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| Over there was the epicenter. |
Take Tanzawa Mountains 丹沢山地. The steep slopes of the area were once at the bottom of the Ocean whose name was even not Pacific, but Izanagi (the name of creator god for Japanese mythology). Actually, at that time Japanese archipelago did not exist. Many sections of the current Japanese islands were a part of Eurasian Plate. Huge Pressure caused by the crash of Eurasian, Philippine Sea, and North American Plates bended and torn up the upper part of the crusts. The ripped former parts of Eurasian and North American Plates were folded further that make the base of Honshu Island. When the seabed, including the present-day Tanzawa, kept on pushing the Eurasian Plate, the split part from the Eurasian Plate was bended 90° degree, and the huge area of the crust fell to form a huge valley. The dent induced a gigantic gash of sea water inland and created the origin of Japan / East Sea. Along the “shores” of newly born inland sea, the chains of volcanos activated and repeated violent eruptions.
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| Tanzawa Mountains are getting taller day by day. |
The western part of the valley’s shore has now clearly been identified by mortal humans as an enormous fault line slicing Honshu Island. It starts from Itoigawa City 糸魚川市 on Sea of Japan / East Sea side and goes through Sizuoka City 静岡市 on Pacific Ocean side. The fault line is called Itoigawa-Shizuoka Tectonic Line. (Er, well, no surprise for this name.) In contrast, the exact location of the eastern shore of the valley is under a lively debate among scholars. One thing is sure. The area sandwiched by these two shores is a region considered to have one of the most active volcanic mountains on earth. The area has a name, Fossa Magna. Tectonic crushes make fissures on the earth’s crust. The mantle of the planetary core finds corridors to release its heat et al and melts the upper layer of the planet. Lava is made deep down, and it comes up and forms lots of lava pools which could eventually become volcanoes. Tanzawa Mountains are on one of the lava pools since they were undersea.
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| And so, there is Mt. Fuji. |
Itoigawa-Shizuoka Tectonic Line sliced Shizuoka City continues to Suruga Bay, the deepest Bay in the Japanese territory. When the Tectonic Line dived in the Pacific Ocean, it has another name, Suruga Trough. The northern march of Philippine Sea Plate first created bulges of volcanic seabed. The underwater world had lots of eruptions spewing lapilli and ashes into the Ocean. These minerals piled up on the seabed, another eruption occurred with extreme heat, the accumulated minerals were melted, and then they were cooled by seawater. The proceed of tectonic crush continuously pushed volcanic strata beneath the Eurasian Plate. The layers went through a humongous press machine, aka the tectonic plates, and eventually sprung back upwards at the edge of tectonic crushes. Earthquake! After such shock, the seabed ended up as an island, and continued going north on Philippines Sea Plate, while occasional under/over sea volcanic eruptions.
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| On the Philippines Sea Plate, Enoshima Island is standing-by for a crush. |
At the end of the day, the island collided with part of the Eurasian Continent. First, the collision made very shallow sea between the Eurasian Plate and the island. It was shallow enough to be filled easily by sediments coming down from the continent and the island, while the sea became smaller as the island proceeded further. The sea was reclaimed, and the island was getting taller and taller. The Tanzawa Mountains were born. i.e. The soil of Tanzawa Mountains is made of volcanic sediments raised from the seabed where the undersea volcanos spewed lava et al.
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| The fossils
of Smooth Cauliflower Coral found in deep Tanzawa Mountains of Yamakita Town. The place was once under sea … |
Such origin of Tanzawa is observable from rocks we find in, say, Yadoriki Stream. Next week, I show you my collection of rocks from Yadoriki. They are beautiful, I tell you. Please stay tuned!
If you find environmental issues in Kanagawa Prefecture, please make a contact with Kanagawa Natural Environment Conservation Center 神奈川県自然環境保全センター
657 Nanasawa, Atsugi City, 243-0121
〒243－0121 厚木市七沢657
Phone: 046-248-0323
You can send an enquiry to them by clicking the bottom line of their homepage at http://www.pref.kanagawa.jp/div/1644/
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