Science Facts

What Happens When Continents Collide? – Geoscience

Continents Collision

Over 20 million years, the Farallon and Caribbean Plates’ shifting produced the Central America Volcanic Arc. As these plates surf the Earth’s magma layer far beneath the Pacific Ocean floor, the Caribbean Plate migrated eastward. About 15 million years ago, South America finally collided with this Central American Arc.

This gradually closed the water connection between the Pacific and the Caribbean, creating a land bridge, which connected North America to South America. Terrestrial organisms could now cross between the two continents. And from the fossil records, it’s evident that different waves of their dispersals took place. Even though plants don’t physically move, they are easily dispersed by wind and waves. So they migrated first, along with a few species of birds.

Some freshwater fishes and amphibians followed them. Finally, various mammals began to traverse the bridge. From South America, mammals like ground sloths and glyptodonts were widely distributed in North America. Moreover, many South American tropical mammals, like monkeys and bats, colonized the forests of Central America and are very abundant today.

What happens when continents collide?

Almost all the Earth’s landmass was clumped into one gigantic supercontinent called Pangea. The land was like one tightly knit bunch. The crust and upper part of the molten mantle are together called the lithosphere. These are broken up into several tectonic plates that fit together like puzzle pieces. These plates glide around on the Earth’s molten interior, creating mountains and volcanoes where they collide.

The plates only move centimeters each year, but sometimes dramatic events happen suddenly. For example, the giant crack that just opened up in Africa. In March of 2018, a huge crack appeared in Kenya. There are a few possible explanations, like heavy rain or underground water washing away sediment. But it’s also possible that Africa is splitting in two.

The same forces that cause the plates to move can also break them apart. It looks like the African plate is breaking up into unequal parts: the Somali and Nubian plates. Africa isn’t the only continent making a break for it. Australia is on the move too. In fact, the entire country is moving north so quickly that it could throw GPS systems off in just a few years.

Two continental plates collide

The Earth’s lithosphere is made up of dozens of tectonic plates. A complex network of moving pieces beneath the Earth that continue to shape our continents. Churning currents within the molten rocks below slide the plates in slow motion. They move only one to two inches a year, but even this can cause them to crash together or rip apart. These plate movements are the cause of much of the geological activity around the globe. Earthquakes, volcanoes are all a result of the power of plate tectonics. As the Pacific and Caribbean plates moved towards each other, pushing up the seafloor, two continents connected.

Continents structure
Continents structure

And a whole new chapter in the evolution of its inhabitants began. Here you see how life is closely related to the plate tectonics, to the continents moving. Without the collision of these two continents, the animals would never have been connected. Animals like the armadillo, porcupine, and opossum only exist in North America because their ancestors crossed this ancient land bridge. And it’s the same reason that South America has its horses. Plate tectonics will continue to change how our world looks. Not only the physical lands change but the land’s inhabitants as well.

South American predator marsupials went extinct 3 million years ago. At which point, North American predators, such as cats, bears, and foxes, migrated south and occupied the ecological space left behind. Horses, llamas, tapirs, cougars, saber-toothed cats, gomphotheres, and later humans headed south across the land bridge. But what happened on land is only half the story.

What had been one giant ocean was now two, creating differences in temperature and salinity for the two bodies of water. The isthmus also became a barrier for many marine organisms, like mollusks, crustaceans, foraminifera, bryozoans, fish, and separated the populations of many marine species. It also allowed the establishment of the thermohaline circulation, a global water conveyor belt. It transports warm water across the Atlantic and influences the East Coast of North America, the West Coast of Europe, and many other areas.

Effects of continent collision

According to Scotese’s estimates, it will smack into China, getting all up in its business and fusing within 65 million years. Meanwhile, the northern edge of Africa will have joined up with the southern edge of Europe, eliminating the mediterranean sea.

Around 100 million years from now, the Pacific ocean will start getting bigger as the Americas drift towards Europe, but not before Alaska nicks a Russian piece. And while all this is happening, Antarctica will start drifting into the Indian ocean. It will join Brazil and Madagascar at the southern tip of Africa while Newfoundland smooshes into the Ivory Coast. In 250 million years, we could be looking at a new supercontinent, Pangea Proxima.

Another one is North America crosses the arctic ocean to snuggle up to Russia, forming another supercontinent dubbed Amasia. It’s poetic that the whole gang could get back together again. The cycle will continue until the earth’s molten interior cools or something else causes the tectonic activity to stop.

In New Zealand, two tectonic plates collide. In the south, we have a trench. A trench means that one side, the Australian plate, goes down beneath the Pacific plate, about 200 kilometers deep. Along that plate boundary, there are many earthquakes. The plate collision is mostly taken up by movement across the Alpine Fault in the central South Island.

Much of the earthquake activity on the Alpine Fault is sideways movement and a little bit of upward movement. The upward movement is the thing that causes the very strong boundary between Westland and the high peaks of the Southern Alps. Away from the Alpine Fault, it is the main fault of the plate boundary. There are many smaller faults, such as those that generated the devastating earthquakes in Canterbury.

In the North, the Alpine Fault breaks up into a series of faults, and these are known as the Marlborough fault system. Most of the movement transitions onto the Hope Fault and heads out towards this plate boundary to the north. The North Island situation is more or less the opposite of what’s occurring in Fiordland. The Pacific plate is now going down underneath the North Island, which is still part of this great big Australian plate. And it dives down to five and six hundred kilometers deep.

As well as the Master Fault is Subduction Fault, the North Island’s broken up into many smaller parts. So the earthquake activity is quite varied in the North Island. There is the possibility of massive earthquakes on the plate interface, on the East Coast North Island subduction zone. And that could be similar to big earthquakes that have occurred in Japan or Indonesia. Earthquakes are generally more minor on these faults. The Edgecumbe quake of 1987 is a typical example of the earthquakes that we expect to be associated with the volcanic zone.


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Sources:

Ernst, W.G., “Preservation/exhumation of ultrahigh-pressure subduction complexes”.
Ernst, W.G.; Maruyama, S. Wallis; Wallis, “Buoyancy-driven, rapid exhumation of ultrahigh-pressure metamorphosed continental crust.” Proceedings of the National Academy of Sciences. 94 (18): 9532–9537.
O’Brien, P.J. (2001). “Subduction followed by collision; Alpine and Himalayan examples.” Physics of the Earth and Planetary Interiors.
Toussaint, G.; “Tectonic evolution of a continental collision zone: A thermomechanical numerical model.”

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