<h1>The height of the Himalayas</h1>

<p>Like Keith McClary says in his answer, there really are two factors in creating growing/shrinking mountains.</p>

<ol>
<li><a href="https://en.wikipedia.org/wiki/Mountain_formation" rel="noreferrer">Mountains grow</a> due to various reasons. In the case of the Himalayas it's like you must've seen in the documentary: the collision between the Indian and Eurasian continental plates. The material has to go somewhere and thus goes up (simplifying the geology a bit; I think that concepts like buoyancy these days also give some nuance to the subject, but the general picture stays the same). In the Himalayas, the two plates have moved into each other for at least 2500 km, so that's a lot of ground to move!</li>
</ol>

<p><a href="https://i.sstatic.net/bbgFL.gif" rel="noreferrer"><img src="https://i.sstatic.net/bbgFL.gif" alt="mountain_formation"></a></p>

<ol start="2">
<li>If that was the only process at play, there would be <em>way</em> higher mountains. I couldn't find a corresponding figure for the Himalayas, so consider instead the following present-day profile through Switzerland, running roughly north (left) to south (right).
<a href="https://i.sstatic.net/WJTGQ.jpg" rel="noreferrer"><img src="https://i.sstatic.net/WJTGQ.jpg" alt="Alps-north-south-profile"></a>
You can see that the present-day Alps are at maximum 4 km high. Compare that against a reconstruction of the geology that <em>should be</em> present, running along basically the same profile:
<a href="https://i.sstatic.net/U9V7V.jpg" rel="noreferrer"><img src="https://i.sstatic.net/U9V7V.jpg" alt="Alps-full-geology"></a></li>
</ol>

<p>You can see that the mountains could be as much as 20 km high! You can appreciate just how much mountain has disappeared, for another very young mountain range! So, the reason that mountains aren't as big as they could/should have been, is that they are cut down by <a href="https://en.wikipedia.org/wiki/Erosion" rel="noreferrer">erosion</a>. Rain, snow, wind, temperature, all break down mountainous rocks into smaller broken pieces. Those pieces are transported away from the mountains as <em>sediment</em> in rivers (such as the Yangtze for the Himalayas).</p>

<p>So, the height of the Himalayas is very much controlled by the relative size of the two effects: how fast does the mountain range grow, and how fast does erosion break it down again. If the two are in equilibrium, the mountain doesn't shrink or grow. If erosion dominates, the mountain will slowly disappear over time. But in the case of the Himalayas, the mountain building generally outpaced the erosion, leading to the unique heights of the Himalayas. In this case, the speed of the collision is definitely the main factor!</p>

<h1>The size of the Tibetan Plateau</h1>

<p><a href="https://i.sstatic.net/upnIS.gif" rel="noreferrer"><img src="https://i.sstatic.net/upnIS.gif" alt="Himalayas-geology"></a><a href="https://i.sstatic.net/VgIZY.jpg" rel="noreferrer"><img src="https://i.sstatic.net/VgIZY.jpg" alt="convergence"></a></p>

<p>Now if your question was also about why the Tibetan Plateau is so <em>wide</em> (rather than the Himalayas so <em>high</em>), I recommend you read <a href="https://oak.ucc.nau.edu/wittke/Tibet/Plateau.html" rel="noreferrer">https://oak.ucc.nau.edu/wittke/Tibet/Plateau.html</a> , a very well-written summary of the three main hypotheses:</p>

<ol>
<li>The speed of the collision has lead to a very step-wise straight faults toppling over each other, rather than folding over, which could lead to very long faulted sections. "<em>Crust is thickened by the faulting and subsequent movement of large masses of rock, which are stacked one on top of another like cordwood.</em>"</li>
<li>When India hit the Eurasian plate it still had a heavy oceanic plate that was going under ('subducting') under the Eurasian plate. Now the oceanic plate has disappeared, and now the continental plate is being pulled underneath the Eurasian plate. "<em>This process is reminiscent of taking a block of ice and pushing it beneath another ice slab, causing the latter to rise upwards. However, it is difficult to imagine how the buoyant Indian crust could be kept deep enough to get far beneath the plateau before bobbing to the surface. Perhaps the great speed at which India is colliding to Eurasia allowed this to happen.</em>"</li>
<li>The last hypothesis is simply that the continental collision puts a lot of heat below the plateau. "<em>Like a hot-air balloon, the heated crust is buoyant and rises with the addition of light granitic material at the bottom of the Eurasian crust increasing the height of the Plateau.</em>"</li>
</ol>

