Pressure decreases as magma rises.
Pressure increases until the volcano explodes.
Step-by-step explanation:
The reason behind volcanic eruption is extreme weather, tectonic plates, climate change and magma movement. Under beneath of earths crust there are molten rock which is formed because of high temperature at core and they are melted and form a magma.
In magma there are various types of gas present. These gases are carbon dioxide, water vapor and also sulfur dioxide. These gases are stored in chambers of magma and it sealed beneath with lid of rock