Erosion of land caused by ocean water movement such as waves and tidal currents. Rocks that make up land are broken down by waves, and the resulting debris is carried away by tidal currents. Offshore waves are merely the rotational movement of ocean water, but as they approach shallow areas they begin to move and crash into the coast. During storms, the air between the cliff and the waves is trapped and compressed in the seawater as they crash violently into the rocks, seeping into cracks and breaking the rocks into blocks . The pressure exerted by these forces can exceed 1 kg per square centimeter. The blocks are moved by the wave motion and act as tools to destroy the coast, making the destructive force even greater. The topography of the coast is constantly changing due to crustal movement and changes in sea level, but marine erosion further modifies it, creating new coastal topography. Source: Encyclopaedia Britannica Concise Encyclopedia About Encyclopaedia Britannica Concise Encyclopedia Information |
波浪,潮流など海水の運動による陸地の浸食。陸地をつくる岩石は波浪によって破壊され,それによってできた岩屑を潮流が運搬する。沖合いの波浪は海水の回転運動にすぎないが,浅いところに近づくにつれ移動を始め,海岸にぶつかる。暴風時には岸壁と波浪の間の空気を海水中に閉じ込め圧縮しながら激しく岩石にぶつかり,割れ目に浸入して岩石をブロック状にはがす。その際の圧力は,1cm2につき 1kgをこえることがある。ブロックは波動に動かされて,海岸を破壊する道具の役割をするので,破壊力はさらに大きくなる。地殻運動,海面変化などによって海岸付近の地形は絶えず変動するが,海食作用がさらにそれを修正して新たな海岸地形をつくり上げる。
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