If the lava within the neck of an active volcano hardens, then a volcanic neck also known as volcanic plug gets created.
The volcanic plug thus formed offers more resistant to the flow of lava from the volcano and leads to a built up of pressure such that, the volcanic eruption can be extremely explosive in nature.
It is an example of Passive Transport because the process of Osmosis is where water molecules move from a region of higher water potential to a region of lower potential down a water potential gradient across a partially permeable membrane, little energy is required to carry out this process.
