< p >,从< a href = " https://en.wikipedia.org/wiki/Oceanic_trench " rel = " nofollow noreferrer " >维基百科< / >:< / p > < blockquote > < p >有几个因素控制沟的深度。最重要的控制是<强>沉积物的供给< / >强,填充沟,这样没有水深的表达式。因此不足为奇了最深的海沟(深度超过8000米(26000英尺))都是nonaccretionary。相比之下,所有的战壕日益增生棱镜浅比8000米(26000英尺)。< / p > < p >二阶控制沟深度<强>岩石圈俯冲时的年龄< / >强。因为海洋岩石圈冷却和变稠的年龄,它消退。年长的海底,更深层次的是,这决定了最小深度的海底开始下降。这种明显的相关性可以被观察的相对深度、区域海底深度和最大沟深度之间的区别。相对深度可能是由岩石圈的年龄控制在海沟,收敛速度和倾斜的俯冲板中间深度。< / p > < p >最后,<强>窄板可以水槽和回滚比广泛迅速板< / >强,潜在的软流层,因为它是容易的边缘绕流板下沉。 Such slabs may have steep dips at relatively shallow depths and so may be associated with unusually deep trenches, such as the Challenger Deep.
A simple picture for anyone who doesn't understand how these trenches form: 
(source: wikispaces.com)
Also, the Mariana Trench isn't the only super deep trench in the ocean... 10 deepest parts of the ocean
