Aa lava - Aayogan (English spelling)

Japanese: アア溶岩 - アアようがん（英語表記）aa lava

A type of surface form of basalt-andesitic lava. It is often found on the island of Hawaii, where volcanic activity is active, such as Mauna Loa and Kilauea, and its name is derived from the Hawaiian language. The surface of a'a lava is rough, with rugged coke-like rock fragments rolling around. The lava flow is covered with clinker (small rock chunks) and moves relatively slowly in a narrow river 8 to 15 meters wide. Pahoehoe lava, which is also found in Hawaii and has a smooth basaltic surface, can change to a'a lava when it cools and becomes viscous. However, a'a lava rarely changes to pahoehoe lava. Also, when a'a lava further cools and becomes highly viscous, it becomes lumpy andesitic lava. A'a lava is often found in Japan, such as Mt. Mihara on Izu Oshima, Miyakejima, and the Yakehashiri lava flow (a nationally designated special natural monument) on Mt. Iwate.

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

Japanese:

玄武岩―安山岩質の溶岩の表面形態の一つ。マウナロア山やキラウエア山など，火山活動が活発なハワイ島に多く見られ，名称もハワイ語に由来する。アア溶岩の表面は粗く，ごつごつとしたコークス状の岩片がころがっている。溶岩流はクリンカー（小岩塊）に覆われ，幅 8～15mの狭い川となって比較的ゆっくり進む。同じくハワイで見られる，玄武岩質で表面がなめらかなパホイホイ溶岩が低温化し，粘性を得ると，アア溶岩に変化することがある。しかしアア溶岩からパホイホイ溶岩に変わることはほとんどない。またアア溶岩がさらに低温化・高粘性化すると安山岩質の塊状溶岩となる。アア溶岩は伊豆大島の三原山，三宅島，岩手山の焼走り熔岩流（国指定特別天然記念物）など日本でも多く見られる。

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