Subduction Zone Meaning
Let’s briefly understand what a subduction zone is. A subduction zone is perhaps the greatest crash scene on Earth. These boundaries mark the strike between two of the planet's tectonic plates. The plates are pieces of crust which gradually move across the planet's surface over millions of years. Where two tectonic plates collide at a subduction zone, one bends and slides below the other, curving down into the mantle (the hotter layer beneath the crust). Subduction zones are massive boundaries, thus they produce very large and impactful earthquakes.
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Amazing Events in Subduction Zones
The Earth’s couple of tectonic plates can be millions of miles across and underlie both oceans and continents. These plates slam into, slide past, and move apart from each other. Where they slam and one plate is thrust underneath another (a subduction zone), the most impactful earthquakes, landslides, tsunamis, and volcanic eruptions arise.
Events in Subduction Zones
Following are the Events That Take Place in Subduction Zones -
Earthquakes
Cramming two gigantic slices of Earth's crust together is like stroking two pieces of sandpaper against each other. The gigantic scale of subduction zones implies they can induce cosmic earthquakes. The biggest earthquakes ever documented were on subduction zones, recording a magnitude of 9.5 in Chile (1960) and a magnitude of 9.2 in Alaska (1964).
Tsunamis
Subduction zones are generally formed along coastlines, so tsunamis tend to always produce close to where people live. "There's a silver lining there.”If these earthquakes occur beneath a city, the city would just have no chance. But unfortunately, sometimes a tsunami is produced."
When a subduction zone earthquake strikes, Earth's crust bends and breaks like a freed spring. For earthquakes bigger than a magnitude 7.5, this can bring about a tsunami, a colossal sea wave, by abruptly moving the seafloor. However, not all subduction zone earthquakes will give rise to tsunamis. Also, some earthquakes activate tsunamis by sparking underwater landslides.
Whatever their cause, the tsunami from subduction zones may strike in minutes for coastal areas near an earthquake, or hours later, after the waves travel along the sea.
Volcanoes
As plate tectonics subduction zones slide into the mantle, the hotter layer underneath Earth's crust, the heating disperse fluids trapped in the plate. These fluids, such as carbon dioxide and sea water, can partially melt the overlying crust, producing magma. And magma (molten rock) often indicates volcanoes.
The Toba volcanic explosion in Indonesia, the biggest volcanic eruption in the past 25 million years, had been from a subduction zone volcano.
Abundant Landslides
Landslides are specifically profuse in subduction zones, where geologic mechanisms form steep rapidly evolving topography. Onshore, high rates of rainfall on the seaward side of the mountain chains formed by the compressing of the plates make landslides more likely. Offshore, thick sediments amass, constructing steep unstable slopes.
Land-Level Changes Over Massive Areas
In the hundreds of years between megathrust earthquakes, the compressing motions cause the upper plate to upsurge and uplift just above the locked region, over thousands of square kilometers. Almost spontaneously after a megathrust earthquake, the uplifted area drops by as much as a few meters (1 meter is about 3 feet), inducing sea level to rise by amounts that would take hundreds of years if because of climatic change.
Magma Generation in Subduction Zones
When the (literally very old) oceanic crust sinks back into the mantle in a subduction zone, it comes continuously under huge pressure and temperature. The rocks contain considerable amounts of carbon dioxide, water and other fluids which are released into the blanketed mantle wedge.
Magmas Change Composition
The magmas in subduction zone volcanoes are commonly explosive since they appear at the surface as very viscous (sticky) and gas-rich. Why?
On their way up to the surface, these magmas can (and essentially do) experience a variety of processes, such as cooling and crystallizing when they pool and cool in magma chambers at varying depths.
Fun Facts
Plate tectonics subduction zones can carry along both oceanic crust and continental crust, or they may be made of only either kind of crust.
Continental crust is less dense and condensed than the Oceanic crust.
At a subduction zone, the oceanic crust generally descends into the mantle underneath a lighter continental crust.
Scientists believe sometimes, the oceanic crust may grow so old and dense that it collapses and in a spur of a moment develops a subduction zone
With a similar type of crust collision, such as continent-continent, the plates may crash together without subducting and scrumple together like crashing cars.
The gigantic Himalaya mountain chain was created this way when India rammed into Asia.
FAQs on Subduction Zone
1. What is a subduction zone in simple terms?
A subduction zone is a place on Earth where two tectonic plates collide, and one plate is forced to slide underneath the other into the mantle. This typically happens because the subducting plate, usually an oceanic plate, is denser than the plate it is moving under, which can be either a continental plate or another oceanic plate.
2. What are the main types of subduction zones?
There are two primary types of subduction zones, distinguished by the kinds of tectonic plates involved:
- Oceanic-Continental: This occurs when a dense oceanic plate subducts beneath a less dense continental plate. This process often forms a volcanic mountain range on the continent, like the Andes Mountains.
- Oceanic-Oceanic: This happens when one oceanic plate subducts under another. This creates a deep-sea trench and a chain of volcanic islands known as an island arc, such as Japan or the Aleutian Islands.
3. Where can we find examples of subduction zones on Earth?
Subduction zones are found all around the world, most famously along the edges of the Pacific Ocean in an area called the Ring of Fire. Key examples include the coast of South America, where the Nazca Plate subducts under the South American Plate, and the region around Japan, where the Pacific Plate subducts under plates to the west.
4. How is a subduction zone related to a convergent plate boundary?
A subduction zone is a specific type of convergent boundary. A convergent boundary is any location where two tectonic plates are moving toward each other. Subduction is the geological process that occurs at these boundaries when one of the plates is dense enough to sink below the other. Not all convergent boundaries are subduction zones; for example, when two continental plates collide, they tend to crumple and form large mountain ranges like the Himalayas.
5. Why do the world's largest earthquakes happen at subduction zones?
The largest earthquakes, known as megathrust earthquakes, occur at subduction zones because of the immense scale and friction involved. The two tectonic plates can become locked together for centuries, building up an enormous amount of stress. When this stress is finally released, the plates slip suddenly, causing a massive earthquake. The fault areas in these zones are the largest on the planet, allowing for the biggest ruptures.
6. What happens to a tectonic plate after it subducts into the mantle?
As a tectonic plate sinks into the hot mantle, it heats up and undergoes significant changes. Water trapped in the minerals of the subducting slab is released, which lowers the melting point of the overlying mantle rock, causing it to melt and form magma. This magma is less dense than the surrounding rock and rises to the surface, often resulting in explosive volcanic eruptions.
7. What is the key difference in the landforms created by oceanic-continental and oceanic-oceanic subduction?
The main difference lies in the location and type of volcanic features they create. Oceanic-continental subduction forms a long chain of volcanoes on a continent, known as a volcanic arc (e.g., the Cascade Range in North America). In contrast, oceanic-oceanic subduction forms a curved line of volcanic islands out in the ocean, called an island arc (e.g., the Philippines).
