A peninsula is a landform that extends from a mainland and is surrounded by water on most sides. Peninsulas exist on each continent. The largest peninsula in the world is the Arabian Peninsula .
75-529: The Samaná Península is a peninsula in Dominican Republic situated in the province of Samaná . The Samaná Peninsula is connected to the rest of the state by the isthmus of Samaná; to its south is Samaná Bay . The peninsula contains many beaches , especially in the city of Santa Bárbara de Samaná . It contains three rivers. The peninsula was originally inhabited by the Ciguayos , which spoke
150-469: A basin . This may create peninsulas, and occurred for example in the Keweenaw Peninsula . In the case of formation from meltwater, melting glaciers deposit sediment and form moraines , which act as dams for the meltwater. This may create bodies of water that surround the land, forming peninsulas. If deposition formed the peninsula, the peninsula was composed of sedimentary rock , which
225-418: A mid-ocean ridge , where the volcanic rock is still relatively young, most parts of the seafloor are covered in sediment . This material comes from several different sources and is highly variable in composition. Seafloor sediment can range in thickness from a few millimetres to several tens of kilometres. Near the surface seafloor sediment remains unconsolidated, but at depths of hundreds to thousands of metres
300-444: A Petri dish. In areas where diatoms are abundant, the underlying sediment is rich in silica diatom tests, and is called diatomaceous earth . Radiolarians are planktonic protozoans (making them part of the zooplankton), that like diatoms, secrete a silica test. The test surrounds the cell and can include an array of small openings through which the radiolarian can extend an amoeba-like "arm" or pseudopod. Radiolarian tests often display
375-421: A change in conditions, such as a change in temperature, pressure, or pH, which reduces the amount of a substance that can remain in a dissolved state. There is not a lot of hydrogenous sediment in the ocean compared to lithogenous or biogenous sediments, but there are some interesting forms. In hydrothermal vents seawater percolates into the seafloor where it becomes superheated by magma before being expelled by
450-449: A few millimetres per million years. For that reason, they only form in areas where there are low rates of lithogenous or biogenous sediment accumulation, because any other sediment deposition would quickly cover the nodules and prevent further nodule growth. Therefore, manganese nodules are usually limited to areas in the central ocean, far from significant lithogenous or biogenous inputs, where they can sometimes accumulate in large numbers on
525-408: A few millimetres to several tens of kilometres. Near the surface, the sea-floor sediments remain unconsolidated, but at depths of hundreds to thousands of metres (depending on the type of sediment and other factors) the sediment becomes lithified . The various sources of seafloor sediment can be summarized as follows: The distributions of some of these materials around the seas are shown in
600-443: A global scale. So cosmogenous and hydrogenous sediments can mostly be ignored in the discussion of global sediment patterns. Coarse lithogenous/terrigenous sediments are dominant near the continental margins as land runoff , river discharge , and other processes deposit vast amounts of these materials on the continental shelf . Much of this sediment remains on or near the shelf, while turbidity currents can transport material down
675-478: A higher proportion of O18 isotope. This means the ratio of O16:O18 in shells is low during periods of colder climate. When climate warms, glacial ice melts releasing O16 from the ice and returning it to the oceans, increasing the O16:O18 ratio in the water. When organisms incorporate oxygen into their shells, the shells will contain a higher O16:O18 ratio. Scientists can therefore examine biogenous sediments, calculate
750-422: A much faster rate, so they accumulate below their point of origin before the currents can disperse them. Most of the tests do not sink as individual particles; about 99% of them are first consumed by some other organism, and are then aggregated and expelled as large fecal pellets , which sink much more quickly and reach the ocean floor in only 10–15 days. This does not give the particles as much time to disperse, and
825-509: A number of interlocking CaCO 3 plates (coccoliths) that form a sphere surrounding the cell. When coccolithophores die the individual plates sink out and form an ooze. Over time, the coccolithophore ooze lithifies to becomes chalk. The White Cliffs of Dover in England are composed of coccolithophore-rich ooze that turned into chalk deposits. Foraminiferans (also referred to as forams ) are protozoans whose tests are often chambered, similar to
SECTION 10