<p>This picture shows all those three hypotheses. 1=distributed shortening, 2=underthrusting, 3=lower crustal flow. In each case, a plateau is formed relatively far away from the actual collision between the two plates.
<a href="https://i.sstatic.net/fjU4f.png" rel="noreferrer"><img src="https://i.sstatic.net/fjU4f.png" alt="enter image description here"></a></p>

<p>It is likely that, really, all three hypotheses together are at play. As explained on the website, at least the first two hypotheses are thought to be related to the speed of the collision.</p>

<p>So, yes, both the height and the width of the Himalayas are thought to be linked to the speed of the collision/relative plate movement!</p>

CC BY-SA 4.0
2020-06-20T04:34:11.510Z
This suggests that erosion is less important: [Plate tectonics vs. erosion—what sets the height of a mountain range?](https://arstechnica.com/science/2020/06/plate-tectonics-vs-erosion-what-sets-the-height-of-a-mountain-range/).
Keith McClary
CC BY-SA 4.0
2020-02-16T07:48:53.407Z
2020-02-16T16:09:13.737Z
2020-02-16T16:09:13.737Z
Erik
<p>In an episode of History Channel's <em>How the Earth Was Made</em>, there was a remark when India left the rest of Gondwana 80 million years ago only to collide with mainland Asia 50.5 million years ago.  The remark was, "very fast in geological time."  Afterwards, it was said that "as with any smash, the faster the collision, the bigger the wreck."  In the episode, those remarks were written as an explanation for the Himalayas' "unique size".</p>

<p>But is this true?  Could the speed in which one plate collides with another REALLY affect the size of a mountain range?</p>

CC BY-SA 4.0
2020-02-15T04:26:02.350Z
I've heard that the Himalayas are (still) rising faster than erosion can grind them down. It looks [complicated](https://www.google.com/search?client=ubuntu&channel=fs&q=Himalayas+uplift+rate+erosion).
Keith McClary
CC BY-SA 4.0
2020-04-08T16:02:39.830Z
@KeithMcClary: This anecdote is physically meaningless. A Snickers bar at what velocity?
AtmosphericPrisonEscape
CC BY-SA 4.0
2020-04-10T00:51:50.707Z
it is not the rate at which they collided, it is the rate at which they collided and are still colliding. it is simple math conceptually the rate at which they are being pushed up minus the rate of erosion times how long it has been occurring .
John
CC BY-SA 4.0
2020-04-11T11:56:38.847Z
Please do not revert the title edit again, or we will lock the question such that it cannot be edited at all.
gerrit
<plate-tectonics><mountains><mountain-building>
Could the speed in which the plate is moving affect how quickly mountains rise?
JohnWDailey
# Could the speed in which the plate is moving affect how quickly mountains rise?

(Asked by: username_0 on 2020-02-13)

In an episode of History Channel's *How the Earth Was Made*, there was a remark when India left the rest of Gondwana 80 million years ago only to collide with mainland Asia 50.5 million years ago. The remark was, "very fast in geological time." Afterwards, it was said that "as with any smash, the faster the collision, the bigger the wreck." In the episode, those remarks were written as an explanation for the Himalayas' "unique size".

But is this true? Could the speed in which one plate collides with another REALLY affect the size of a mountain range?

**Tags:** plate-tectonics, mountains, mountain-building

> **Comments:**
> **username_1**: I've heard that the Himalayas are (still) rising faster than erosion can grind them down. It looks [complicated](https://www.google.com/search?client=ubuntu&channel=fs&q=Himalayas+uplift+rate+erosion).  
> **username_2**: @username_1: This anecdote is physically meaningless. A Snickers bar at what velocity?  
> **username_3**: it is not the rate at which they collided, it is the rate at which they collided and are still colliding. it is simple math conceptually the rate at which they are being pushed up minus the rate of erosion times how long it has been occurring .  
> **username_4**: Please do not revert the title edit again, or we will lock the question such that it cannot be edited at all.  

---

## 1 answers

### Answer by username_5 on 2020-02-16. Score: 11 | Accepted answer

# The height of the Himalayas

Like username_1 says in his answer, there really are two factors in creating growing/shrinking mountains.

