Submarine landslides are marine landslides that transport sediment across the continental shelf and into the deep ocean. A submarine landslide is initiated when the downwards driving stress (gravity and other factors) exceeds the resisting stress of the seafloor slope material causing movements along one or more concave to planar rupture surfaces. Submarine landslides take place in a variety of different settings including planes as low as 1° and can cause significant damage to both life and property. Recent advances have been made in understanding the nature and processes of submarine landslides through the use of sidescan sonar and other seafloor mapping technology.
Submarine Landslides have different causes which relate to both the geological attributes of the landslide material and transient environmental factors affecting the submarine environment. Common causes of landslides include: i) presence of weak geological layers, ii) overpressure due to rapid accumulation of sedimentary deposits, iii) earthquakes, iv) storm wave loading and hurricanes, v) gas hydrate dissociation, vi) groundwater seepage and high pore water pressure, vii) glacial loading, viii) volcanic island growth, and ix) oversteepening.
The presence of weak geological layers is a factor which contributes to submarine landslides at all scales. This has been confirmed by seafloor imaging such as swath bathymetric mapping and 3D seismic reflection data. Despite their ubiquity, very little is known about the nature and characteristics of the weak geological layers, as they have rarely been sampled and very little geotechnical work has been conducted on them. An example of a slide which was caused by weak geological layers is the Storegga slide, near Norway which had a total volume of 3,300 km³.
Overpressure due to rapid deposition of sediment is closely related to weak geological layers. An example of landslides caused by overpressure due to rapid deposition occurred in 1969 on the Mississippi delta after Hurricane Camile struck the region.
Earthquakes are a key factor which trigger most major submarine landslides. Earthquakes provide significant environmental stresses and can promote elevated pore water pressure which leads to failure. Earthquakes triggered the Grand Banks landslide of 1929, where a 20 km3 submarine landslide was initiated after an earthquake.
Stormwave loading and hurricanes can lead to submarine landslides in shallow regions and were recognised as one of the factors which contributed to the slides which occurred on the Mississippi delta in 1969 following Hurricane Camille.
A number of studies have indicated that gas hydrates lie beneath many submarine slopes and can contribute to the triggering of a landslide. Gas hydrates are ice-like substances consisting of water and natural gas, which are stable at the temperature and pressure conditions normally found on the seabed. When the temperature rises or the pressure drops the gas hydrate becomes unstable allowing some of the hydrate to dissociate and discharge bubble phase natural gas. If pore water flow is impeded then this gas charging leads to excess pore water pressure and decreased slope stability. Gas hydrate dissociation is thought to have contributed to slides at water depths of 1000 to 1300 m off the east coast of the United States and the Storegga slide off the east coast of Norway.
Groundwater seepage and elevated pore water pressure can cause submarine landslides. Elevated pore water pressure causes reduced frictional resistance to sliding and can result from normal depositional processes, or can be coupled with other causes such as earthquakes, gas hydrate dissociation and glacial loading.
Sediment failure on glacial margins as a result of glacial loading is common and operates on a wide spectrum of dimensions, ranging from relatively small scale mass wasting processes in fjords to large scale slides covering several thousand square kilometres. Factors which are significant in glacial loading induced landslides are the flexing of crust due to the loading and unloading of a fluctuating ice front, variation in drainage and groundwater seepage, quick deposition of low plasticity silts, rapid formation of moraines and till above hemipelagic interstaidal sediments. An example where glacial loading leads to submarine landsliding is the Nyk slide of northern Norway.
Slope failures due to volcanic island growth are among the largest on earth, involving volumes of several cubic kilometres. The failure occurs as large bodies of lava form above weak marine sediments which are prone to failure. Failure is particularly common on edifices which are over 2500 m but rare on edifices which are less than 2500 m. Variation in the behaviour of the slides is significant, with some slides barely keeping up with the growth on the upper part of the volcano while others may surge forward great distances, attaining landslide lengths greater than 200 km. Volcanic island submarine landslides occur in places such as the Hawaiian Islands and the Cape Verde Islands.
