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Izu Peninsula Geopark
About Izu Peninsula Geopark
Geo-historical schemeIsolation from the Continent: The formation of Japanese island arc
Let me remind you how the Japanese Island Arc was developed so that you are able to understand that the specific evolutional history of the Izu Peninsula. The Japanese Island Arc extends similar with boomerang-shape. The center of the “Boomerang” may locate at Tokyo area. The arc seems to be bending, do you know why?
Former Japanese Island Arc had attached to the east edge of the Eurasian Continent at the time of the Cretaceous when dinosaurs were alive. As time goes by, volcanic activities became severe due to the subduction of the oceanic plate ca. 25 Ma before, and then the edge of the continent started to apart. A mediterranean sea developed between the continent and the island arc, and the sea became the Sea of Japan. The arc separated into two blocks and rotated similar with opening door. Finally, the arc settled at the position same as today ca. 14 Ma before. At this time, the Izu block located far away from the Island Arc. Geological history of the Izu Peninsula is able to date back ca. 20 Ma before.
In the initial of the Izu Peninsula, it located at about 800 km south, nearby the tropic of Cancer. At that time, Izu was volcanic groups at the deep sea ocean. The Pacific plate subducts under the Philippine Sea plate, and this subduction supplies magma which requires to develop the Izu Peninsula. On the other hand, the Philippine Sea plate subducts under the Eurasian plate on which the mainland of Japan puts. Submarine volcanos and volcanic islands drifted due to northward shift of the Philippine Sea plate. Finally the block was collided with the mainland, and it formed the peninsula same as today ca. 600 ka before.
Since the formation of the peninsula till 200 ka before, volcanic erupted almost the whole of the peninsula and large scale terrestrial volcanoes had formed that we are able to see in the peninsula today.
In the eastern part of the peninsula, the independent monogenetic volcanoes of the Izu Tobu volcano group eruption continued until today. Continuous movement of the Philippine Sea plate cause the crustal shorting causes the collision orogeny and volcanisms as well as faulting activities. These geological characteristics forms the sceneries and landscape of the Izu Peninsula. Then the Izu Peninsula is the only place in the world that two active volcanic arcs meet. The Izu peninsula extends about 60 km southward from the central part of the mainland of Japan. It has a maximum east-west width of 40 km, and a total coastal length of 318 km. Most of the area is covered by moderate mountains. The highest peak is Mt. Banzaburo (1405 m asl) in the Amagi Mountains. The protrusion of these mountains causes heavy rain. This complex landscape also develops scenic diversity between and within areas.
Sagami bay, located to the east of the peninsula, has a depth of 1000~1500m off the shore. Suruga bay in the west is still deeper, 2500m in the baymouth between Irozaki and Omaezaki. These deep bays are influenced by water coming in from outlying oceanic systems.
The Kanogawa River is the longest river of the peninsula (46 km length). In the lower parts of the Kano plain, the width of the river narrows due to the inflow of volcanic ejecta and debris flow, and it tends to flood during heavy rain and typhoons. The peninsula poorly develops large river systems except the Kanogawa river. The deep waters near the coast and different temperature ranges and water qualities in the bays make these water bodies rich fishing grounds. According to the Köppen-Geiger classification, the Izu peninsula is located in the temperate humid climate zone, as with most locations in Japan. However, the climate within the peninsula varies appreciably between the coastal and interior parts. The coastal regions are influenced by the warm Kuroshio current and have a mean annual temperature of 15–17 ºC; the southern tip of Irozaki Cape does not receive any snowfall even in the winter. In contrast the northern Tagata plain has a wide difference between day and night temperatures, and winter in this area is noticeably colder. The central Amagi highland receives a flow of humid air from the Pacific, resulting in high levels of precipitation (over 4000 mm/year at Mt Amagi) and frequent snowfall during winter. On the other hand the western part of the peninsula is relatively dry due to the prevailing winds depositing their moisture content over the central highlands. Compared to the Tokyo metropolitan area, the coastal areas are warm in winter and cool in summer. The climatic diversity of the peninsula directly contributes to its biodiversity. The Amagi Mountains is known for its forests of deciduous broadleaf trees such as Japanese Beech and Aceraceae family. In particular, it is unusual to find a Fagus crenata forest on the Pacific coast. A diverse range of marine organisms, mostly native to a warm marine environment, can be found in the sea around the peninsula. The Japanese Spider Crab is the largest crab species in the world, and it lives in the deep Suruga bay to the west of Izu. The Izu Peninsula Geopark Promotion Council is composed of a General Assembly, an Executive Committee, the Promotion Council Bureau, and a number of Working committees. The General Assembly is made up of representatives of all the member organizations, and meets once a year to set regulations, strategy, and budget, and to discuss other important issues. The Executive Committee investigates issues to be submitted to the General Assembly, and is responsible for putting plans into effect. The Promotion Council Bureau carries out day-to-day work on the ground and serves as a contact point for the Geopark. The Working committees provide specialist support, and at present there are four: Geoconservation, Geotourism, Education, and Academic Research. The Academic Research Working Group supports these scholarly activities, and has 17 members drawn from the natural sciences, including the geosciences and ecology, social sciences, archaeology, and conservation. The Education Working Group is primarily a contact body with local schools, and both shares information and holds meetings to present the results of educational activities. Geopark support membership program for indivisuals and businesses has been offered. For individuals, if you are interested in geoscience or geopark, with a particular focus on the Izu peninsula, you can attend geotours or geopark events. For business, you can put a geopark logo mark on your own products, link your website to ours and get information of geopark events by e-mail. If you need more information, please feel free to https://english.izugeopark.org/contact/
Must see sights
Tanna fault park
Shift that occurred during the Northern Izu Earthquake, underground structure of the fault, three-dimensional model of the Tanna Fault.
The shift of the fault that occurred during the Northern Izu Earthquake of 1930 is preserved in the Fault Park. Here visitors can observe with their own eyes that as a result of a left-lateral fault movement, the waterway of the time shifted about 2 meters along the fault. Visitors can also see the rupture of the strata in the observation facility offering the viewer a very real demonstration of the fault movement.
Lava flow and columnar joints of Noborio-Minami Volcano; strata of the submarine volcano covered with lava flow
Kamadaru presents a great sight of water cascading down a mass of lava that was itself in motion long ago. Massive joints are also visible around the waterfall. These joints form in the directions along which lava cools (which are usually the upper part exposed to the air and the lower part in contact with the ground).
The columnar joints of Kamadaru Falls have intricate shapes as they are made of lava which flowed through the bottom of the valley.
Pillow lava and magmatic dykes of the Nishina group
Most of the Nishina group of soil strata, which is the oldest strata found on the Izu Peninsula, is lava and subaqueous volcaniclastic flow ejected during the submarine volcanic phase.
When low-viscosity lava flows down the sea bed, it forms a pillow like shape due to surface tension and rapid cooling upon water contact. This is called ‘pillow lava’. In Isshiki, you can seecross-sections of multi-layered pillow lava.
Surface structure and profile of the Omuroyama Volcano lava flow; landscape of Jogasaki Coast
In Kadowakizaki, visitors can enjoy the dynamic landforms of Jogasaki formed by the Omuroyama Volcano.
From suspension bridges hanging over the undulating coastline, one can see “columnar joints”- rocks shaped like columns that form when lava cools down and contracts.
One can also see the marks left by new hot lava as it flowed onto and broke apart the patches of old lava that had already cooled down and solidified.
The Kadowaki Lighthouse also offers a beautiful panorama of the coast and the Omuroyama volcano.