#1732765278161900-476: A number of rays protruding from their shells which aid in buoyancy. Oozes that are dominated by diatom or radiolarian tests are called siliceous oozes . Like the siliceous sediments, the calcium carbonate, or calcareous sediments are also produced from the tests of microscopic algae and protozoans; in this case the coccolithophores and foraminiferans. Coccolithophores are single-celled planktonic algae about 100 times smaller than diatoms. Their tests are composed of
975-456: A rate of about one centimetre per thousand years, while small clay particles are deposited in the deep ocean at around one millimetre per thousand years. Sediments from the land are deposited on the continental margins by surface runoff , river discharge , and other processes. Turbidity currents can transport this sediment down the continental slope to the deep ocean floor. The deep ocean floor undergoes its own process of spreading out from
1050-434: Is a bioessential element and is efficiently recycled in the marine environment through the silica cycle . Distance from land masses, water depth and ocean fertility are all factors that affect the opal silica content in seawater and the presence of siliceous oozes. The term calcareous can be applied to a fossil, sediment, or sedimentary rock which is formed from, or contains a high proportion of, calcium carbonate in
1125-454: Is a common mineral in terrestrial rocks, and it is very hard and resistant to abrasion. Over time, particles made from other materials are worn away, leaving only quartz behind. Beach sand is a very mature sediment; it is composed primarily of quartz, and the particles are rounded and of similar size (well-sorted). Marine sediments can also classified by their source of origin. There are four types: Lithogenous or terrigenous sediment
1200-403: Is a form of calcium carbonate derived from planktonic organisms that accumulates on the sea floor . This can only occur if the ocean is shallower than the carbonate compensation depth . Below this depth, calcium carbonate begins to dissolve in the ocean, and only non-calcareous sediments are stable, such as siliceous ooze or pelagic red clay . Where and how sediments accumulate will depend on
1275-777: Is a type of biogenic pelagic sediment located on the deep ocean floor . Siliceous oozes are the least common of the deep sea sediments, and make up approximately 15% of the ocean floor. Oozes are defined as sediments which contain at least 30% skeletal remains of pelagic microorganisms. Siliceous oozes are largely composed of the silica based skeletons of microscopic marine organisms such as diatoms and radiolarians . Other components of siliceous oozes near continental margins may include terrestrially derived silica particles and sponge spicules. Siliceous oozes are composed of skeletons made from opal silica Si(O 2 ) , as opposed to calcareous oozes , which are made from skeletons of calcium carbonate organisms (i.e. coccolithophores ). Silica (Si)
1350-483: Is another way to categorize sediment texture. Sorting refers to how uniform the particles are in terms of size. If all of the particles are of a similar size, such as in beach sand , the sediment is well-sorted. If the particles are of very different sizes, the sediment is poorly sorted, such as in glacial deposits . A third way to describe marine sediment texture is its maturity, or how long its particles have been transported by water. One way which can indicate maturity
1425-474: Is how round the particles are. The more mature a sediment the rounder the particles will be, as a result of being abraded over time. A high degree of sorting can also indicate maturity, because over time the smaller particles will be washed away, and a given amount of energy will move particles of a similar size over the same distance. Lastly, the older and more mature a sediment the higher the quartz content, at least in sediments derived from rock particles. Quartz
1500-414: Is primarily composed of small fragments of preexisting rocks that have made their way into the ocean. These sediments can contain the entire range of particle sizes, from microscopic clays to large boulders, and they are found almost everywhere on the ocean floor. Lithogenous sediments are created on land through the process of weathering, where rocks and minerals are broken down into smaller particles through
1575-465: Is thought to have come from river discharge, particularly from Asia. Most of this sediment, especially the larger particles, will be deposited and remain fairly close to the coastline, however, smaller clay particles may remain suspended in the water column for long periods of time and may be transported great distances from the source. Wind: Windborne (aeolian) transport can take small particles of sand and dust and move them thousands of kilometres from
SECTION 20
