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A boulder choke is a collection of large rocks or rubble that obstructs the passage of a cave or mine. In order to progress through passages cavers often need to negotiate or clear boulder chokes. Boulder chokes can be formed by rockfall, massive earth movement, mining debris, or deposition after storms. They may also form in stream-ways, where the debris surrounding rocks and boulders is removed by water. Due to the nature of their formation boulder chokes may be unstable and can prove difficult to navigate and map due to their complexity. In order to clear a boulder choke the rocks obstructing the passage must be broken up and removed, either mechanically or using a small explosive. Boulder chokes can present a significant danger to cavers, as unstable boulders can unexpectedly move, potentially crushing or trapping cavers. Also, In caves prone to flooding, the narrow and contorted path through boulder chokes can fill up with water quickly, preventing movement past the choke == References == 〔 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Boulder choke」の詳細全文を読む スポンサード リンク
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