lesson 6/7: plate boundaries Flashcards
transform
when the plates slide past each other. These plates get caught, and with a sudden burst of energy, slide past each other very quickly. Earthquakes are caused by the plates passing each other, creating friction, and pressure building then a release. Transform fault (a fracture in the rock). For example, the San Andreas Fault located in California. 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!
convergent type 1
1 Oceanic- continental plates. The continental plate is less dense, meaning that the oceanic plate is forced underneath the continental plate. This creates a subduction zone. This causes trenches, volcanoes, subduction zones, and even volcanic eruptions. For example, The west coast of South America, near Chile. Large mountain range located here, filled with volcanoes.
convergent type 2
oceanic-oceanic plates. The less dense plate slips (and normally the older plate) slip underneath the denser plate causing subduction zones, trenches, underwater volcanoes, and islands. An example of a convergent type 2 boundary is the Mariana trench.
convergent type 3
continental-continental plates . These plates get folded and pushed upwards, creating mountains. Mountains and mountain ranges formed at boundary. This causes megathrust earthquakes and tsunamis. For example, the Himalayas, located in Nepal.
divergent type 1
oceanic-oceanic plates, these cause a rift, or gap/opening in the sea floor. Magma rises into the gap between the plates, creating a sea floor spread, and new crust. This causes ridges, rifts, and mic-ocean ridges. For example, the Mid-Atlantic ridge located in the Atlantic ocean.
divergent type 2
Continental - continental plates. They are thicker, and denser. Water may flow into the space between these plates, possible creating a new ocean. This causes rift valleys. Water can flow into these valleys, creating oceans, for example the Atlantic Ocean.
convergent plate boundary
the plates are coming together. These boundaries are also called destructive boundaries as some of the crust gets destroyed. The rock gets broken down, and crust is destroyed. When two plates push together, a convergent boundary occurs. The plate on either side of the boundary may be continental or oceanic. At an oceanic-continental boundary (shown in the diagram), an oceanic plate and a continental plate collide. Land masses are less dense than the ocean floor, so 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 mantle rock to melt, forming magma that can produce volcanoes. When two continental plates collide, the land masses resist subduction because the crustal rocks are of similar density. The crust crumples and folds, pushing mountains and plateaus upward. The Himalayas in Asia, the highest mountains in the world, are still being created in this way, as the Indian plate continues to push into the Eurasian plate. When two oceanic plates collide, the denser plate subducts.
divergent plate boundary
The plates move away from each other. Also known as constructive plate boundaries as the magma is rising up causing sea-floor spreading and the creation of new crust on the earth’s surface. A divergent boundary (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 volcanic chain 40,000 miles (65,000 km) long. Called the mid-ocean ridge, it runs down the middle of the Atlantic Ocean (surfacing in 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. The mid-ocean ridge is where plates are moving apart—and therefore creating new sea floor—at a rate of about 1 inch (2.5 cm) per year. In the East Pacific Rise, the rate can be as high as 6 inches (15 cm) per year. Sea-floor spreading at divergent boundaries continually pushes out new crust. But because of the subduction of oceanic crust at convergent boundaries, the size of Earth remains the same.