#17327652781611650-429: Is very resistant to abrasion, so it is a dominant component of lithogenous sediments, including sand. Biogenous sediments come from the remains of living organisms that settle out as sediment when the organisms die. It is the "hard parts" of the organisms that contribute to the sediments; things like shells, teeth or skeletal elements, as these parts are usually mineralized and are more resistant to decomposition than
1725-859: The Ciguayo language at the time of Spanish intervention. The main roads are the DR-5 and the Samaná Highway, which leads from the peninsula to Santo Domingo . The peninsula also contains the Samaná El Catey International Airport . The peninsula also hosts agriculture and tourism. This Dominican Republic location article is a stub . You can help Misplaced Pages by expanding it . Peninsula The word peninsula derives from Latin paeninsula , from paene 'almost' and insula 'island'. The word entered English in
1800-423: The continental margins where they can be over 10 km thick. This is because the crust near passive continental margins is often very old, allowing for a long period of accumulation, and because there is a large amount of terrigenous sediment input coming from the continents. Near mid-ocean ridge systems where new oceanic crust is being formed, sediments are thinner, as they have had less time to accumulate on
1875-421: The diatoms (algae) and the radiolarians ( protozoans ). Diatoms are particularly important members of the phytoplankton, functioning as small, drifting algal photosynthesizers. A diatom consists of a single algal cell surrounded by an elaborate silica shell that it secretes for itself. Diatoms come in a range of shapes, from elongated, pennate forms, to round, or centric shapes that often have two halves, like
1950-418: The seafloor . These particles either have their origins in soil and rocks and have been transported from the land to the sea, mainly by rivers but also by dust carried by wind and by the flow of glaciers into the sea, or they are biogenic deposits from marine organisms or from chemical precipitation in seawater, as well as from underwater volcanoes and meteorite debris. Except within a few kilometres of
2025-435: The start of this article ↑ shows the distribution of the major types of sediment on the ocean floor. Cosmogenous sediments could potentially end up in any part of the ocean, but they accumulate in such small abundances that they are overwhelmed by other sediment types and thus are not dominant in any location. Similarly, hydrogenous sediments can have high concentrations in specific locations, but these regions are very small on
2100-572: The 16th century. A peninsula is generally defined as a piece of land surrounded on most sides by water. A peninsula may be bordered by more than one body of water, and the body of water does not have to be an ocean or a sea. A piece of land on a very tight river bend or one between two rivers is sometimes said to form a peninsula, for example in the New Barbadoes Neck in New Jersey , United States. A peninsula may be connected to
2175-470: The Bahamas. Methane hydrates are another type of hydrogenous deposit with a potential industrial application. All terrestrial erosion products include a small proportion of organic matter derived mostly from terrestrial plants. Tiny fragments of this material plus other organic matter from marine plants and animals accumulate in terrigenous sediments, especially within a few hundred kilometres of shore. As
2250-668: The Mediterranean Sea. Beginning around 6 million years ago, tectonic processes closed off the Mediterranean Sea from the Atlantic, and the warm climate evaporated so much water that the Mediterranean was almost completely dried out, leaving large deposits of salt in its place (an event known as the Messinian Salinity Crisis ). Eventually the Mediterranean re-flooded about 5.3 million years ago, and
2325-550: The O16:O18 ratios for samples of known ages, and from those ratios, infer the climate conditions under which those shells were formed. The same types of measurements can also be taken from ice cores; a decrease of 1 ppm O18 between ice samples represents a decrease in temperature of 1.5°C. The primary sources of microscopic biogenous sediments are unicellular algaes and protozoans (single-celled amoeba-like creatures) that secrete tests of either calcium carbonate (CaCO 3 ) or silica (SiO 2 ). Silica tests come from two main groups,
Samaná Peninsula - Misplaced Pages Continue
2400-405: The action of wind, rain, water flow, temperature- or ice-induced cracking, and other erosive processes. These small eroded particles are then transported to the oceans through a variety of mechanisms: Streams and rivers: Various forms of runoff deposit large amounts of sediment into the oceans, mostly in the form of finer-grained particles. About 90% of the lithogenous sediment in the oceans
