<p>Continental crust is thick and relatively buoyant.  Ocean crust is much thinner, and relatively dense.</p>
<p>Hence ocean crust &quot;goes down&quot; more easily, and the density can even help pull the ocean slab due to metamorphism.</p>
<p>In contrast, the continents are almost like floating scum which won't go down! When they collide, you get faulting and folding, and the building up of very thick continental crust. Tibet is the best example today. Yes the Tibetan Plateau is high, but the crust is over 100km thick! (think of an iceberg, most of it is below)</p>

CC BY-SA 4.0
2021-02-03T10:12:39.357Z
Also, trenches on land tend to get filled by erosion.
Erik
CC BY-SA 4.0
2021-02-02T15:10:36.703Z
2021-02-02T15:10:36.703Z
winwaed
<p>As mentioned in another answer:</p>
<blockquote>
<p>Continental crust is thick and relatively buoyant. Ocean crust is much thinner, and relatively dense.</p>
</blockquote>
<p>Let's look at a simulation of what might happen. Here's a figure from &quot;<a href="https://doi.org/10.1016/j.epsl.2010.11.035" rel="nofollow noreferrer">Continental collision and slab break-off: A comparison of 3-D numerical models with observations</a>&quot;:</p>
<p><a href="https://i.sstatic.net/zuUtQ.jpg" rel="nofollow noreferrer"><img src="https://i.sstatic.net/zuUtQ.jpg" alt="enter image description here" /></a></p>
<p>Let's look at this in detail.</p>
<p>You start by having a lithospheric plate consisting of oceanic and continental crust, going to the right, and forming a subduction zone under another lithosphere plate carrying continental crust:</p>
<p><a href="https://i.sstatic.net/QJmZ5.jpg" rel="nofollow noreferrer"><img src="https://i.sstatic.net/QJmZ5.jpg" alt="enter image description here" /></a></p>
<p>Then the oceanic crust keeps going under into the mantle, eventually reaching a stage where both continental crusts are now in contact:</p>
<p><a href="https://i.sstatic.net/HxdjR.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/HxdjR.png" alt="enter image description here" /></a></p>
<p>Finally, the oceanic crust tears or breaks off the continental crust part, and sinks into the mantle, with the surrounding asthenospheric mantle filling up the space. There's no dense oceanic crust to pull everything down to form a trench now, so instead you have mountain ranges and the two plates are amalgamated.</p>

CC BY-SA 4.0
2021-02-04T04:56:18.110Z
also known as the Himalaya
John
CC BY-SA 4.0
2021-02-03T23:32:49.500Z
2021-02-03T23:32:49.500Z
Gimelist
<p>The ocean has some of the deepest locations on earth, typically caused by subduction zones. Why are there no subduction trenches on land?</p>

<plate-tectonics><subduction>
Why are there no subduction trenches on continental land?
joeldesante
# Why are there no subduction trenches on continental land?

(Asked by: username_0 on 2021-02-02)

The ocean has some of the deepest locations on earth, typically caused by subduction zones. Why are there no subduction trenches on land?

**Tags:** plate-tectonics, subduction


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## 2 answers

### Answer by username_1 on 2021-02-02. Score: 5 | Accepted answer

Continental crust is thick and relatively buoyant. Ocean crust is much thinner, and relatively dense.

Hence ocean crust "goes down" more easily, and the density can even help pull the ocean slab due to metamorphism.

In contrast, the continents are almost like floating scum which won't go down! When they collide, you get faulting and folding, and the building up of very thick continental crust. Tibet is the best example today. Yes the Tibetan Plateau is high, but the crust is over 100km thick! (think of an iceberg, most of it is below)

> **Comments:**
> **username_2**: Also, trenches on land tend to get filled by erosion.  

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### Answer by username_3 on 2021-02-03. Score: 4

As mentioned in another answer:

> Continental crust is thick and relatively buoyant. Ocean crust is much thinner, and relatively dense.

Let's look at a simulation of what might happen. Here's a figure from "[Continental collision and slab break-off: A comparison of 3-D numerical models with observations](https://doi.org/10.1016/j.epsl.2010.11.035)":

[![enter image description here](https://i.sstatic.net/zuUtQ.jpg)](https://i.sstatic.net/zuUtQ.jpg)

Let's look at this in detail.

You start by having a lithospheric plate consisting of oceanic and continental crust, going to the right, and forming a subduction zone under another lithosphere plate carrying continental crust:

[![enter image description here](https://i.sstatic.net/QJmZ5.jpg)](https://i.sstatic.net/QJmZ5.jpg)

Then the oceanic crust keeps going under into the mantle, eventually reaching a stage where both continental crusts are now in contact:

[![enter image description here](https://i.sstatic.net/HxdjR.png)](https://i.sstatic.net/HxdjR.png)

Finally, the oceanic crust tears or breaks off the continental crust part, and sinks into the mantle, with the surrounding asthenospheric mantle filling up the space. There's no dense oceanic crust to pull everything down to form a trench now, so instead you have mountain ranges and the two plates are amalgamated.

> **Comments:**
> **username_4**: also known as the Himalaya  

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