Volcanoes: Magma Rising
More than a century ago, the city of Saint-Pierre was known as the Paris of the Caribbean. Located on the island of Martinique, Saint-Pierre was a center of trade in rum, sugar, cocoa, and coffee. Its boulevards were lined with beautiful homes and shops.
But in the spring of 1902, all of that changed…
How does subduction cause volcanoes to form?
- When an oceanic plate collides with a continental plate, it sinks into the mantle below.
- As the oceanic plate sinks, fluid (shown in purple) is squeezed out of it.
- The fluid flows up into the mantle rock above and changes its chemistry, causing it to melt. This forms magma (molten rock).
- The magma rises and collects in chambers within the crust.
- As magma fills the chamber, pressure grows. If the pressure gets high enough, the magma can break through the crust and spew out in a volcanic eruption. Most explosive volcanoes occur above subduction zones.