Mountain range - sanmyaku (English spelling)

Japanese: 山脈 - さんみゃく（英語表記）mountain range

A mountain range is a continuous vein-like mountain range that runs in a fixed direction. Unlike plateaus and plateaus, large mountain ranges around the world are distributed in specific regions. Examples include the mountain ranges of the Circum-Pacific orogenic belt and the Alpine-Himalayan orogenic belt. The distribution of these two orogenic belts and their relationship to the layout of the continents are explained by the theory of plate tectonics. Mountain ranges around the world are classified based on factors such as their origin, the time of their formation, and their shape and location.

[Takuma Arii]

Classification by origin

Mountain ranges according to this classification are classified as folded mountain ranges and fault mountain ranges. Folded mountain ranges are formed by folding of the geological structure of the mountain range. The great mountain ranges of the world were formed by crustal movement mainly involving folding. The ridges formed by folding are called anticlines, and the valleys are called synclines. Because erosion is constantly occurring on land, there are almost no mountain ranges in which the folded structure is fully reflected in the topography. The Jura Mountains between France and Switzerland are known as an example where the folded structure and the relief of the mountain range are relatively consistent. In many cases, the anticlines of the folds become valleys and the synclines become ridges due to erosion. The relationship between the topography of the mountain ranges and the complex folded structure has been well studied in the Alps, Pyrenees, and Ural Mountains in Europe, and the Appalachians and Rocky Mountains in North America.

A mountain range formed by fault movement is called a fault mountain range. This mountain range is bounded by steep cliffs called fault scarps, which are caused by fault displacement. A tectonic mountain range is a mountain range bounded by fault scarps on both sides (or their edges). Japan has a good number of tectonic mountain ranges, and the Kiso, Akaishi, and Suzuka mountains in Honshu are good examples. A tilted tectonic mountain range is a topography that consists of a fault scarp on one side and a sloping mountain slope on the other side. The Sierra Nevada mountain range in the United States is known as a typical example.

[Takuma Arii]

Division by era

Mountain ranges are sometimes classified according to the geological period in which they were formed, such as the Paleozoic mountain ranges (Paläiden) and the Mesozoic to Cenozoic mountain ranges. Examples of the former are the Caledonian and Hercynian (Variscan) mountain ranges in Europe, and examples of the latter are the mountain ranges of the Circum-Pacific orogenic belt and the Alpine-Himalayan orogenic belt.

[Takuma Arii]

Classification by shape and position

A mountain range that is arranged in such a way that it forms part of a circular arc is called an arc-shaped mountain range. This type of topography is particularly prevalent in the peripheral areas of the Asian continent, including the Japanese archipelago. There are various types, such as anticurved, linked, parallel, staggered, and branched. A mountain range that is located at a major watershed is called a backbone mountain range, and a typical example of this is the Rocky Mountains.

[Takuma Arii]

Major mountain ranges and mountainous areas in Japan
©Shogakukan ">

Major mountain ranges and mountainous areas in Japan

Major Mountains of the World
©Shogakukan ">

Major Mountains of the World

Source: Shogakukan Encyclopedia Nipponica About Encyclopedia Nipponica Information | Legend

Japanese:

連続して脈状に一定の方向に連なる山地をいう。世界における大山脈は、台地や高原と異なり、特定の地帯に分布している。環太平洋造山帯やアルプス‐ヒマラヤ造山帯の山脈群はその例である。この両造山帯の分布と大陸の配置関係は、プレートテクトニクス説で説明されている。世界の各地の山脈は、成因、形成の時代、形や位置などを指標にして区分されている。

［有井琢磨］

成因による区分

この区分による山脈として、褶曲(しゅうきょく)山脈と断層山脈がある。褶曲山脈は、山脈の地質構造が褶曲作用で形成されたものである。世界の大山脈は褶曲運動を主体とする地殻運動で生じたものである。褶曲によって生じた尾根を背斜、谷を向斜とよんでいる。陸上では絶えず侵食作用が働いているので、褶曲の構造が完全に地形に現れている山脈は、ほとんど存在していない。フランスとスイスの間にあるジュラ山脈は、褶曲構造と山脈の起伏が比較的一致した例として知られている。侵食作用を受けて褶曲の背斜部が谷になり、向斜部が尾根になるような場合が多い。ヨーロッパのアルプス山脈・ピレネー山脈・ウラル山脈、北アメリカのアパラチア山脈・ロッキー山脈などでは、山脈の地形と複雑な褶曲構造の関係がよく調査されている。

　断層運動で形成された山脈を、断層山脈とよんでいる。この山脈は、断層変位で生じた断層崖(がい)とよばれる急崖で限られている。地塁山脈は、山脈の両側（またはその周縁）が断層崖で限られた山脈である。日本には地塁山脈の発達が良好であり、本州の木曽(きそ)・赤石・鈴鹿(すずか)などの山脈はその適例である。傾動地塊山脈は、山脈の一方の側が断層崖、他の側は傾いた山地斜面からなる地形である。アメリカのシエラ・ネバダ山脈はその典型として知られる。

［有井琢磨］