Mountain Maker, Earth Shaker
Intro
Build mountains. Trigger volcanoes. Create new sea floor. Use this interactive landscape to explore four types of plate tectonic activity. Red lines on the map show you where each type of activity takes place on Earth.
Instructions:
Click and drag the arrows on the four plates to move them. You can only move each plate in the direction of its arrow.
Divergent Boundary
A divergent (or spreading) boundary occurs where two plates move apart. Magma, or molten rock, rises from Earth's interior to fill the gap.
Earth's longest mountain range is an underwater chain 40,000 miles (65,000 km) long. It runs down the middle of the Atlantic Ocean (surfacing at Iceland), around Africa, through the Indian Ocean, between Australia and Antarctica, and north through the Pacific Ocean. Along the top of this ocean ridge is a deep crack, called a rift valley. Here, magma wells up from Earth's interior. Cooled by the sea, it solidifies into rock, creating new ocean floor.
In the North Atlantic ridge, 0.75 inches (2 cm) of new floor is created each year. In the East Pacific rise, the rate is 12.5 inches (32 cm) per year.
Convergent Boundary (Oceanic-Continental)
When two plates push together, a convergent boundary occurs. Land masses are less dense than the ocean floor, so when an oceanic plate and a continental plate collide, the oceanic plate slides, or subducts, under the continental plate, bending downward to great depths.
The oceanic plate carries along water as it descends into the mantle. At the high temperature and pressure of the depths additional water is released from the oceanic plate. This causes the rock of the mantle to melt, forming magma that can produce volcanoes.
Sea-floor spreading at divergent boundaries continually pushes out new crust. But Earth isn't getting any bigger. Ocean-floor melting at convergent boundaries keeps Earth the same size.
Convergent Boundary (Continental-Continental)
When two continental plates push together, the land masses resist subduction because they are of similar density. The crust crumples and folds, pushing mountains and plateaus upward.
The Himalayas, the highest mountains in the world, are still being created in this way, as the Indian plate slides northward under the Eurasian plate. The European Alps and the original Appalachians were formed this way as well. The tectonic forces that created the Appalachians ceased long ago—all that's left are the eroded remnants of a once giant mountain range.
Transform Boundary
A transform boundary occurs where two plates slide against each other. The plates do not slide smoothly, but build up tension and then release it with a burst of movement, which is felt as an earthquake.
The San Andreas Fault is a widely studied transform boundary. To the west is the Pacific plate, moving northwest. To the east is the North American plate, moving southeast.
Los Angeles, located on the Pacific plate, is now 340 miles (517 km) south of San Francisco, located on the North American plate. In 16 million years, the plates will have moved so far that Los Angeles will be north of San Francisco!