Volcanic Eruption StagesOnline version Sort the eruption stages from start to finish. by Mendoza Rhealyn L. 1 Arrange the process of volcanic eruption from 1st to last. Gas bubbles expand and increase pressure inside the volcano. Magma reaches the Earth’s surface as pressure becomes too strong. Magma gathers and builds up inside the magma chamber. Magma rises toward the Earth’s surface. The volcano erupts. Pressure decreases, causing dissolved gases to form bubbles (vesiculation). Rocks in the mantle melt due to high temperature, forming magma.