Which plates are interacting in what ways?

Divergent Boundaries: When Plates Split Up

Imagine two plates deciding to go their separate ways. That’s a divergent boundary! As they pull apart, magma from deep within the Earth rises up to fill the gap, cools, and hardens, creating new crust. Think of it as the Earth constantly patching itself up. These boundaries are also known as constructive margins.

• Seafloor Spreading: This is where the magic happens in the oceans. Divergent boundaries create mid-ocean ridges, like the Mid-Atlantic Ridge – giant underwater mountain ranges where new oceanic crust is constantly being born. It’s like a massive underwater conveyor belt, pushing the seafloor outwards. The spreading rate varies, with fast-spreading ridges widening at over 90 mm/year, intermediate ridges at 40-90 mm/year, and slow-spreading ridges at less than 40 mm/year.
• Continental Rifting: Sometimes, this splitting action happens on land. When a continent starts to pull apart, it forms a rift valley. The East African Rift System is a fantastic example – a huge crack in the Earth’s surface where Africa is slowly breaking apart. If this rifting continues long enough, the continent could eventually split completely, forming a new ocean basin, just like the Red Sea did millions of years ago.

Convergent Boundaries: Collision Course!

Now, picture the opposite: plates crashing head-on. That’s a convergent boundary, also known as destructive boundaries. What happens next depends on what kind of plates are involved.

• Oceanic-Continental Convergence: When an oceanic plate (denser and heavier) meets a continental plate (lighter), the oceanic plate gets forced underneath in a process called subduction. This creates a subduction zone, marked by a deep trench in the ocean and a chain of volcanoes on the continent. The Andes Mountains in South America are a prime example, formed by the Nazca Plate diving under the South American Plate. The Cascade Range in the Pacific Northwest of the US, with iconic volcanoes like Mount St. Helens, are another example.
• Oceanic-Oceanic Convergence: When two oceanic plates collide, it’s a similar story. The older, denser plate subducts beneath the younger one, creating a trench and a volcanic island arc. Think of the Mariana Islands in the Pacific, home to the deepest point on Earth, the Mariana Trench.
• Continental-Continental Convergence: This is where things get really messy. When two continental plates collide, neither one wants to sink! Instead, they crumple and fold, creating massive mountain ranges. The Himalayas, the tallest mountains on Earth, were formed by the collision of India and Asia. The Alps, stretching across Europe, are another example of this colossal collision.

Transform Boundaries: Sliding Sideways

Finally, we have transform boundaries, where plates slide past each other horizontally. No new crust is created or destroyed here; these are conservative boundaries. But don’t let that fool you – they can still be pretty dramatic!

• Strike-Slip Faults: The most famous example is the San Andreas Fault in California. The Pacific Plate is grinding past the North American Plate, and this constant friction builds up stress. When that stress is released, BAM! Earthquake. The average slip rate along the San Andreas Fault is around 20 to 35 mm per year. Other examples include major faults in Pakistan, Turkey and along the Jordan River/Dead Sea.