Constructive Plate Boundaries and Ocean Ridges
Picture the seafloor splitting apart like a giant zip being undone - that's what happens at constructive plate boundaries. When tectonic plates diverge (pull apart), the pressure underneath drops dramatically, allowing hot magma to rise up through convection currents in the mantle.
As this magma erupts on the seafloor, it cools instantly in the cold ocean water, forming brand new rock. Over thousands of years, these continuous eruptions build up massive underwater mountain chains called ocean ridges - think of them as the Himalayas of the sea!
Rift valleys work in exactly the same way, but they form on land instead of underwater. The key difference is that rift valleys occur in continental crust rather than oceanic crust. Iceland sits right on top of one of these constructive boundaries, which explains why it's so volcanically active.
Quick Fact: The Mid-Atlantic Ridge is slowly pushing Europe and America further apart by about 2.5cm every year - roughly the same rate your fingernails grow!
