Complex and Brittle Geological Features Caused by Uplift, Great Fault, and Volcanic Activities
The Hida mountain range commonly known as the “North Alps” with the tall and sharp rocks, crests, and snow patches stretching all the way deserves exactly the name of the “Alps” given to it in appearance. From the geological viewpoint, the granite and the porphyrite that are the igneous rocks penetrate the sedimentary rock that was created during the palaeozonic era, which is in part covered with the ejecta from a volcano. The beautiful ridges were made by gradual weathering of a group of its isolated mountains through the action of volcanic activities added after the fierce uplifting movements during the palaeozonic era and the mountain-making movements of the great fault. The North Alps is still undergoing an uplift although it is not noticeable. In the meanwhile, the brittle soil such as the weathered sedimentary rock and metamorphic rock is collapsed into earth and sand, and continues to be transported downstream. Besides, Yakedake that is the only active volcano in the North Alps grows through the volcanic activities, and is, so to speak, a mountain made through the accumulation of lava flow, pyroclastic flow, and debris flow. Therefore, you have to be on alert for the brittle and collapsible ground at all times.
Fossa Magna and Itoigawa-Shizuoka Tectonic Line Fossa Magna refers to the “Great Crevasse” in Latin. Its godfather was Dr. E.Nauman, a German geologist who was offered a position by the Meiji government. About 30 million years ago, energy erupted from under the Asian continent, and lava started to overflow the continent, while the origin of the present Japanese Islands started to become separated from the continent. It appears that the southern Japan was split into a lump, while the northeastern (Tohoku) area of Honshu was presumably split into some fragments. It is considered that Fossa Magna appeared when they were regrouped into the Japanese Islands later on. Along this border, Japan is divided into the southwest Japan (Eurasia plate) consisting of the ancient strata/rocks (the granite in the palaeozonic/mesozonic systems and the old tertiary zone) and the Fossa Magna area (North American plate) consisting of the new strata (the sedimentary rock and volcanic rock in the new tertiary zone). The sediment extends over some 10km along Fossa Magna, which is a factor contributing to the sediment-related disaster, too. The edge on the west side of Fossa Magna is a group of faults called the “Itoigawa-Shizuoka Tectonic Line” that runs the length of Japan from north to south. The Itoigawa-Shizuoka tectonic line runs almost along the Himekawa River.
The earth that breathes - the North Alps
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