Continental margins refer to the an ar of shift from the land come the deep seafloor, i.e. In between continental and also oceanic crust. In an active continental margin, the boundary between the continent and also the ocean is also a tectonic key boundary, so over there is a lot of geological activity around the margin. The west coast of the United claims is an example of an active margin, wherein the shore corresponds with the boundary in between the Pacific and North America Plates. A passive continental margin occurs whereby the shift from land come sea is not linked with a key boundary. The east coast of the United claims is a good example; the plate boundary is situated along the mid Atlantic ridge, far from the coast. Passive margins are less geologically active. Figure 1.2.1 shows an idealized passive margin. When examining this figure, and also others like it, keep in mind that there is far-reaching vertical exaggeration; the depth range covers about 5000 m, if the horizontal scale extends roughly 300 km. This provides the functions look lot steeper 보다 they in reality are. The bar in ~ the bottom of number 1.2.1 reflects what a passive margin would certainly look choose without this exaggeration; over there is a much much more gradual transition to depth.
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The continental shelf is the shallow, submarine edge of the continent. Geologically the shelf is still part of the continental crust, however it is often overlaid with naval sediments. Top top average, the shelf extends about 80 km from the coast; some margins have very little shelf, when the Siberian Shelf in the Arctic extends roughly 1500 km. The depth that the shelf usually remains below around 150 m, and also the floor of the shelf is fairly flat. The level topography is the an outcome of alters in sea level; throughout history the shelves have actually been both submerged and also exposed, and as sea level rose and fell, tide action, ice sheets, and other erosional procedures smoothed the end the shelf surface. Wave activity and the motion of sediments over the shelf have continued this smoothing process. Continental shelves just make up about 6% the the ocean’s surface ar area, however they space biologically one of the richest parts of the ocean; their shallow depth avoids nutrients native sinking out, and their proximity to the coastline provides far-reaching nutrient input. The continental shelf ends at the shelf break, i beg your pardon is the allude where the angle of the seafloor begins to obtain steeper. The shelf break averages around 135 m deep.
After the shelf break, the seafloor takes on a steeper edge (about 4o) together it descends come the deep ocean. This steeper portion of the margin is the continental slope, and it extends from the shelf malfunction to 3000-5000m. In some components of the ocean, huge submarine canyons have been sculpted into the continental slope; for example, Monterey Canyon in Monterey Bay, California, is a submarine canyon similar in size to the grand Canyon! these canyons might be sculpted out by turbidity currents, i beg your pardon are basically landslides that sediment, rocks, and also other debris under the challenge of the slope.
At the bottom that the steep is the continental rise. This area represents whereby the continent crust meets the oceanic crust, as the slope begins to level turn off to come to be the deep s floor. The rise consists of a special layer of built up sediment coming from the continent, so it is complicated to tell whereby the steep ends and the rise begins.
After the climb comes the abyssal plain, or the deep ocean floor, lying in between 4500 – 6000 m. The abyssal plain consists of most that the s floor, and is the flattest an ar on Earth. That is flat as result of millions of years of sediment buildup on the bottom, i beg your pardon buries numerous bottom features (Figure 1.2.2).
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Passive margins, as described above, have broad shelves, gentle slopes, and a well-developed rise. Due to the fact that passive margins are not bowl boundaries, castle experience lengthy periods of loved one stability which deserve to lead come the development of this features. Energetic margins have similar features come passive margins, but the plate border affects the properties of the features. Energetic margins, like the Pacific coastline of phibìc America, have actually narrower shelves, steeper slopes, and little to no rise, an especially in convergent boundaries. Trenches associated with subduction area act as sediment traps, avoiding the build-up of a continental rise, and keeping sediments turn off of the abyssal plains.
* “Physical Geology” by Steven Earle supplied under a CC-BY 4.0 global license. Download this book for complimentary at http://open.bccampus.ca