In some cases the relationship between the cause and the resulting landslide can be quite clear (e.g. the failure of an oversteepened slope) while in other cases the relationships may not be so obvious. In most cases more than one factor may contribute towards the initiation of a landslide event. This is clearly seen on the Norwegian continental slope where the location of landslides such as Storegga and Traenadjupet is related to weak geological layers. However the position of these weak layers is determined by regional variation in sedimentation style, which itself is controlled by large scale environmental factors such as climate change between glacial and interglacial conditions. Even when considering all the above listed factors, in the end it was calculated that the landslide needed an earthquake for it to ultimately be initiated.
The environments in which submarine landslides are commonly found in are fjords, active river deltas on the continental margin, submarine canyon fan systems, open continental slopes, and oceanic volcanic islands and ridges.
There are a variety of different types of submarine mass movements. All of the movements are mutually exclusive, for example a slide cannot be a fall. Some types of mass movements, such as slides, can be distinguished by the disrupted step like morphology which shows that there was only minor movement of the failed mass. The displaced material on a slide moves on a thin region of high strain. In flows the slide zone will be left bare and the displaced mass may be deposited hundreds of kilometres away from the origin of the slide. The displaced sediment of fall will predominantly travel through the water, falling, bouncing and rolling. Despite the variety of different landslides present in submarine environment, only slides, debris flow and turbidity currents provide a substantial contribution to gravity driven sediment transport.
Recent advances in 3-D seismic mapping have revealed spectacular images of submarine landslides off Angola and Brunei, showing in detail the size of blocks transported and how they moved along the sea floor.
It was initially thought that submarine landslides in cohesive sediments systematically and sequentially developed downslope from slide to debris flow to turbidity current through slowly increasing disintegration and entrainment of water. However it is now thought that this model is likely to be an oversimplification, as some landslides travel many hundreds of kilometres without any noticeable change into turbidity currents, as shown in figure 3 while others completely change into turbidity currents near to the source. This variation in the development of different submarine landslides is associated with the development of velocity vectors in the displaced mass. The in-place stress, sediment properties (particularly density), and morphology of the failed mass will determine whether the slide stops a short distance along the rupture surface or will transform into a flow which travels great distances.
The initial density of the sediment plays a key role in the mobilization into flows and the distances that the slide will travel. If the sediment is a soft, fluid material then the slide is likely to travel great distances and a flow is more likely to occur. However, if the sediment is stiffer then the slide will only travel a short distance and a flow is less likely to occur. Furthermore, the ability to flow may also be dependent upon the amount of energy transferred to the falling sediment throughout the failure event. Often large landslides on the continental margin are complicated and components of slide, debris flow and turbidity current may all be apparent when examining the remains of a submarine landslide.
The primary hazards associated with submarine landslides are the direct destruction of infrastructure and tsunami.
Landslides can have significant economic impacts on infrastructure such as the rupture of fibre optic submarine communications cables and pipelines and damage to offshore drilling platforms and can continue onwards on slope angles as low as 1°. An example of submarine cable damage was discovered in the Grand Banks slide of 1929 where the landslide and resulting turbidity current broke a series of submarine cables up to nearly 600 km away from the beginning of the slide. Further destruction of infrastructure occurred when Hurricane Camille hit the Mississippi delta in 1969 causing a landslide which damaged several offshore drilling platforms.
Submarine landslides can pose a significant hazard when they cause a tsunami. Although a variety of different types of landslides can cause tsunami, all the resulting tsunami have similar features such as large run-ups close to the tsunami, but quicker attenuation compared to tsunami caused by earthquakes. An example of this was the July 17, 1998, Papua New Guinean landslide tsunami where waves up to 15 m high impacted a 20 km section of the coast killing 2,200 people, yet at greater distances the tsunami was not a major hazard. This is due to the comparatively small source area of most landslide tsunami (relative to the area affected by large earthquakes) which causes the generation of shorter wavelength waves. These waves are greatly affected by coastal amplification (which amplifies the local effect) and radial damping (which reduces the distal effect).