2475-448: The amount of material coming from a source, the distance from the source, the amount of time that sediment has had to accumulate, how well the sediments are preserved, and the amounts of other types of sediments that are also being added to the system. Rates of sediment accumulation are relatively slow throughout most of the ocean, in many cases taking thousands of years for any significant deposits to form. Lithogenous sediment accumulates
2550-403: The atmosphere that eventually settle back down to Earth and contribute to the sediments. Like spherules, meteor debris is mostly silica or iron and nickel. One form of debris from these collisions are tektites , which are small droplets of glass. They are likely composed of terrestrial silica that was ejected and melted during a meteorite impact, which then solidified as it cooled upon returning to
2625-400: The bottom! Given that slow descent, a current of only 1 cm/sec could carry the test as much as 15,000 km away from its point of origin before it reaches the bottom. Despite this, the sediments in a particular location are well-matched to the types of organisms and degree of productivity that occurs in the water overhead. This means the sediment particles must be sinking to the bottom at
2700-420: The bottom. While calcite is insoluble in surface water, its solubility increases with depth (and pressure) and at around 4,000 m, the carbonate fragments dissolve. This depth, which varies with latitude and water temperature, is known as the carbonate compensation depth . As a result, carbonate oozes are absent from the deepest parts of the ocean (deeper than 4,000 m), but they are common in shallower areas such as
2775-499: The case of Florida , continental drift, marine sediment, and marine transgressions were all contributing factors to its shape. In the case of formation from glaciers (e.g., the Antarctic Peninsula or Cape Cod ), peninsulas can be created due to glacial erosion , meltwater or deposition . If erosion formed the peninsula, softer and harder rocks were present, and since the glacier only erodes softer rock, it formed
2850-492: The climate-change implications of its extraction and use can see that this would be folly. Cosmogenous sediment is derived from extraterrestrial sources, and comes in two primary forms; microscopic spherules and larger meteor debris. Spherules are composed mostly of silica or iron and nickel, and are thought to be ejected as meteors burn up after entering the atmosphere. Meteor debris comes from collisions of meteorites with Earth. These high impact collisions eject particles into
2925-409: The coccolithophores that also produced calcium carbonate tests. Discoaster tests were star-shaped, and reached sizes of 5-40 μm across. Discoasters went extinct approximately 2 million years ago, but their tests remain in deep, tropical sediments that predate their extinction. Because of their small size, these tests sink very slowly; a single microscopic test may take about 10–50 years to sink to
3000-453: The continental shelf and reach the deep ocean floor. Lithogenous sediments usually reflect the composition of whatever materials they were derived from, so they are dominated by the major minerals that make up most terrestrial rock. This includes quartz, feldspar, clay minerals, iron oxides, and terrestrial organic matter. Quartz (silicon dioxide, the main component of glass) is one of the most common minerals found in nearly all rocks, and it
3075-603: The deepest parts of the ocean, and most of this clay is terrestrial in origin. Siliceous oozes (derived from radiolaria and diatoms) are common in the south polar region, along the equator in the Pacific, south of the Aleutian Islands, and within large parts of the Indian Ocean. Carbonate oozes are widely distributed in all of the oceans within equatorial and mid-latitude regions. In fact, clay settles everywhere in
Samaná Peninsula - Misplaced Pages Continue
3150-440: The diagram at the start of this article ↑ . Terrigenous sediments predominate near the continents and within inland seas and large lakes. These sediments tend to be relatively coarse, typically containing sand and silt, but in some cases even pebbles and cobbles. Clay settles slowly in nearshore environments, but much of the clay is dispersed far from its source areas by ocean currents. Clay minerals are predominant over wide areas in
3225-425: The extraction of these non-renewable resources. Evaporites are hydrogenous sediments that form when seawater evaporates, leaving the dissolved materials to precipitate into solids, particularly halite (salt, NaCl). In fact, the evaporation of seawater is the oldest form of salt production for human use, and is still carried out today. Large deposits of halite evaporites exist in a number of places, including under
