What does a volcanic eruption depend on? a. It depends on the amount of air pressure around the volcano. b. It depends on the amount of past action from the volcano. c. It depends on the pressure of the magma against the surface above it. d. It depends on how many years it has been since it last erupted.

A volcanic eruption primarily depends on several factors, but the most critical one among the options provided is: **c. It depends on the pressure of the magma against the surface above it.** Here's a brief explanation of why this is the most relevant factor: - **Pressure of the magma (Option c)**: As magma rises towards the surface, it can build up pressure. When this pressure exceeds the strength of the rocks above, it can lead to an eruption. The composition of the magma (such as its viscosity and gas content) also plays a significant role in how explosive the eruption will be. The other options, while they may have some relevance, are not as directly linked to the mechanics of volcanic eruptions: - **a. Amount of air pressure**: While atmospheric pressure can have some effect, it is not a primary factor in determining whether a volcano will erupt. - **b. Amount of past action**: The history of a volcano can provide insights into its behavior, but it does not directly influence the occurrence of an eruption. - **d. Time since last eruption**: While the time since the last eruption can indicate the likelihood of future activity, it does not directly cause an eruption. In summary, the most critical factor influencing a volcanic eruption is the pressure of the magma against the surface above it.