Recent findings show that the nature of a tsunami is dependent upon volume, velocity, initial acceleration, length and thickness of the contributing landslide. Volume and initial acceleration are the key factors which determine whether a landslide will form a tsunami. A sudden deceleration of the landslide may also result in larger waves. The length of the slide influences both the wavelength and the maximum wave height. Travel time or run out distance of slide will also influence the resulting tsunami wavelength. In most cases the submarine landslides are noticeably subcritical, that is the Frounde number (the ratio of slide speed to wave propagation) is significantly less than one. This suggests that the tsunami will move away from the wave generating slide preventing the buildup of the wave. Failures in shallow waters tend to produce larger tsunamis because the wave is more critical as the speed of propagation is less here. Furthermore, shallower waters are generally closer to the coast meaning that there is less radial damping by the time the tsunami reaches the shore. Conversely tsunamis triggered by earthquakes are more critical when the seabed displacement occurs in the deep ocean as the first wave (which is less affected by depth) has a shorter wavelength and is enlarged when travelling from deeper to shallower waters.
The effects of a submarine landslide on infrastructure can be costly and landslide generated tsunami can be both destructive and deadly.
Giant Slides along the Norwegian Margin
Storegga Slide is among the largest recent submarine landslides discovered worldwide. Like many other submarine landslides from the North Atlantic it is dated to a Pleistocene - Holocene age. Such large submarine landslides have been interpreted to occur most frequent either during the Northern Hemisphere Glaciation (NHG) or during the deglaciation, and. During those glacial or deglacial times a series of geological processes modified intensely the shallow structure of the submarine continental margin. For instance, changing sea levels during glaciation and accompanying sea level drop produce enhanced erosive processes. Advancing or retreating glaciers eroded the continent and provided vast amounts of sediment to the continental shelf. These processes led to the building of trough mouth fans, similar to river fan deltas. The large sediment accumulation promoted slope failures that are observed in the subsurface structure as stacked debris flows above each other. Sliding happened often along weak layers that have less shear strength due to higher effective internal pore pressures e.g. from gashydrate dissolution, other fluids, or simply weakening is due to contrasting sediment properties within the sediment succession. Earthquakes caused by isostatic rebound due to waning glacials are typically assumed as final land-sliding triggers.
In recent years, a series of giant Mass Transport Deposits (MTDs) that are volumetrically much bigger than the deposits of the Storegga slide have been detected in several locations in the subsurface geological record of the Norwegian continental margin using geophysical methods. These MTDs exceed in size any slope failure of the youngest high-glacial times. Individual deposits reach up to 1 km in thickness and the largest are up to 300 km in length. The internal structure imaged with seismic methods shows sometimes a transparent or a chaotic character indicating disintegration of the slide mass. In other examples, subparallel layering supports a cohesive sliding/slumping on a large scale. Local over-pressures are indicated by diapiric structures indicating gravity driven sub-vertical movement of water-rich sediment masses. Norway and Svalbard basins contain several of these giant MTDs, that span in age from Pliocene age at 2.7-2.3Ma to ~0.5 M.. In the Lofoten Basin  detected similar giant MTDs, but in this case all slides are younger than ~1 Ma. There is an ongoing debate on the generation of giant slides and their relation to Northern Hemisphere Glaciation.
The 1692 Jamaica earthquake struck Port Royal, Jamaica on 7 June. A stopped pocket watch found in the harbour in 1959 indicated that it occurred around 11:43 a.m.Known as the "storehouse and treasury of the West Indies", and as "one of the wickedest places on Earth", it was, at the time, the unofficial capital of Jamaica, one of the busiest and wealthiest ports in the West Indies, and a common home port for many of the privateers and pirates operating within the Caribbean Sea.
The earthquake caused most of the city to sink below sea level.
About 2,000 people died as a result of the earthquake and the following tsunami; and, about another 3,000 people died in the days following the earthquakes, due to injuries and disease.1918 San Fermín earthquake
The 1918 San Fermín earthquake, also known as the Puerto Rico earthquake of 1918, struck the island of Puerto Rico at 10:14:42 local time on October 11. The earthquake measured 7.1 on the moment magnitude scale and IX (Violent) on the Mercalli intensity scale. The mainshock epicenter occurred off the northwestern coast of the island, somewhere along the Puerto Rico Trench.
