<p>Both are correct to some degree.</p>

<p>Basalts are usually the result of direct mantle melting, below the crust. This is the case in the famous volcanos of Hawaii and this is also the case in the most common type of volcanism on Earth: the mid-ocean ridges (albeit hidden below several kilometres of sea water).</p>

<p>Most other eruptive rocks (rhyolite, andesite, etc) are usually the result of either melting of the crust, or interaction of mantle melts (basalts) with crustal rocks. A very large portion of these rocks erupt above subduction zones (most obvious example being the <a href="http://education.nationalgeographic.org/encyclopedia/ring-fire/" rel="nofollow">Ring of Fire</a>). The reason is that wet subducting oceanic lithospheres get heated and lose their water. We usually think of water as something that puts out fires, but in the deep Earth it actually lowers the melting point of rocks. This causes melting in the crust, and eventually erupts as volcanoes.</p>

<p>This is a very simplified overview of the subject, and it's a very active area of scientific research with sometimes opposing opinions. But the basic story is somewhat established: some volcanoes (mostly basalts) are products of mantle melting, while others (mostly other stuff) are products of crustal melting.</p>

CC BY-SA 3.0
2016-03-07T08:51:28.783Z
2016-03-07T08:51:28.783Z
Gimelist
<p>Mechanism 1 is mostly correct , though incomplete
It explains most volcanism in the back arc as pulling from the subduction causes the crust to crack and lava to come out
The main volcanic arc however forms when lower melting point crust material sink down ,mixes with mantle material and melt, upon which the magma pushes up and becomes lava</p>
<p>Mechanism 2 is mostly incorrect;Friction melted rock tends to lubricate the rocks and retard further heating</p>

CC BY-SA 4.0
2024-07-06T23:46:02.713Z
When rock is frictionally melted, it ends up reducing pseudotachylite
Harrychink
CC BY-SA 4.0
2024-08-14T11:54:02.940Z
Producing! Not reducing! Typo!!!
Harrychink
CC BY-SA 4.0
2024-08-14T11:54:09.743Z
Why the downvotes?
Harrychink
CC BY-SA 4.0
2024-07-06T13:50:06.607Z
2024-07-07T02:47:30.660Z
2024-07-07T02:47:30.660Z
Harrychink
<p>Neither, Eruptions of extreme magnitude occur when the magnetic field of a planet is slowly depleting due to the upcoming reverse in polarity. The core of the planet will start to liquefy from the high levels of solar radiation because the magnetic field is weakening and not able to block the radiation daily.</p>

<p>So basically its like overcooking a soup at high temperatures, the soup will eventually overflow and spill out.</p>

CC BY-SA 3.0
2016-03-07T08:43:09.773Z
You are definitely not correct.
Gimelist
CC BY-SA 3.0
2016-03-09T15:44:37.893Z
... and you are definitely not even answering the *question*.
Luaan
CC BY-SA 3.0
2016-03-07T07:00:18.770Z
2016-03-07T07:00:18.770Z
user5434678
<p>Ok, it looks like a very simple question but I still have some point want to clarify...</p>

<p>Most images explain volcanos contain some orange stuffs as magma below volcanoes as magma chamber, but the problem is, what is the primary source of the magma? I have 2 assumptions but don't know which is correct:</p>

<ol>
<li><p>Magma is directly supplied from magma below crust, in subduction zone the crust rubs and some cracks formed, magma rushes out from mantle and then to the surface of Earth via cracks.</p></li>
<li><p>The magma is formed by molten crust cause by rubbing and then heating, then it rushes out via cracks. In other words, the magma is originally a part of crust and it just melt again through rubbing, which is not related to the magma below crust.</p></li>
</ol>

<p>Which is correct?</p>

CC BY-SA 3.0
2016-03-07T13:27:03.100Z
Just to clarify; the mantle is **not** molten (for the most part). It is solid and only melts under special circumstances.
bon
<geology><volcanology><petrology>
What is the source of lava of volcano? From magma below crust? Or from molten crust by rubbing?
Gstestso
# What is the source of lava of volcano? From magma below crust? Or from molten crust by rubbing?

(Asked by: username_0 on 2016-03-07)

Ok, it looks like a very simple question but I still have some point want to clarify...

Most images explain volcanos contain some orange stuffs as magma below volcanoes as magma chamber, but the problem is, what is the primary source of the magma? I have 2 assumptions but don't know which is correct:

1. Magma is directly supplied from magma below crust, in subduction zone the crust rubs and some cracks formed, magma rushes out from mantle and then to the surface of Earth via cracks.
2. The magma is formed by molten crust cause by rubbing and then heating, then it rushes out via cracks. In other words, the magma is originally a part of crust and it just melt again through rubbing, which is not related to the magma below crust.

Which is correct?

**Tags:** geology, volcanology, petrology

> **Comments:**
> **username_1**: Just to clarify; the mantle is **not** molten (for the most part). It is solid and only melts under special circumstances.  

---

## 3 answers

### Answer by username_2 on 2016-03-07. Score: 4 | Accepted answer

Both are correct to some degree.

Basalts are usually the result of direct mantle melting, below the crust. This is the case in the famous volcanos of Hawaii and this is also the case in the most common type of volcanism on Earth: the mid-ocean ridges (albeit hidden below several kilometres of sea water).

Most other eruptive rocks (rhyolite, andesite, etc) are usually the result of either melting of the crust, or interaction of mantle melts (basalts) with crustal rocks. A very large portion of these rocks erupt above subduction zones (most obvious example being the [Ring of Fire](http://education.nationalgeographic.org/encyclopedia/ring-fire/)). The reason is that wet subducting oceanic lithospheres get heated and lose their water. We usually think of water as something that puts out fires, but in the deep Earth it actually lowers the melting point of rocks. This causes melting in the crust, and eventually erupts as volcanoes.

This is a very simplified overview of the subject, and it's a very active area of scientific research with sometimes opposing opinions. But the basic story is somewhat established: some volcanoes (mostly basalts) are products of mantle melting, while others (mostly other stuff) are products of crustal melting.


---

### Answer by username_3 on 2024-07-06. Score: -1

Mechanism 1 is mostly correct , though incomplete
It explains most volcanism in the back arc as pulling from the subduction causes the crust to crack and lava to come out
The main volcanic arc however forms when lower melting point crust material sink down ,mixes with mantle material and melt, upon which the magma pushes up and becomes lava

Mechanism 2 is mostly incorrect;Friction melted rock tends to lubricate the rocks and retard further heating

> **Comments:**
> **username_3**: When rock is frictionally melted, it ends up reducing pseudotachylite  
> **username_3**: Producing! Not reducing! Typo!!!  
> **username_3**: Why the downvotes?  

---

### Answer by username_4 on 2016-03-07. Score: -5

Neither, Eruptions of extreme magnitude occur when the magnetic field of a planet is slowly depleting due to the upcoming reverse in polarity. The core of the planet will start to liquefy from the high levels of solar radiation because the magnetic field is weakening and not able to block the radiation daily.

So basically its like overcooking a soup at high temperatures, the soup will eventually overflow and spill out.

> **Comments:**
> **username_2**: You are definitely not correct.  
> **username_5**: ... and you are definitely not even answering the *question*.  

---

