Now that we know the terminology, we can look at the Mid-Atlantic Ridge. The German term for a graben is Graben (literally "trench"). The illustration below is from Wikipedia. rift-valley or grabenĪ graben or rift valley is formed where tectonic plates move away from each other and part of the broken crust sinks. The German term for an oceanic trench is Tiefseerinne (literally "deep sea groove"). has also provided an illuminating illustration. So scientists were flummoxed as to how its seafloor was expanding.Let's clear up the terminology first: trenchĪ trench, as has described in their answer, is formed where tectonic plates move towards each other and one of the plates is subducted under the other. The Atlantic Ocean, however, sits atop four major plates with boundaries that don't match continental borders - the boundaries occur in the middle of the ocean. Subduction at these boundaries causes the earthquakes and volcanic eruptions that characterize the region's aptly named "Ring of Fire." That's why the Pacific Ocean expands faster than the Atlantic: Most of the Pacific sits atop one tectonic plate, and its boundaries line up almost perfectly with the continental ones on the east and west sides, the North American and Eurasian plates. They also knew plates move apart most markedly at subduction zones, which typically occur at active continental margins - where the boundary between a continent and the ocean is also a tectonic plate boundary. Researchers knew that oceans expand and contract at different rates. The discovery helps solve a longstanding geological puzzle. One of the remote seismometers deployed by University of Southampton scientists in the Atlantic Ocean. Material from the lower mantle, the part closest to the core, isn't generally found bursting crustward there.īut the new study found that the Mid-Atlantic Ridge is a convection hotspot. Generally, any upward oozing of material under tectonic boundaries like the Mid-Atlantic Ridge usually starts from a part of the mantle very close to the Earth's surface, about 2 miles below the crust. This process, known as convection, typically happens when two plates collide and one subducts, or sinks, under another. These plates surf atop the mantle, moving around as hotter, less dense material from deep within the Earth rises toward to the crust, and colder, denser material sinks towards the core.
The top layer of the truffle - only about 21 miles thick - is the Earth's crust, which is fragmented into tectonic plates that fit together like a puzzle. The center consists of a 1,800-mile-thick, semi-solid mantle that encircles a super-hot core. Imagine the Earth as a chocolate truffle - a viscous center ensconced in a hardened shell.
NASA Earth Observatory maps by Joshua Stevens, using data from Sandwell, D. The mid-Atlantic ridge, seen in deep orange, on a NASA Earth Observatory bathymetry map.
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