3300-557: The fastest, on the order of one metre or more per thousand years for coarser particles. However, sedimentation rates near the mouths of large rivers with high discharge can be orders of magnitude higher. Biogenous oozes accumulate at a rate of about 1 cm per thousand years, while small clay particles are deposited in the deep ocean at around one millimetre per thousand years. As described above, manganese nodules have an incredibly slow rate of accumulation, gaining 0.001 millimetres per thousand years. Marine sediments are thickest near
3375-464: The fleshy "soft parts" that rapidly deteriorate after death. Macroscopic sediments contain large remains, such as skeletons, teeth, or shells of larger organisms. This type of sediment is fairly rare over most of the ocean, as large organisms do not die in enough of a concentrated abundance to allow these remains to accumulate. One exception is around coral reefs ; here there is a great abundance of organisms that leave behind their remains, in particular
3450-415: The form of calcite or aragonite . Calcareous sediments ( limestone ) are usually deposited in shallow water near land, since the carbonate is precipitated by marine organisms that need land-derived nutrients. Generally speaking, the farther from land sediments fall, the less calcareous they are. Some areas can have interbedded calcareous sediments due to storms, or changes in ocean currents. Calcareous ooze
3525-562: The fragments of the stony skeletons of corals that make up a large percentage of tropical sand. Microscopic sediment consists of the hard parts of microscopic organisms, particularly their shells, or tests . Although very small, these organisms are highly abundant and as they die by the billions every day their tests sink to the bottom to create biogenous sediments. Sediments composed of microscopic tests are far more abundant than sediments from macroscopic particles, and because of their small size they create fine-grained, mushy sediment layers. If
3600-419: The halite deposits were covered by other sediments, but they still remain beneath the seafloor. Oolites are small, rounded grains formed from concentric layers of precipitation of material around a suspended particle. They are usually composed of calcium carbonate, but they may also from phosphates and other materials. Accumulation of oolites results in oolitic sand, which is found in its greatest abundance in
3675-513: The isotopes). O16 is the most common form, followed by O18 (O17 is rare). O16 is lighter than O18, so it evaporates more easily, leading to water vapor that has a higher proportion of O16. During periods of cooler climate, water vapor condenses into rain and snow, which forms glacial ice that has a high proportion of O16. The remaining seawater therefore has a relatively higher proportion of O18. Marine organisms which incorporate dissolved oxygen into their shells as calcium carbonate will have shells with
3750-426: The largest with grain diameters of 256 mm or larger. Among other things, grain size represents the conditions under which the sediment was deposited. High energy conditions, such as strong currents or waves, usually results in the deposition of only the larger particles as the finer ones will be carried away. Lower energy conditions will allow the smaller particles to settle out and form finer sediments. Sorting
3825-622: The low temperatures typical of the seafloor (close to 4 °C), water and methane combine to create a substance known as methane hydrate. Within a few metres to hundreds of metres of the seafloor, the temperature is low enough for methane hydrate to be stable and hydrates accumulate within the sediment. Methane hydrate is flammable because when it is heated, the methane is released as a gas. The methane within seafloor sediments represents an enormous reservoir of fossil fuel energy. Although energy corporations and governments are anxious to develop ways to produce and sell this methane, anyone that understands
SECTION 50
#17327652781613900-531: The mainland via an isthmus , for example, in the Isthmus of Corinth which connects to the Peloponnese peninsula. Peninsulas can be formed from continental drift , glacial erosion , glacial meltwater , glacial deposition , marine sediment , marine transgressions , volcanoes, divergent boundaries or river sedimentation. More than one factor may play into the formation of a peninsula. For example, in
3975-660: The mid-Atlantic ridge, the East Pacific Rise (west of South America), along the trend of the Hawaiian/Emperor Seamounts (in the northern Pacific), and on the tops of many isolated seamounts. Sediment texture can be examined in several ways. The first way is grain size . Sediments can be classified by particle size according to the Wentworth scale . Clay sediments are the finest with a grain diameter of less than .004 mm and boulders are
