Japan was formed by convergent oceanic plates.
The study of plate tectonics encompasses three kinds of plate boundaries that move on the Earth’s surface to create its geologic features: divergent, convergent and transform boundaries. Divergent plates are those which are moving away from each other, while convergent are moving towards one another. Transform plates move horizontally against each other. These plates and their boundaries exhibit different characteristics which contribute to the way they shape the planet.
Divergent Plates – Oceanic
The boundary of divergent plates under the ocean’s lithosphere produces a mid-ocean ridge. This is due to the convection currents lifting the lithosphere which then stretches and produces a fissure. Magma from the mantle, located below the lithosphere, flows into the fissure and solidifies. Characteristics of the boundary between divergent plates is a mid-ocean ridge — such as the Mid-Atlantic Ridge; volcanic fissure eruptions and creation of new seafloor; and widening of the ocean basin.
Convergent Plates – Oceanic
Subduction occurs when convergent plates meet under the ocean, with one plate moving below the other. As the subducted plate is forced deeper into the Earth it heats and melts. The resulting magma forces its way upwards through the overlying rock and forms a volcanic eruption cone when it reaches the surface. These cones start deep under the ocean; with time they grow to be higher than sea level, thus forming an island chain such as in Japan and the Aleutian Islands. Deep oceanic trenches are also formed along the convergent plate boundaries.
Divergent Plates – Continental
The Red Sea in the Middle East was formed by diverging continental plates.
The thick continental plates exhibit different behavior when located above a divergent plate boundary. The plate is arched upwards and pulled thin causing a fracture that produces a rift-shaped structure. Faults develop on both sides of the rift as the plates pull apart, the central portion slides downwards and earthquakes occur. Fresh water streams and rivers will flow into the rift forming a long narrow lake; if the rift becomes deep enough ocean waters can flow in creating a long narrow sea. The Red Sea is a prime example of a deep rift that has become a sea. In its early stages of development, the East Africa Rift has several lakes and is still above sea level.
Convergent Plates – Continental
The Himalaya Mountains are still being formed by convergent continental plates.
Convergent boundaries between continental plates subject both plates to a powerful collision as neither plate is subducted due to their lower density in relation to the mantle. Compression of the rock in both plates results in intense folding and the creation of many faults. Often broad folded mountain ranges are formed. The Appalachian Mountains are an example of an ancient plate collision. The Indian and Eurasian plate are now colliding and forming the Himalayas.
Convergent Plates – Continental and Oceanic
Collisions between continental and oceanic plates result in the denser and thinner ocean plate being subducted. As the plate is forced deeper into the mantle, it melts and forms magma. A zone of earthquake activity forms and possibly an ocean trench forms directly offshore of the continent. Volcanic eruptions a few hundred miles inland are also evident. Examples of this type of convergent boundary include the Andes Mountains in South America and the Washington-Oregon coastline of the United States.