Earthquakes Earthquakes at a Plate Boundary. Tectonic Plates and Plate Boundaries. Plate Collision in NZ. Stuck Plate Boundary. Slow Slip Events. New Zealands Largest Fault. Earthquakes and Faults. New Zealand Earthquakes. Major Faults in New Zealand. The type of convergence -- called by some a very slow "collision" -- that takes place between plates depends on the kind of lithosphere involved.
Convergence can occur between an oceanic and a largely continental plate, or between two largely oceanic plates, or between two largely continental plates.
If by magic we could pull a plug and drain the Pacific Ocean, we would see a most amazing sight -- a number of long narrow, curving trenches thousands of kilometers long and 8 to 10 km deep cutting into the ocean floor. Trenches are the deepest parts of the ocean floor and are created by subduction. Off the coast of South America along the Peru-Chile trench, the oceanic Nazca Plate is pushing into and being subducted under the continental part of the South American Plate.
In turn, the overriding South American Plate is being lifted up, creating the towering Andes mountains, the backbone of the continent.
Strong, destructive earthquakes and the rapid uplift of mountain ranges are common in this region. Even though the Nazca Plate as a whole is sinking smoothly and continuously into the trench, the deepest part of the subducting plate breaks into smaller pieces that become locked in place for long periods of time before suddenly moving to generate large earthquakes.
Such earthquakes are often accompanied by uplift of the land by as much as a few meters. On 9 June , a magnitude This earthquake, within the subduction zone between the Nazca Plate and the South American Plate, was one of deepest and largest subduction earthquakes recorded in South America. Fortunately, even though this powerful earthquake was felt as far away as Minnesota and Toronto, Canada, it caused no major damage because of its great depth.
Oceanic-continental convergence also sustains many of the Earth's active volcanoes, such as those in the Andes and the Cascade Range in the Pacific Northwest. The eruptive activity is clearly associated with subduction, but scientists vigorously debate the possible sources of magma: Is magma generated by the partial melting of the subducted oceanic slab, or the overlying continental lithosphere, or both?
As with oceanic-continental convergence, when two oceanic plates converge, one is usually subducted under the other, and in the process a trench is formed. The Marianas Trench paralleling the Mariana Islands , for example, marks where the fast-moving Pacific Plate converges against the slower moving Philippine Plate. The Challenger Deep, at the southern end of the Marianas Trench, plunges deeper into the Earth's interior nearly 11, m than Mount Everest, the world's tallest mountain, rises above sea level about 8, m.
Subduction processes in oceanic-oceanic plate convergence also result in the formation of volcanoes. Over millions of years, the erupted lava and volcanic debris pile up on the ocean floor until a submarine volcano rises above sea level to form an island volcano. Such volcanoes are typically strung out in chains called island arcs. As the name implies, volcanic island arcs, which closely parallel the trenches, are generally curved. The trenches are the key to understanding how island arcs such as the Marianas and the Aleutian Islands have formed and why they experience numerous strong earthquakes.
The descending plate also provides a source of stress as the two plates interact, leading to frequent moderate to strong earthquakes. The Himalayan mountain range dramatically demonstrates one of the most visible and spectacular consequences of plate tectonics.
When two continents meet head-on, neither is subducted because the continental rocks are relatively light and, like two colliding icebergs, resist downward motion. Think about it and compare your idea to my sketch and a captioned version. Skip to main content. Faults Print In the articles you just read, the authors assume you know something about faults: how they are classified, what kind of motion they experience, what sense of stress they feel, and how to recognize them on a map.
Fault categories The sense of stress determines the type of fault that forms, and we usually categorize that sense of stress in three different ways: compression, tension, and shear. Handily, these three senses of stress also correlate with the three types of plate boundaries. Compressive stress happens at convergent plate boundaries where two plates move toward each other.
Tensional stress happens at divergent plate boundaries where two plates are moving away from each other. Shear stress is experienced at transform boundaries where two plates are sliding past each other. Artist's cross section illustrating the main types of plate boundaries.
Vigil from This Dynamic Planet—a wall map produced jointly by the U. Geological Survey, the Smithsonian Institution, and the U. Naval Research Laboratory. Fault symbol ID check! Based on a map prepared by the U. Rocks that line the boundary are pulverized as the plates grind along, creating a linear fault valley or undersea canyon. Earthquakes are common along these faults. In contrast to convergent and divergent boundaries, crust is cracked and broken at transform margins, but is not created or destroyed.
Virgin Islands. Home Ocean Exploration Facts What are the different types of plate tectonic boundaries?
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