Here's why:

* Magma's pressure: Magma is molten rock beneath the Earth's surface. It has immense pressure and seeks to escape to the surface.

* Path of least resistance: As magma rises, it follows the path of least resistance, which is often along existing fractures or weaknesses in the surrounding rocks.

* Erosion and melting: The intense heat and pressure of the magma melt and erode the surrounding rock, creating a vertical channel.

* Formation of the conduit: This channel gradually widens and deepens, forming the conduit or pipe through which the magma will eventually erupt.

This conduit can be quite narrow or extremely wide, depending on the volume of magma and the surrounding rock's composition. It acts as a pathway for magma to ascend to the surface, eventually forming volcanic features like lava flows, ash clouds, or even entire mountains.