular, if only the highest elevations in the area are considered, the continuation of the Northern Apennines ridge axis up to the Ebro-Antola "plate" can be identified as well as the meridian alignment cutting it. The two alignments govern the hydrography and direction changes of the numerous streams of the area. The great discrepancy between the ridge axis and the recent Apennines divide, which is lowered and shifted southward, is highlighted. By enveloping the highest ridges in the area with an ideal surface it can be seen that the Genoa me-ridian separates two very different landscapes: A narrow and low landscape to the west and a wide and highly-elevated one to the east. The axes of these two areas trend in different directions with the former oriented approximately NE and the latter approximately NW.