The Japanese territory includes over 3000 islands, small and large, which from Sahalin and the Kuril Islands (of which Japan claims the southern section to the former USSR) through the Ryūkyū lead to Taiwan (Formosa). However, most of its surface (61%) falls on the island of Honshū or Hondo (231,090 km²), the heart of Japanese civilization and home to the main hubs of its geographical organization. The other major islands are Hokkaidō (78,523 km²), Kyūshū (42,163 km²) and Shikoku (18,783 km²). The birth of the archipelago is connected to the tectonic perturbations typical of the marginal areas of the continents and, more generally, to the great circle of instability that surrounds the Pacific Ocean. Already in the Paleozoic era there was a geosyncline subject to incessant evolutionary processes in the area now occupied by the archipelago. Towards the end of that era there were the first orogenetic manifestations (Akiyoshi orogeny) coeval with the European Hercynian ones. They led to the emergence of the first reliefs, whose alignments are found in the innermost part of Honshū. At the end of the Mesozoic, a new (Sakawa) orogeny, parallel to the Alpine one, determined further upheavals. Visit justinshoes.net for Asia geography.
Cenozoic, a time when much of the Japanese territory had emerged from the sea. In the second half of the Cenozoic, however, there were new convulsions: thus the current mountain arches were outlined, the depressions that today constitute the seas of Okhotsk and Japan were formed and the volcanism that built new reliefs above, or on the margins, of the old ones came to life. structures. The settlement of the Japanese area is still in progress and its instability is made critical by the existence of the deep ocean trenches that delimit the archipelago on the Pacific side and which in several points exceed 10,000 m in depth (Kuril pit, -10.542 m; Japan trench, -10.680 m). The structural instability of the Japanese area – one of the most disturbed in the so-called “fire belt” of the Pacific – is concretely revealed by the frequency of seismic events and the intensity of volcanic activity, which deserves the fame of the archipelago. of “forge of volcanoes”. Structurally, the archipelago consists of several mountainous arches knotted together. The main ones are those of northern Honshū and Shikoku (or southern Honshū); they connect with the Bonin-Volcano arch (placed in an almost normal direction) in the central section of Honshū, in correspondence with the so-called Fossa Magna, a sinking area, formed by some large faults, which divides the largest Japanese island into two parts. The other arches are to the S that of the Ryūkyū, which on the island of Kyūshū is knotted to that of Shikoku, and to the N the arches of the Kurils and of Sahalin, which in Hokkaidō connect with that of the northern Honshū. In the island sections thus defined, the geological formations vary somewhat; in general we recognize an internal zone facing the Asian continent and an external one facing the Pacific Ocean. This geological and structural division is particularly clear in the Shikoku arc, being given by a longitudinal fracture that separates the internal part, dominated by massive granite rocks, from the external one, where strongly corrugated schist and sedimentary rocks prevail. This division is less clear in the northern section of Honshū, where intrusive granite formations occur almost everywhere; the schistose and sedimentary rocks appear instead in the internal section of the Hokkaidō, linking to the Sahalin ridge. Overall, however, there is a great variety of geological formations in Japan even in rather restricted areas, a phenomenon due to the intensity and complexity of orogenetic convulsions. On all the basic formations, granite or metamorphic, the recent volcanic ones overlap, which in the northern Honshū and in the Hokkaidō correspond to the median mountain ridges, while in the southern section of the Honshū and in the Shikoku they give rise to a more fragmented relief. The importance of volcanic formations in Japan is revealed by a simple fact: they affect 26% of the entire archipelago. Volcanic activity, connected to the Cenozoic disturbances, it has also been intense in recent times and as many as 60 volcanoes have had eruptions in historical times. Today the active volcanoes are not numerous; they are completely lacking in southeastern Honshū and Shikoku, while they are numerous in Kyūshū, northern Honshū and Hokkaidō. Some represent the summits of the mountainous areas to which they belong and a volcano is still the highest peak of the entire archipelago, the Fuji (3776 m), mountain-symbol of the Japanese landscape, built near the Fossa Magna; the suggestive cone rivals the peaks of the Japanese Alps, the highest section of the internal ranges, reaching 3192 m in the Shirane. These reliefs are the rejuvenation of the Paleozoic chains and have youthful forms; this also applies to the other Japanese mountain systems, all more or less subject to the great Cenozoic rejuvenation. Overall, the morphology is sweeter in the areas dominated by volcanic formations, characterized by very elastic lava expansions that have smoothed the roughness of the slopes.
Most of the Japanese territory is in any case mountainous (it is estimated that 75% consists of hills or mountains) and, apart from the section of Honshū dominated by the Japanese Alps and Fuji, all the island watershed ridges touch the 1500-2000 m high. L’ The course of the valleys is complex and in general a transverse course near the coasts is followed by longitudinal furrows aligned in the direction of the structural chains, from NE to SW. Flowing on the coasts, these valleys give rise to the few plains available to Japan, formed by alluvial contributions that have led to the filling of coastal outlets. A case in itself is represented by the plain of Kantō, the largest in the country, formed at the Fossa Magna by sedimentation of recent materials, in particular volcanic ones (loam) that make this region very fertile, the immediate hinterland of Tōkyō (of which it can explain the exceptional development). Another extensive plain is that of Tokachi, in Hokkaidō; the island also has the wide plain of Sapporo. The coasts of the Japanese archipelago (a total of 26,813 km) are extremely rugged and varied. In their current profiles they are the result of the most recent upheavals that have led to the emergence of new surfaces of already complex and tormented areas orographically. The Pacific side has the roughest and most articulated outline, while the coasts of the Sea of Japan are overall more linear, with long stretches of low and sandy coastline; the peninsula of Noto is an exception (island of Honshū), a long prominence consisting of a tongue of land welded with old island formations. Along the Pacific the dominant motif is offered by the deep and articulated inlets (wan) and by the wide bays (umi), overlooked by the large port centers that are at the origin of Japan’s commercial fortunes; stand out, all in Honshū, Tōkyō-wan, with the ports of Tōkyō and Yokohama; Ise-wan, which is home to Nagoya; Ōsaka-wan, seat of the Ōsaka- Kobe port complex; and, in Kyushu, Kagoshima-wan and Ariake-kai. A particular element of the Japanese coastal contour is the maritime space (Seto naikai or Inland Sea) that separates the Shikoku from the southwestern Honshū, a sea scattered with islands and islets derived from the emergence of the reliefs between the mountain ridges that dominate the two islands; the insular fragmentation here follows that of the coast, sometimes broken by inlets to rías. There are few low coasts on the Pacific side: they correspond to the stretches of the most extensive plains (especially in the Hokkaidō, in addition to that of the Kantō) and to the sickles or delta expansions at the outlets of the valley bottoms.