Fossa Magna is a major Rift Valley or tectonic depression in central Japan. It marks the boundary where the southwest and northeast arcs of the Japanese archipelago meet. It is a region of intense geological activity, characterized by a series of faults and many of Japan’s most famous volcanoes. ANSWER: (B) Rift valley
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The term literally means “Great Ditch.” This tectonic feature formed during the opening of the Sea of Japan. The Fossa Magna contains the Itoigawa-Shizuoka Tectonic Line and is filled with thick layers of volcanic and sedimentary rocks. This rift divides the Japanese landmass geologically and biologically. Because it is a zone of crustal weakness, many volcanoes, including Mount Fuji, have formed within or along its margins. It is a primary area of study for understanding the complex plate tectonics of the Japanese island arc.