1. [Mountains grow](https://en.wikipedia.org/wiki/Mountain_formation) due to various reasons. In the case of the Himalayas it's like you must've seen in the documentary: the collision between the Indian and Eurasian continental plates. The material has to go somewhere and thus goes up (simplifying the geology a bit; I think that concepts like buoyancy these days also give some nuance to the subject, but the general picture stays the same). In the Himalayas, the two plates have moved into each other for at least 2500 km, so that's a lot of ground to move!

[![mountain_formation](https://i.sstatic.net/bbgFL.gif)](https://i.sstatic.net/bbgFL.gif)

2. If that was the only process at play, there would be *way* higher mountains. I couldn't find a corresponding figure for the Himalayas, so consider instead the following present-day profile through Switzerland, running roughly north (left) to south (right).
   [![Alps-north-south-profile](https://i.sstatic.net/WJTGQ.jpg)](https://i.sstatic.net/WJTGQ.jpg)
   You can see that the present-day Alps are at maximum 4 km high. Compare that against a reconstruction of the geology that *should be* present, running along basically the same profile:
   [![Alps-full-geology](https://i.sstatic.net/U9V7V.jpg)](https://i.sstatic.net/U9V7V.jpg)

You can see that the mountains could be as much as 20 km high! You can appreciate just how much mountain has disappeared, for another very young mountain range! So, the reason that mountains aren't as big as they could/should have been, is that they are cut down by [erosion](https://en.wikipedia.org/wiki/Erosion). Rain, snow, wind, temperature, all break down mountainous rocks into smaller broken pieces. Those pieces are transported away from the mountains as *sediment* in rivers (such as the Yangtze for the Himalayas).

So, the height of the Himalayas is very much controlled by the relative size of the two effects: how fast does the mountain range grow, and how fast does erosion break it down again. If the two are in equilibrium, the mountain doesn't shrink or grow. If erosion dominates, the mountain will slowly disappear over time. But in the case of the Himalayas, the mountain building generally outpaced the erosion, leading to the unique heights of the Himalayas. In this case, the speed of the collision is definitely the main factor!

# The size of the Tibetan Plateau

[![Himalayas-geology](https://i.sstatic.net/upnIS.gif)](https://i.sstatic.net/upnIS.gif)[![convergence](https://i.sstatic.net/VgIZY.jpg)](https://i.sstatic.net/VgIZY.jpg)

Now if your question was also about why the Tibetan Plateau is so *wide* (rather than the Himalayas so *high*), I recommend you read <https://oak.ucc.nau.edu/wittke/Tibet/Plateau.html> , a very well-written summary of the three main hypotheses:

1. The speed of the collision has lead to a very step-wise straight faults toppling over each other, rather than folding over, which could lead to very long faulted sections. "*Crust is thickened by the faulting and subsequent movement of large masses of rock, which are stacked one on top of another like cordwood.*"
2. When India hit the Eurasian plate it still had a heavy oceanic plate that was going under ('subducting') under the Eurasian plate. Now the oceanic plate has disappeared, and now the continental plate is being pulled underneath the Eurasian plate. "*This process is reminiscent of taking a block of ice and pushing it beneath another ice slab, causing the latter to rise upwards. However, it is difficult to imagine how the buoyant Indian crust could be kept deep enough to get far beneath the plateau before bobbing to the surface. Perhaps the great speed at which India is colliding to Eurasia allowed this to happen.*"
3. The last hypothesis is simply that the continental collision puts a lot of heat below the plateau. "*Like a hot-air balloon, the heated crust is buoyant and rises with the addition of light granitic material at the bottom of the Eurasian crust increasing the height of the Plateau.*"

This picture shows all those three hypotheses. 1=distributed shortening, 2=underthrusting, 3=lower crustal flow. In each case, a plateau is formed relatively far away from the actual collision between the two plates.
[![enter image description here](https://i.sstatic.net/fjU4f.png)](https://i.sstatic.net/fjU4f.png)

It is likely that, really, all three hypotheses together are at play. As explained on the website, at least the first two hypotheses are thought to be related to the speed of the collision.

So, yes, both the height and the width of the Himalayas are thought to be linked to the speed of the collision/relative plate movement!

> **Comments:**
> **username_1**: This suggests that erosion is less important: [Plate tectonics vs. erosion—what sets the height of a mountain range?](https://arstechnica.com/science/2020/06/plate-tectonics-vs-erosion-what-sets-the-height-of-a-mountain-range/).  

---

