Continental margins describe the an ar of shift from the land come the deep seafloor, i.e. Between continental and also oceanic crust. In one active continental margin, the boundary between the continent and also the s is also a tectonic key boundary, so there is a the majority of geological task around the margin. The west shore of the United says is an example of an active margin, wherein the coastline corresponds with the boundary between the Pacific and also North America Plates. A passive continent margin occurs wherein the change from land come sea is not linked with a key boundary. The east coast of the United claims is a good example; the plate border is located along the mid Atlantic ridge, much from the coast. Passive spare are less geologically active. Figure 1.2.1 shows an idealized passive margin. When assessing this figure, and also others like it, note that over there is significant vertical exaggeration; the depth range covers around 5000 m, if the horizontal scale extends roughly 300 km. This provides the functions look much steeper than they actually are. The bar in ~ the bottom of number 1.2.1 mirrors what a passive margin would certainly look favor without this exaggeration; there is a much much more gradual change to depth.
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The continental shelf is the shallow, flooded edge the the continent. Geologically the shelf is still component of the continent crust, yet it is frequently overlaid with maritime sediments. Top top average, the shelf extends around 80 km from the coast; some margins have very little shelf, if the Siberian Shelf in the Arctic extends approximately 1500 km. The depth of the shelf normally remains below about 150 m, and also the floor that the shelf is reasonably flat. The flat topography is the an outcome of transforms in sea level; throughout history the shelves have been both submerged and also exposed, and as sea level rose and fell, wave action, ice cream sheets, and other erosional processes smoothed out the shelf surface. Wave action and the movement of sediments over the shelf have continued this smoothing process. Continent shelves only make up about 6% the the ocean’s surface ar area, but they are biologically among the richest parts of the ocean; their shallow depth avoids nutrients from sinking out, and also their proximity come the coast provides far-reaching nutrient input. The continent shelf end at the shelf break, i beg your pardon is the point where the edge of the seafloor starts to get steeper. The shelf break averages around 135 m deep.
After the shelf break, the seafloor takes on a steeper angle (about 4o) as it descends to the deep ocean. This steeper section of the margin is the continental slope, and it extends native the shelf breakdown to 3000-5000m. In some parts of the ocean, big submarine canyons have actually been carved into the continental slope; because that 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 m sorry are basically landslides of sediment, rocks, and also other debris under the face of the slope.
At the bottom of the steep is the continental rise. This area represents wherein the continental crust meets the oceanic crust, as the slope begins to level off to come to be the deep s floor. The rise is composed of a thick layer of gathered sediment comes from the continent, so that is daunting to tell where the slope ends and also the climb begins.
After the increase comes the abyssal plain, or the deep ocean floor, lying between 4500 – 6000 m. The abyssal plain includes most of the s floor, and also is the flattest an ar on Earth. It is flat because of millions of year of sediment build-up on the bottom, i beg your pardon buries countless bottom features (Figure 1.2.2).
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Passive margins, as defined above, have vast shelves, gentle slopes, and a well-developed rise. Due to the fact that passive margins space not plate boundaries, they experience long periods of loved one stability which have the right to lead to the advance of this features. Active margins have similar features come passive margins, but the plate boundary affects the nature of the features. Active margins, favor the Pacific coastline of phibìc America, have actually narrower shelves, steeper slopes, and tiny to no rise, specifically in convergent boundaries. Trenches associated with subduction zones act as sediment traps, staying clear of the accumulation of a continent rise, and keeping sediments turn off of the abyssal plains.
* “Physical Geology” through Steven Earle used under a CC-BY 4.0 worldwide license. Download this book for totally free at http://open.bccampus.ca