Volcanic bomb - Kazandan (English spelling) bomb

Japanese: 火山弾 - かざんだん（英語表記）bomb

This refers to volcanic lapilli and volcanic blocks with a diameter of 2 mm or more that are formed by the wind pressure during flight and the impact when they reach the ground. The final shape is determined by the size, amount, viscosity, and flight speed of the lava at the time of release, but most are spindle-shaped, spherical, or ribbon-shaped, and if they have not cooled and solidified by the time they land, they become flattened and become cow dung-like or dish-like. In addition, if the outside is cooled and solidified suddenly while the inside remains plastic, the gas inside may expand and cause bread crust-like cracks on the surface. Volcanic bombs are characteristic of Strombolian and Vulcanian eruptions.

Source: Encyclopaedia Britannica Concise Encyclopedia About Encyclopaedia Britannica Concise Encyclopedia Information

Japanese:

火山の噴火で放出された未固結の溶岩が，飛来中の風圧や地表到達時の衝撃で，特定の外形（構造）をもつようになった直径 2mm以上の火山礫および火山岩塊をさす。最終的な形状は，放出時の溶岩の大きさや量，粘度，飛翔速度によって決まるが，多くは紡錘状，球状，リボン状の形をなし，着地の際に冷え固まっていない場合は平たくなって牛糞状，皿状となる。また，外側が急に冷やされて固化し，内側が可塑性を保っている場合，内部のガスが膨張して，表面にパン皮状のひび割れを生じることもある。火山弾はストロンボリ式噴火，ブルカノ式噴火に特徴的である。

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