What is the source of lava of volcano? From magma below crust? Or from molten crust by rubbing?

Question

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?

Answer 1

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). 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 2

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.