Not everyone can find a fascinating story about the formation and further existence of a portion of the earth's crust, but only if it does not go about the Pacific plate. Having arisen on the site of the ancient disappeared ocean Pantalassa, 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 capable of captivating anyone with its history.
How did the Pacific plate
It is believed that just over 440 million years ago, the Pantalassa Ocean existed, which occupied almost half the entire surface area of the globe. Its waves were washed by the only supercontinent on the planet called Pangea.
Such large-scale phenomena launched a number of processes, as a result of which three lithospheric plates located under the abyss of the ancient ocean converged in a circular motion, after which a fault appeared. A molten substance gushed out from the plastic asthenosphere through it, forming at that time a tiny block of the earth's crust of the oceanic type. This event occurred in the Mesozoic era, about 190 million years ago, presumably in the area of modern Costa Rica.
The Pacific Plate is now under almost the entire ocean of the same name and is the largest on Earth. It grew gradually due to spreading, i.e., build-up by mantle material. It also replaced the blocks surrounding it, decreasing by subduction. By subduction, we understand the movement of oceanic plates as continental, accompanied by their destruction and going to the center of the planet along the edges.
What is the unique part of the lithosphere under the Pacific Ocean
In addition to the dimensions by which the Pacific plate significantly exceeds all other separate lithospheric areas, it differs in composition, being the only completely composed of the oceanic type crust. All other similar elements of the earth's surface have a continental type of structure or combine it with the oceanic (heavier and denser).
It is here, in the western part, that the deepest of the places known on Earth is located - the Mariana Trench (otherwise - the gutter). Its depth cannot be called very accurately, but, according to the results of the last measurement, it is about 10,994 kilometers down from sea level. Its occurrence is the result of subduction that occurred during the collision of the Pacific and Philippine plates. The first of them, as older and heavier, plunged below the second.
At the borders of the Pacific Plate with others forming the bottom of the ocean, the edges of the participants in the collision are growing. They move apart relative to each other. Due to this, the plates located in the vicinity of the continental blocks are subjected to constant subduction.
In these zones is the so-called Ring of Fire - the region of the highest seismic activity on Earth. There are 328 of 540 active volcanoes known on the planet's surface. It is in the zone of the Ring of Fire 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 hot spot responsible for the formation of the Hawaiian Islands, in whose honor it is named. A whole chain of more than 120 cooled and, to varying degrees, destroyed volcanoes, as well as four active ones.
It is believed that the movement of the block of the earth's crust is not the cause of their appearance, but, on the contrary, a consequence. The mantle plume - a hot stream in the direction from the core to the surface - changed its movement and manifested itself in the form of volcanoes sequentially 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 opinion that the hot spot has a constant focus, and the bending of volcanic ridges of different ages that make up the Hawaiian arc, generated the movement of the plate relative to it.
Pacific bottom movement
All lithospheric blocks are constantly moving, and the speed of this movement is different, as is the direction. Some plates tend to meet each other, others move apart, and others move in parallel in one or different directions. 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 a dozen million years.
Together with the indicators of other blocks, these figures increase. For example, with the Nazca plate, on the border of which a part of the Fiery belt is located, the Pacific plate is moved 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 becoming smaller, since diving of the plates of its bottom under the continental in the areas of collision leads to a reduction in the first, sunken by the edges in the asthenosphere during subduction.