However, magma is not found everywhere on Earth. Magma is formed in a specific area of the earth.
For example, magma is always formed in places like the basement of Japan. Japan's subsurface is a place where a plate-like rock called a plate penetrates into the earth.
The other is called an ocean ridge, which is a mountain range at the bottom of the ocean. It is known that magma is also formed under these undersea mountain ranges.
In such areas, magma is said to be formed at depths ranging from several tens to 200 km below the surface, but since humans cannot drill that deep, we do not yet know exactly how magma is formed.
However, we now know a little bit about how magma is formed. It seems that where magma is formed, the rock is always melting a little. In other words, think of it like ice water. Ice is rock and water is magma. In the area several tens to 200 km below the surface, the rocks are in this state of slight melting. When this magma collects and spews out onto the ground, it is lava, which is called a volcanic eruption.
However, it is still unclear why rocks melt deep underground.
Humans have only been able to drill holes in the earth for about 10 km. For this reason, there are still many things we do not know about the inside of the earth.