Why do convergent plates move

Vincent and the Grenadines are examples of islands formed through this type of plate boundary. Visit the Interactive Plate Boundary Map to explore satellite images of these three areas. Effects that are found at this type of plate boundary include: a zone of progressively deeper earthquakes; an oceanic trench; a chain of volcanic islands; the destruction of oceanic lithosphere. This is a difficult boundary to draw.

First it is complex and second, it is poorly understood when compared to the other types of plate boundaries. In this type of convergent boundary, a powerful collision occurs. The two thick continental plates collide, and both of them have a density that is much lower than the mantle, which prevents subduction there may be a small amount of subduction, or the heavier lithosphere below the continental crust might break free from the crust and subduct. Fragments of crust or continent margin sediments might be caught in the collision zone between the continents, forming a highly deformed melange of rock.

The intense compression can also cause extensive folding and faulting of rocks within the two colliding plates. This deformation can extend hundreds of miles into the plate interior. The Himalaya Mountain Range is the best active example of this type of plate boundary. Visit the Interactive Plate Boundary Map to explore satellite images of the Himalaya Range where the Indian and Eurasian plates are currently in collision.

The Appalachian Mountain Range is an ancient example of this collision type and is also marked on the map. Effects found at a convergent boundary between continental plates include: intense folding and faulting; a broad folded mountain range; shallow earthquake activity; shortening and thickening of the plates within the collision zone. Contributor: Hobart King Publisher, Geology. What is the San Andreas Fault? How did the Hawaiian Islands Form? Find Other Topics on Geology. Maps Volcanoes World Maps.

Teaching Plate Tectonics. Earth's Internal Structure. Divergent Boundary. When oceanic plates are subducted, they often bend, resulting in the formation of oceanic trenches. These often run parallel to volcanic arcs and extend deep beneath the surrounding terrain.

The deepest oceanic trench, the Mariana Trench , is more than 35, feet below sea level. It is the result of the Pacific Plate moving beneath the Mariana Plate. When oceanic and continental plates collide, the oceanic plate undergoes subduction and volcanic arcs arise on land.

These volcanoes release lava with chemical traces of the continental crust they rise through. Oceanic plates are denser than continental plates, which means they have a higher subduction potential. They are constantly being pulled into the mantle, where they are melted and recycled into new magma. The oldest oceanic plates are also the coldest, as they have moved away from heat sources such as divergent boundaries and hot spots.

This makes them denser and more likely to subduct. Continental-continental convergent boundaries pit large slabs of crust against each other. This results in very little subduction, as most of the rock is too light to be carried very far down into the dense mantle. Instead, the continental crust at these convergent boundaries gets folded, faulted, and thickened, forming great mountain chains of uplifted rock.

Magma cannot penetrate this thick crust; instead, it cools intrusively and forms granite. Highly metamorphosed rock, like gneiss, is also common.

The Himalayas and the Tibetan Plateau , the result of 50 million years of collision between the Indian and Eurasian plates, are the most spectacular manifestation of this type of boundary. The jagged peaks of the Himalayas are the highest in the world, with Mount Everest reaching 29, feet and more than 35 other mountains exceeding 25, feet. The Tibetan Plateau, which encompasses approximately 1, square miles of land north of the Himalayas, averages around 15, feet in elevation.

Actively scan device characteristics for identification. Use precise geolocation data. Select personalised content. Create a personalised content profile. 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. Instead, the crust tends to buckle and be pushed upward or sideways. The collision of India into Asia 50 million years ago caused the Indian and Eurasian Plates to crumple up along the collision zone.

After the collision, the slow continuous convergence of these two plates over millions of years pushed up the Himalayas and the Tibetan Plateau to their present heights. Most of this growth occurred during the past 10 million years. The Himalayas, towering as high as 8, m above sea level, form the highest continental mountains in the world. Moreover, the neighboring Tibetan Plateau, at an average elevation of about 4, m, is higher than all the peaks in the Alps except for Mont Blanc and Monte Rosa, and is well above the summits of most mountains in the United States.

Below: Cartoon cross sections showing the meeting of these two plates before and after their collision. The reference points small squares show the amount of uplift of an imaginary point in the Earth's crust during this mountain-building process. The zone between two plates sliding horizontally past one another is called a transform-fault boundary, or simply a transform boundary. The concept of transform faults originated with Canadian geophysicist J. Tuzo Wilson, who proposed that these large faults or fracture zones connect two spreading centers divergent plate boundaries or, less commonly, trenches convergent plate boundaries.

Most transform faults are found on the ocean floor. They commonly offset the active spreading ridges, producing zig-zag plate margins, and are generally defined by shallow earthquakes. However, a few occur on land, for example the San Andreas fault zone in California. This transform fault connects the East Pacific Rise, a divergent boundary to the south, with the South Gorda -- Juan de Fuca -- Explorer Ridge, another divergent boundary to the north.

The Blanco, Mendocino, Murray, and Molokai fracture zones are some of the many fracture zones transform faults that scar the ocean floor and offset ridges see text. The San Andreas is one of the few transform faults exposed on land. The San Andreas fault zone, which is about 1, km long and in places tens of kilometers wide, slices through two thirds of the length of California.

Land on the west side of the fault zone on the Pacific Plate is moving in a northwesterly direction relative to the land on the east side of the fault zone on the North American Plate. Oceanic fracture zones are ocean-floor valleys that horizontally offset spreading ridges; some of these zones are hundreds to thousands of kilometers long and as much as 8 km deep. Examples of these large scars include the Clarion, Molokai, and Pioneer fracture zones in the Northeast Pacific off the coast of California and Mexico.

These zones are presently inactive, but the offsets of the patterns of magnetic striping provide evidence of their previous transform-fault activity. Not all plate boundaries are as simple as the main types discussed above. In some regions, the boundaries are not well defined because the plate-movement deformation occurring there extends over a broad belt called a plate-boundary zone.

One of these zones marks the Mediterranean-Alpine region between the Eurasian and African Plates, within which several smaller fragments of plates microplates have been recognized. Because plate-boundary zones involve at least two large plates and one or more microplates caught up between them, they tend to have complicated geological structures and earthquake patterns.

We can measure how fast tectonic plates are moving today, but how do scientists know what the rates of plate movement have been over geologic time? The oceans hold one of the key pieces to the puzzle. Because the ocean-floor magnetic striping records the flip-flops in the Earth's magnetic field, scientists, knowing the approximate duration of the reversal, can calculate the average rate of plate movement during a given time span.