<p>The deep zones in the ocean are not where new rock is formed. The trenches are the areas where rock is <em>subducted</em> back into the mantle. Here's a picture to visualise it:</p>

<p><a href="https://i.sstatic.net/1QqHr.png" rel="noreferrer"><img src="https://i.sstatic.net/1QqHr.png" alt="enter image description here"></a><sup><em><a href="https://commons.wikimedia.org/wiki/File:Tectonic_plate_boundaries2.png" rel="noreferrer">USGS/USGov, modified by Eurico Zimbres</a></em></sup></p>

<p>New rock is formed at mid ocean ridges (for example 12 in the image). Those are areas that are less deep than the rest of the ocean. This rocky plate sinks underneath another plate (either continental or oceanic) and by doing so "pulls" that plate down (for example 13 and 18 in the image). This is what causes the extreme depth of those areas.</p>

CC BY-SA 3.0
2016-02-02T01:18:45.797Z
2016-02-02T01:18:45.797Z
Gimelist
<p>Some areas of oceans are about 11 km deep. Is it because continental plates were moving away because of troughs in the middle from where new rock is formed? If so, why did it become deep? If not, what are other reasons?</p>

<geophysics><geology><oceanography><plate-tectonics><subduction>
Why are oceans so deep?
Marijn 
# Why are oceans so deep?

(Asked by: username_0 on 2016-02-01)

Some areas of oceans are about 11 km deep. Is it because continental plates were moving away because of troughs in the middle from where new rock is formed? If so, why did it become deep? If not, what are other reasons?

**Tags:** geophysics, geology, oceanography, plate-tectonics, subduction


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## 1 answers

### Answer by username_1 on 2016-02-02. Score: 5

The deep zones in the ocean are not where new rock is formed. The trenches are the areas where rock is *subducted* back into the mantle. Here's a picture to visualise it:

[![enter image description here](https://i.sstatic.net/1QqHr.png)](https://i.sstatic.net/1QqHr.png)*[USGS/USGov, modified by Eurico Zimbres](https://commons.wikimedia.org/wiki/File:Tectonic_plate_boundaries2.png)*

New rock is formed at mid ocean ridges (for example 12 in the image). Those are areas that are less deep than the rest of the ocean. This rocky plate sinks underneath another plate (either continental or oceanic) and by doing so "pulls" that plate down (for example 13 and 18 in the image). This is what causes the extreme depth of those areas.


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