Topographically, Japan is a rugged land of high mountains and deep valleys, with many small plains. Because of the alternating sequence of mountain and valley, and the rocky soil, only an estimated 11% of Japan is arable land. Plains and mountains. The Japanese plains lie chiefly along the lower courses of the principal rivers, on plateaus along the lowest slopes of mountain ranges, and on lowlands along the seacoast. The most extensive plains are in Hokkaido: along the Ishikari R. in the W part of the island, along the Tokachi R. in the SE, and around the cities of Nemuro and Kushiro on the E central shore. Honshu has several large plains. That of Osaka contains the cities of Kobe, Kyoto, and Osaka; the plain of Kanto is the site of Tokyo; and Nagoya is the location of the plain of Nobi. The plain of Tsukushi is the most important level area in Kyushu. The mountains of Japan are the most conspicuous feature of the topography. Mountain ranges extend across the islands from N to S, the main chains sending off smaller ranges that branch out laterally or run parallel to the parent range, and frequently descend to the coast, where they form bays and harbors. In the N, the island of Hokkaido is marked by a volcanic range that descends from the Kurils and merges in the SW part of the island with a chain branching from Point Soya in the NW tip. These mountains branch into two lines near Uchiura Bay, on the SW coast, and reappear on the island of Honshu in two parallel ranges. The minor range, situated entirely in the NE, separates the valley of the Kitakami R. from the Pacific Ocean. The main range continues toward the SW until it meets a mass of intersecting ridges that enclose the plateau of the Shinano R. and forms a belt of mountains, the highest in Japan, across the widest part of the island. The highest peak, at 3776 m (12,389ft), is Fuji, an extinct volcano near Yokohama, which, because of its exceptional beauty, is one of the favorite themes of Japanese art. One of the subsidiary chains in the central mountain mass is called the Japanese Alps because of the grandeur of the landscape; the highest elevation in the chain is Mt. Yariga (3180 m/10,433 ft). Farther S is another chain of high peaks of which Mt. Shirane (3192 m/10,472 ft) is the highest. The islands of Shikoku and Kyushu are dotted with mountain ranges, although none contains any peak higher than Ishizuchi (1981 m/6499 ft) on the island of Shikoku. Volcanoes are common in the Japanese mountains; some 200 volcanoes are known, about 50 of which are still active. Thermal springs and volcanic areas emitting gases are exceedingly numerous. Rivers and Lakes. Although Japan is abundantly watered—almost every valley has a stream—no long navigable rivers exist. The larger Japanese rivers vary in size from swollen freshets during the spring thaw or the summer rainy season to small streams during dry weather. Successions of rapids and shallows are so common that only boats with extremely shallow draft can navigate. The longest river in Japan is the Shinano, on Honshu, which is about 370 km (about 230 mi) long; other large rivers on Honshu are the Tone, Kitakami, Tenryu, and Mogami. The important rivers of Hokkaido include the second largest river of Japan, the Ishikari, and the Teshio and Tokachi. The Yoshino is the longest river in Shikoku. Japan’s many lakes are noted for their scenic beauty. Some are located in the river valleys, but most are mountain lakes and many are summer resorts. The largest lake is Biwa, on Honshu, which covers about 672 sq km (about 259 sq mi).