Joint - Setsuri (English spelling)

Japanese: 節理 - せつり（英語表記）joint

A crack is a group of cracks that develop widely in a rock body, and the two sides of the crack do not move apart. When igneous rock cools and contracts, or when the earth's crust moves, stress acts inside the rock, and cracks form as a result. It is thought that when rocks deep underground rise to the surface, pressure is released, causing cracks to develop in the rock. Some cracks are irregular, while others are regularly arranged. Even in regular cracks, the spacing between the cracks varies from a few centimeters to a few meters. Based on the arrangement, they are called columnar joints (Genbudo Cave in Hyogo Prefecture, Keyano Ooto in Fukuoka Prefecture, and Nanatsugama in Karatsu, Saga Prefecture), plate joints (Teppeishi from Nagano Prefecture, Tatami Ishi from Yashima in Kagawa Prefecture, and Gacho Ishi from Shodoshima), radial joints (Kuruma Ishi from Nemuro, Hokkaido), square joints (Koshikake Ishi from Kiso River in Nagano Prefecture), and spherical joints. In terms of origin, they are divided into fracture joints caused by tensile stress and shear joints caused by shear stress that intersects at an acute angle with the direction of maximum compressive stress. Joints are used for quarrying and tunnel excavation, but because they act as channels for groundwater or seepage water, weathering and erosion progress quickly, and are deeply related to the collapse of rocks.

[Saito Yasuji]

Genbudo Cave
Columnar joints exposed on rock faces. San'in Kaigan National Park. Nationally designated natural monument. Toyooka City, Hyogo Prefecture. ©San'in Kaigan Geopark Promotion Council ">

Genbudo Cave

Seven pots
A group of sea caves created by erosion by the rough waves of the Genkai Sea. The larger sea caves are 3m wide, 3m high, and 100m deep. Genkai Quasi-National Park. Nationally designated natural monument. Karatsu City, Saga Prefecture. © Saga Tourism Federation .

Seven pots

Nemuro Wheel Stone
These strangely shaped basaltic rocks are found scattered along the coastline around Cape Hanasaki in the southern part of the Nemuro Peninsula. They are radial joints that were formed when pillow lava was formed in the ocean in ancient times, and are called "Kurumaishi" (wheel stones) because their shape resembles a wheel. The largest one is about 6m in diameter. Nationally designated natural monument Nemuro City, Hokkaido © Nemuro City Tourism Association ">

Nemuro Wheel Stone

Source: Shogakukan Encyclopedia Nipponica About Encyclopedia Nipponica Information | Legend

Japanese:

岩石体に広く群をなして発達している割れ目のことで、それを境に両側がずれ動いていないものをいう。火成岩が冷却して収縮するときや地殻変動を受けたときなどに、岩体内部に応力が働き、その結果生じた割れ目である。地下深部の岩体が隆起して地表へ上昇してくると、圧力が解放されるため、岩体に割れ目が発達すると考えられている。不規則なものや規則正しい配列をしているものがある。規則正しいものでも、割れ目の間隔は数センチメートルから数メートルのものなどいろいろである。配列の形から、柱状節理（兵庫県玄武洞(げんぶどう)、福岡県芥屋ノ大門(けやのおおと)、佐賀県唐津(からつ)の七ツ釜(がま)）、板状節理（長野県産の鉄平石、香川県屋島の畳(たたみ)石、小豆島(しょうどしま)の画帳石）、放射状節理（北海道根室の車(くるま)石）、方状節理（長野県木曽(きそ)川の腰掛(こしかけ)石）、球状節理などとよばれる。成因的には、引張り応力による破断節理、最大圧縮応力の方向に鋭角に交わる剪断(せんだん)応力による剪断節理に分けられる。節理は採石や坑道掘進に利用されるが、地下水あるいは浸透水の流路となるため風化や侵食作用が早く進み、岩石の崩壊に深く関連している。

［斎藤靖二］

[参照項目] | 応力 | 火成岩 | 岩石 | 芥屋ノ大門 | 玄武洞 | 地殻変動 | 鉄平石 | 七ツ釜

玄武洞
岩壁に露出する柱状節理。山陰海岸国立公園域。国指定天然記念物　兵庫県豊岡市©山陰海岸ジオパーク推進協議会">

玄武洞

七ツ釜

根室車石

出典　小学館　日本大百科全書(ニッポニカ)日本大百科全書(ニッポニカ)について　情報 | 凡例

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