4050-555: The mid-ocean ridge, and then slowly subducts accumulated sediment on the deep floor into the molten interior of the earth. In turn, molten material from the interior returns to the surface of the earth in the form of lava flows and emissions from deep sea hydrothermal vents , ensuring the process continues indefinitely. The sediments provide habitat for a multitude of marine life , particularly of marine microorganisms . Their fossilized remains contain information about past climates , plate tectonics , ocean circulation patterns, and
4125-411: The nodule to grow over time. The composition of the nodules can vary somewhat depending on their location and the conditions of their formation, but they are usually dominated by manganese- and iron oxides. They may also contain smaller amounts of other metals such as copper, nickel and cobalt. The precipitation of manganese nodules is one of the slowest geological processes known; they grow on the order of
4200-443: The ocean and begins to break apart or melt, these particles get deposited. Most of the deposition will happen close to where the glacier meets the water, but a small amount of material is also transported longer distances by rafting, where larger pieces of ice drift far from the glacier before releasing their sediment. Gravity: Landslides, mudslides, avalanches, and other gravity-driven events can deposit large amounts of material into
4275-489: The ocean are gastroliths. Gastrolith means "stomach stone". Many animals, including seabirds, pinnipeds, and some crocodiles deliberately swallow stones and regurgitate them latter. Stones swallowed on land can be regurgitated at sea. The stones can help grind food in the stomach or act as ballast regulating buoyancy. Mostly these processes deposit lithogenous sediment close to shore. Sediment particles can then be transported farther by waves and currents, and may eventually escape
4350-444: The ocean when they happen close to shore. Waves: Wave action along a coastline will erode rocks and will pull loose particles from beaches and shorelines into the water. Volcanoes: Volcanic eruptions emit vast amounts of ash and other debris into the atmosphere, where it can then be transported by wind to eventually get deposited in the oceans. Gastroliths : Another, relatively minor, means of transporting lithogenous sediment to
4425-452: The oceans, but in areas where silica- and carbonate-producing organisms are prolific, they produce enough silica or carbonate sediment to dominate over clay. Carbonate sediments are derived from a wide range of near-surface pelagic organisms that make their shells out of carbonate. These tiny shells, and the even tinier fragments that form when they break into pieces, settle slowly through the water column, but they don't necessarily make it to
4500-476: The seafloor (Figure 12.4.2 right). Because the nodules contain a number of commercially valuable metals, there has been significant interest in mining the nodules over the last several decades, although most of the efforts have thus far remained at the exploratory stage. A number of factors have prevented large-scale extraction of nodules, including the high costs of deep sea mining operations, political issues over mining rights, and environmental concerns surrounding
4575-435: The seafloor and the other half suspected from water column indicators and/or seafloor deposits. Manganese nodules are rounded lumps of manganese and other metals that form on the seafloor, generally ranging between 3–10 cm in diameter, although they may sometimes reach up to 30 cm. The nodules form in a manner similar to pearls; there is a central object around which concentric layers are slowly deposited, causing
SECTION 60
#17327652781614650-497: The sediment becomes lithified (turned to rock). Rates of sediment accumulation are relatively slow throughout most of the ocean, in many cases taking thousands of years for any significant deposits to form. Sediment transported from the land accumulates the fastest, on the order of one metre or more per thousand years for coarser particles. However, sedimentation rates near the mouths of large rivers with high discharge can be orders of magnitude higher. Biogenous oozes accumulate at
4725-415: The sediment below will reflect the production occurring near the surface. The increased rate of sinking through this mechanism has been called the "fecal express". Seawater contains many different dissolved substances. Occasionally chemical reactions occur that cause these substances to precipitate out as solid particles, which then accumulate as hydrogenous sediment. These reactions are usually triggered by
4800-468: The sediment is deposited, forming a delta peninsula. Marine transgressions (changes in sea level) may form peninsulas, but also may affect existing peninsulas. For example, the water level may change, which causes a peninsula to become an island during high water levels. Similarly, wet weather causing higher water levels make peninsulas appear smaller, while dry weather make them appear larger. Sea level rise from global warming will permanently reduce
