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ThatDamnedPanda -> RE: Giant Crack in Africa Will Create a New Ocean (11/4/2009 9:31:35 PM)
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quote:
ORIGINAL: Louve00
quote:
ORIGINAL: Sanity
Slabs like this that sink oceanic crust are called subduction zones, and those adjacent to Japan produce intense and damaging seismic activity. "We have discovered an analogous subduction zone, deep inside the Earth below the central Mississippi River Valley," Forte said.
Full article here:
http://www.livescience.com/environment/070502_newmadrid_quake.html
Yes, I saw that about subduction zones. From the way I understood it, its tactonic plates that aren't level and are askew to each other. Their shift causes a sinking in one area and a build up (sort of land crumbling up into a pile), in the area next to the sinking. There's one of the biggest, if not the biggest that is supposedly in the pacific ocean (somewhere in the zone between Japan, Hawaii, and Alaska, I think). That's supposed to be something thats going to shift again in the future and will cause big tsunami's along the pacific coast.
The Ring of Fire - essentially the entire rim of the Pacific Ocean, from the tip of South America all the way to Alaska, then around Kamchtaka and down the eastern edge of Asia to around Indonesia, then sharply eastward past the northeastern edge of Australia, then doglegging sharply south through the Tonga Trench. It's by far the most geologically active area of the Earth, accounting for 90% of the planet's earthquakes and 75% of the volcanoes.
The way subduction works is relatively simple, on the face of it (although the exact mechanics are poorly understood). Oceanic plates are both thinner and denser than continental plates, so when the two types of plates collide, the oceanic plate slides down underneath the thicker, but lighter, continental plate. Thus the oceanic plate "subducts", and the area where the plates meet is a "subduction zone." As the lighter continental plate is forced up over the oceanic plate, friction between the two masses causes the plates to lock together for long periods of time until the momentum behind the moving plates becomes so great that it breaks free and lurches several inches, or even several meters, instantaneously. Smaller movements produce smaller earthquakes, but in places where the stress has not been relieved for long periods of time, the movement can be as much as 7 to 10 meters - or more. When this much mass moves that far and that suddenly, it's a major quake, and since the subduction zones are underwater, the sudden displacement of huge volumes of water can often cause a devastating tsunami.
quote:
ORIGINAL: Louve00
I can only imagine (well, really I can't imagine it lol), what would happen if something like that started happening in the heartland region of the US. I'm no scientist by any means, but it makes me wonder if something like that (aside from earthquakes) could form a crack like in Africa, that could also lead to another ocean? But maybe not. According to your link, the ground is ripping apart underneath (in Africa). Subduction zones are an uneven collision, not a seperation.
Just as subduction zones occur on the front edges of moving tectonic plates, rift zones form at the back edges. The mid-Atlantic Ridge, for example, is a rift zone on the back edge of the North American Plate, the same plate whose front edge is riding up over the top of the Pacific Plate in the Ring of Fire. What is happening in Africa is an area of separation called the East African Rift Zone, a portion of the Aftican Plate that is pulling apart. The thing is, though, that nobody really knows for certain why. There are various theories - the crust in that portion of the plate just happens to be weaker, or there is a hot plume from the mantle rising just beneath the rift, or a combination of the two factors, or something else entirely - but nobody really knows for sure. So nobody can really say where other rift zones may form.
Can it happen in North America? It already did. About 1.1 billion years ago, a rift (the Midcontinent Rift System) began to tear the North American Plate in half, right down the middle - from what is now southern Canada all the way to Kansas. Lake Superior is the northern end of it, part of the Saint Croix River just 10 miles east of my house follows the path of it, and the entire North Shore of Lake Superior is lined with extinct volcanoes from the intense, almost constant volcanic eruptions that blanketed tens of thousands of square miles of North America with basaltic lava flows for tens of millions of years. For about 20 to 25 million years, the continent slowly pulled itself apart, and then... it just stopped.
Geologists don't know what stopped it, but they are fairly certain that it stopped just on the very brink of becoming an ocean. The Midcontinent Rift System is the largest "healed" rift on Earth; every other rift that is larger than this one did, in fact, become an ocean. Why did this one stop tearing the continent in half? Nobody knows. And nobody knows why it started, either - so nobody really knows for sure that it won't happen again, either there or someplace else. It's not likely, but... it is possible. Nothing we can do except get up and check the basement floor ver-r-r-ry carefully for fresh cracks every morning.
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