Heat cloud - Netsuun

Japanese: 熱雲 - ねつうん

① glowing avalanche, glowing cloud, glutwolke : During an eruption, hot magma is expelled from the crater, mixes with a large amount of gas, and forms a thick mixture of volcanic gas and pyroclastic debris that travels down the slopes of a volcano at very high speed. In 1902, a hot cloud erupted from the middle of a newly formed lava dome on the summit of Mont Pelee volcano on the island of Martinique in the West Indies. When it first erupted, it was over 1,100°C and traveled down the mountainside at an average speed of 11-27 meters per second, with a maximum speed of 150 meters, all the way to the coast, destroying the town of St. Pierre. In 1902, Lacroix named small high-temperature pyroclastic flows that occurred at Pelée and Soufriere volcanoes as nuee ardente [Lacroix: 1904, 1930]. After Lacroix, the term "nuee ardente" was used for other pyroclastic flows, and the definition gradually became confused. As a result, it has been given a variety of names, including glowing claud (Fenner), volcanic blast (Day & Allen), horizontal blast (Day & Allen), hot cloud (Allen & Zies), Glutowolde [Wolff: 1914], hot avalanche [Perret: 1924], avalanche of incandescent cloud (Fenner), absteigend eruptionwolde (Wolff), pellesche wolke (Wolff), new ardente (Lacroix), new peleenne (Lacroix), new dense (Lacroix), ash flow, and fire avalanche.
② nuee ardante : An incandescent mass of gas, steam, and solid volcanic debris released from a volcano. Lacroix distinguishes between pyroclastic clouds: (1) Pele type, which is a direct lateral explosion from the inner crater, (2) Vulcanian type, which is a vertical explosion from the crater, and (3) Katmai type, which is an explosion from a crack in the mountainside. The lower part of the pyroclastic cloud is mostly composed of pyroclastic material and is similar to an ash flow [Lacroix: 1904, 1930]. The French word nuee ardante means a scorching hot cloud. Lacroix gave this name to small high-temperature pyroclastic flows that occurred at Pelee and Soufriere volcanoes in 1902 [Lacroix: 1904, 1930]. Since then, the definition has become increasingly confused. Glowing avalanche, glowing cloud, glutwolke, Glutowolde [Wolff: 1914], hot avalanche [Perret: 1924], etc. are all used with the same meaning.

Source: Asakura Publishing Dictionary of Petrology Information

Japanese:

① glowing avalanche, glowing cloud, glutwolke: 噴火の際に，マグマが高温度のままで火口から放出され，多量のガスと混合して非常な高速で火山体の山腹の斜面を這って走り下る厚い火山ガスおよび火山砕屑物の緻密な混合物．1902年に西インド諸島のマルティニク（Martinique）島のモン・ペレ（Mont Pelee）火山頂上に新しくできた熔岩円頂丘の中腹を破って噴出した熱雲は，噴出当初は1 100℃以上の温度で，平均秒速11～27m，最大150mで山腹を下り海岸まで達してサン・ピエール（St. Pierre）の町を全滅させた．1902年にペレ火山とスーフエリール（Soufriere）火山に発生した小型の高温火砕流にラクロアがヌエ・アルダン（nuee ardente）と命名した［Lacroix : 1904, 1930］．ラクロアの後に他の火砕流にも熱雲が使われ，次第に定義が混乱した．そのため様々名称が付けられており，glowing claud（Fenner）, volcanic blast（Day & Allen）, horizontal blast（Day & Allen）, hot cloud（Allen & Zies）, Glutowolde［Wolff : 1914］，hot avalanche［Perret : 1924］avalanche of incandescent cloud（Fenner）, absteigende Eruptionswolde（Wolff）, pellesche wolke（Wolff）, nuee ardente（Lacroix）, nuee peleenne（Lacroix）, nuee dense（Lacroix）, ash flow, fire avalancheなど多数の名称がある．
② nuee ardante: 火山から放出されたガス，水蒸気，火山の固体破片の白熱した塊のことである．ラクロアは熱雲を(1) ペレ型は噴火口の内火山から側方に直接爆発したもの，(2) ブルカノ型は噴火口から垂直方向に爆発したもの，(3) カトマイ型は山腹の割れ目から爆発したもの，に区別している．熱雲の下部は大部分が火山砕屑物から構成され，火山灰流のようなものである［Lacroix : 1904, 1930］．フランス語のnuee ardanteは灼熱した雲の意味．1902年にペレ（Pelee）火山とスーフリール（Soufriere）火山に発生した小型の高温火砕流にラクロアが命名した［Lacroix : 1904, 1930］．その後次第に定義が混乱してきた．glowing avalanche, glowing cloud, glutwolke, Glutowolde［Wolff : 1914］, hot avalanche［Perret : 1924］などはすべて同じ意味で使われている．

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