4875-403: The sediment layer consists of at least 30% microscopic biogenous material, it is classified as a biogenous ooze. The remainder of the sediment is often made up of clay. Biogenous sediments can allow the reconstruction of past climate history from oxygen isotope ratios. Oxygen atoms exist in three forms, or isotopes, in ocean water: O16 , O17 and O18 (the number refers to the atomic masses of
4950-436: The sediments pile up, the deeper parts start to warm up (from geothermal heat), and bacteria get to work breaking down the contained organic matter. Because this is happening in the absence of oxygen (a.k.a. anaerobic conditions), the by-product of this metabolism is the gas methane (CH 4 ). Methane released by the bacteria slowly bubbles upward through the sediment toward the seafloor. At water depths of 500 m to 1,000 m, and at
5025-444: The shells of snails. As the organism grows, is secretes new, larger chambers in which to reside. Most foraminiferans are benthic, living on or in the sediment, but there are some planktonic species living higher in the water column. When coccolithophores and foraminiferans die, they form calcareous oozes . Older calcareous sediment layers contain the remains of another type of organism, the discoasters ; single-celled algae related to
5100-420: The size of some peninsulas over time. Peninsulas are noted for their use as shelter for humans and Neanderthals . The landform is advantageous because it gives hunting access to both land and sea animals. They can also serve as markers of a nation's borders. Marine sediment Marine sediment , or ocean sediment , or seafloor sediment , are deposits of insoluble particles that have accumulated on
5175-416: The source. These small particles can fall into the ocean when the wind dies down, or can serve as the nuclei around which raindrops or snowflakes form. Aeolian transport is particularly important near desert areas. Glaciers and ice rafting : As glaciers grind their way over land, they pick up lots of soil and rock particles, including very large boulders, that get carried by the ice. When the glacier meets
5250-462: The surface. Cosmogenous sediment is fairly rare in the ocean and it does not usually accumulate in large deposits. However, it is constantly being added to through space dust that continuously rains down on Earth. About 90% of incoming cosmogenous debris is vaporized as it enters the atmosphere, but it is estimated that 5 to 300 tons of space dust land on the Earth's surface each day. Siliceous ooze
5325-463: The timing of major extinctions . Except within a few kilometres of a mid-ocean ridge , where the volcanic rock is still relatively young, most parts of the seafloor are covered in sediments. This material comes from several different sources and is highly variable in composition, depending on proximity to a continent, water depth, ocean currents, biological activity, and climate. Seafloor sediments (and sedimentary rocks ) can range in thickness from
5400-585: The vent. This superheated water contains many dissolved substances, and when it encounters the cold seawater after leaving the vent, these particles precipitate out, mostly as metal sulfides. These particles make up the "smoke" that flows from a vent, and may eventually settle on the bottom as hydrogenous sediment. Hydrothermal vents are distributed along the Earth's plate boundaries, although they may also be found at intra-plate locations such as hotspot volcanoes. Currently there are about 500 known active submarine hydrothermal vent fields, about half visually observed at
5475-564: The volcano erupts near shallow water. Marine sediment may form peninsulas by the creation of limestone . A rift peninsula may form as a result of a divergent boundary in plate tectonics (e.g. the Arabian Peninsula ), while a convergent boundary may also form peninsulas (e.g. Gibraltar or the Indian subcontinent ). Peninsulas can also form due to sedimentation in rivers. When a river carrying sediment flows into an ocean,
5550-403: The younger crust. As distance increases from a ridge spreading center the sediments get progressively thicker, increasing by approximately 100–200 m of sediment for every 1000 km distance from the ridge axis. With a seafloor spreading rate of about 20–40 km/million years, this represents a sediment accumulation rate of approximately 100–200 m every 25–50 million years. The diagram at
5625-504: Was created from a large deposit of glacial drift . The hill of drift becomes a peninsula if the hill formed near water but was still connected to the mainland, for example during the formation of Cape Cod about 23,000 years ago. In the case of formation from volcanoes, when a volcano erupts magma near water, it may form a peninsula (e.g., the Alaskan Peninsula ). Peninsulas formed from volcanoes are especially common when
#160839