The Pacific Plate is the largest and most unusual of the lithospheric blocks

2024 Author: Henry Conors | [email protected]. Last modified: 2024-02-12 02:42

Not everyone can find a fascinating story about the formation and further existence of a section of the earth's crust, but only if it is not about the Pacific plate. Emerging on the site of the ancient disappeared ocean, Panthalassa, which has become the largest on the planet, unique in composition and inextricably linked with such natural phenomena as the Mariana Trench, the Pacific Ring of Fire and the Hawaiian hot spot, it is able to fascinate anyone with its history.

How the Pacific Plate appeared

It is believed that just over 440 million years ago there was an ocean of Panthalassa, which occupied almost half of the entire surface area of the globe. Its waves washed over the only supercontinent on the planet called Pangea.

Such large-scale phenomena launched a series of processes, as a result of which the three under the abyssof the ancient ocean, the lithospheric plates converged in a circular motion, after which a fault appeared. Molten matter gushed through it from the plastic asthenosphere, forming a tiny block of the earth's crust of the oceanic type at that time. This event took place in the Mesozoic era, about 190 million years ago, presumably in the area of modern Costa Rica.

The Pacific Plate is now located under almost the entire ocean of the same name and is the largest on Earth. It grew gradually due to spreading, i.e., buildup by mantle matter. It also replaced the surrounding blocks that were decreasing by subduction. Subduction is understood as the movement of oceanic plates under the continental ones, accompanied by their destruction and departure to the center of the planet along the edges.

What is unique about the area of the lithosphere under the Pacific Ocean

In addition to the dimensions, in which the Pacific Plate significantly exceeds all other individual lithospheric areas, it differs in composition, being the only one completely composed of oceanic-type crust. All other similar elements of the earth's surface have a continental type of structure or combine it with an oceanic (heavier and denser) type.

It is here, in the western part, that the deepest known place on Earth is located - the Mariana Trench (otherwise - the trench). Its depth cannot be given with extreme accuracy, but, according to the results of the last measurement, it is about 10,994 kilometers below sea level. Its occurrence is the result of subduction that occurred during the collisionPacific and Philippine plates. The first of them, being older and heavier, sank below the second.

On the borders of the Pacific plate with others that form the ocean floor, the edges of the collision participants are growing. They move apart relative to each other. Due to this, plates adjacent to continental blocks are subject to constant subduction.

In these zones is the so-called Ring of Fire - the region of the highest seismic activity on Earth. Here are 328 of the 540 active volcanoes known on the surface of the planet. It is in the Ring of Fire zone that earthquakes most often occur - 90% of the total and 80% of the most powerful of all.

In the northern region of the Pacific Plate there is a hotspot responsible for the formation of the Hawaiian Islands, after which it is named. A whole chain of more than 120 cooled down and destroyed volcanoes to varying degrees, as well as four active ones.

It is believed that the movement of a block of the earth's crust is not the cause of their appearance, but, on the contrary, a consequence. The mantle plume - a hot flow in the direction from the core to the surface - changed its movement and manifested itself in the form of volcanoes successively located along this path, and also set the direction of the plate. All this formed underwater ridges and an island arc.

Although there is an alternative view that the hotspot has a constant direction, and the bending of volcanic ridges of different ages that make up the Hawaiian arc, gave rise to the movement of the plate relative to it.

Pacific floor movement

All lithospheric blocks are constantly moving, and the speed of this movement is different, as well as the direction. Some plates tend to meet each other, others move apart, others move in parallel in one or different directions. The speed varies from a few millimeters to tens of centimeters per year.

The Pacific Plate is moving quite actively. Its speed is about 5.5-6 cm/year. Scientists have calculated that at this speed, Los Angeles and San Francisco will "come together" in about ten million years.

Together with the indicators of other blocks, these figures are increasing. For example, with the Nazca plate, on the border of which part of the Fire Belt is located, the Pacific plate is moving apart by 17 centimeters annually.

How the Pacific is changing

Despite the increase in the area of the largest plate, the size of the Pacific Ocean is getting smaller, as the subduction of its bottom plates under the continental ones in areas of collision leads to a reduction in the former, sinking edges into the asthenosphere in the process of subduction.