Convergent Boundaries

Introduction
Convergent boundaries form when two crustal plates are colliding. The plates form a subduction zone with one plate descending beneath the other plate. One of the converging plates must be an oceanic plate to form a subduction zone. When two continental plates collide mountain ranges like the Himalayas form.

Trenches at Convergent Boundaries, USGS

Trenches form at subduction zones, USGS

Subduction zone
The subducting plate is being recycled as it begins to melt at about 100 kilometers. The water soaked oceanic plate forms molten rock that collects in magma chambers.

Buoyant molten rock
The molten rock is buoyant because it is hotter and less dense than the surrounding rocks. The rocks move up through the overlying rocks to erupt at volcanic vents forming an arc of volcanoes on the continental side of the subduction zone.

Island arcs form at convergent Boundaries, USGS

Subduction zone, USGS

Causes a megathrust earthquake
Converging plates in subduction zones often become locked. Pressure builds in the rocks until they fracture. If the break is along hundreds of kilometers of fault line a megathrust earthquake occurs.

Causes of tsunami waves
The breaking rocks allow the overriding plate to slip over part of the subducting plate all along the fault line. The plate movement on the ocean floor can cause a tsunami. The 2004 Indian Ocean tsunami was triggered by a megathrust earthquake at a convergent boundary.

More Pacific Ring of Fire Links

Mt. Spurr Find out more about Mt. Spurr which is the tallest peak in the Aleutian Volcanic Arc.

Challenger Deep Learn more about the deepest point on the ocean floor that lies seven miles beneath the ocean's surface.

Composite Volcano Learn more about these towering mountains that form on the continents near subduction zones.

Cascadia Subduction Zone Learn more about the Cascadia Subduction Zone in the Pacific Northwest where a great earthquake could occur at any time.


2010 Chilean Earthquake Another megathrust earthquake struck Chile in 2010. Find out why these earthquakes occur so frequently there.

Island Arcs  Island arcs are a string of volcanic islands in the ocean. Find out more about these islands in the Pacific Ocean.

Convergent Boundaries Learn how these boundaries have created the Ring of Fire in the Pacific Ocean.

Pacific Ring of Fire Learn more about the Ring of Fire which is home to towering volcanoes and great earthquakes.

Kids Fun Science The links on our home page include information about volcanoes, science activities, plate tectonics, the rock cycle and much more.