What makes volcanoes erupt?
Volcanoes erupt due to a combination of geological processes involving magma, gas, and pressure. The primary reason for a volcanic eruption is the buildup of pressure from gas bubbles within magma, which is molten rock located beneath the Earth's surface. As magma rises through the crust, it can contain dissolved gases that expand as the pressure decreases. This process is akin to shaking a soda can; when the can is opened, the pressure is released, causing the soda to erupt out. Similarly, when the pressure from gas in magma becomes too great, it forces the magma to escape through weak points in the Earth's crust, resulting in an eruption.
The nature of a volcanic eruption—whether it is explosive or effusive—depends largely on the viscosity of the magma. If the magma is thick and viscous, it can trap gases, leading to a build up of pressure that results in explosive eruptions. These eruptions can send ash, rocks, and gases high into the atmosphere and create pyroclastic flows that are extremely dangerous. In contrast, if the magma is less viscous, gases can escape more easily, resulting in a gentler flow of lava down the volcano's slopes.
Volcanic eruptions are also influenced by tectonic activity. Most volcanoes are found at the boundaries of tectonic plates where one plate may subduct beneath another, causing melting and forming magma. This magma can accumulate in chambers beneath the surface until it finds a path to erupt. Hotspot volcanoes, like those in Hawaii, form away from plate boundaries where magma rises directly from deep within the Earth.
In summary, volcanoes blow their tops primarily due to gas build-up within molten rock (magma) that creates pressure. When this pressure exceeds the strength of surrounding rock formations, it leads to various types of eruptions that can have significant geological and environmental impacts.