The earthquake triggered a tsunami with waves measured that swept the west coast of the island. The combined effects of the earthquake and tsunami made it one of the worst natural disasters that have struck the island. The losses resulting from the disaster were approximately 76–118 casualties and $4–29 million in property damage.1929 Grand Banks earthquake
The 1929 Grand Banks earthquake (also called the Laurentian Slope earthquake and the South Shore Disaster) occurred on November 18. The shock had a moment magnitude of 7.2 and a maximum Rossi–Forel intensity of VI (Strong tremor) and was centered in the Atlantic Ocean off the south coast of Newfoundland in the Laurentian Slope Seismic Zone.1953 Suva earthquake
The 1953 Suva earthquake occurred on 14 September at 00:26 UTC near Suva, Fiji, just off the southeast shore of Viti Levu. This earthquake had a magnitude of Ms 6.8. The earthquake triggered a coral reef platform collapse and a submarine landslide that caused a tsunami. Eight people were reported killed; a wharf, bridges, and buildings were severely damaged in Suva.1979 Nice tsunami
On October 16, 1979: a landslide at the Nice Airport, an aseismic submarine landslide, and two tsunamis that struck the coast near Nice.
The two waves struck the coast between the Italian border and the town of Antibes (60 miles; 96 km). They reached 3 m high near Nice and 3.5 m at La Salis (Antibes) and decreased in amplitude from there.Abyss Box
The Abyss Box is a vessel containing 16 litres (3.5 imp gal; 4.2 US gal) of water at the very high pressure of 18 megapascals to simulate the natural underwater environment of bathyal fauna living at about 1,800 metres (5,900 ft) below the surface. It is on display at Oceanopolis aquarium in Brest, France. It was designed by French researcher Bruce Shillito from Pierre and Marie Curie University in Paris.All the equipment maintaining the extreme pressure inside the Abyss Box weighs 600 kilograms (1,300 lb). The device keeps deep-dwelling creatures alive so they can be studied, especially regarding their adaptability to warmer ocean temperatures. Currently the Abyss Box houses only common species of deep sea creatures including a deep sea crab, Bythograea thermydron and a deep sea prawn, Pandalus borealis, which are some of the hardier species with a higher survival rate in depressurized environments.Cabot Strait
Cabot Strait (; French: détroit de Cabot, French: [kabo]) is a strait in eastern Canada approximately 110 kilometres wide between Cape Ray, Newfoundland and Cape North, Cape Breton Island. It is the widest of the three outlets for the Gulf of Saint Lawrence into the Atlantic Ocean, the others being the Strait of Belle Isle and Strait of Canso. It is named for the Genoese explorer Giovanni Caboto.The strait's bathymetry is varied, with the Laurentian Channel creating a deep trench through its centre, and comparatively shallow coastal waters closer to Newfoundland and Cape Breton Island. These bathymetric conditions have been known by mariners to cause rogue waves. The steep slope of the Laurentian Channel was the site of a disastrous submarine landslide at the southeastern end of the strait, triggered by the 1929 Grand Banks earthquake and leading to a tsunami that devastated communities along Newfoundland's south coast and parts of Cape Breton Island.A strategically important waterway throughout Canadian and Newfoundland history, the strait is also an important international shipping route, being the primary waterway linking the Atlantic with inland ports on the Great Lakes and St. Lawrence Seaway.
The strait is crossed daily by the Marine Atlantic ferry service linking Channel-Port aux Basques, and North Sydney. Ferries have been operating across the strait since 1898 and a submarine telegraph cable was laid in 1856 as part of the transatlantic telegraph cable project.An infamous location in the strait for shipwrecks during the age of sail, St. Paul's Island, came to be referred to as the "Graveyard of the Gulf" (of St. Lawrence).
In October 1942, German U-boat U-69 torpedoed and sank the unlit Newfoundland ferry SS Caribou, killing 137 people. Then on 25 November 1944 HMCS Shawinigan was torpedoed and sunk with all hands on board (91 crew) by U-1228.Deep sea
The deep sea or deep layer is the lowest layer in the ocean, existing below the thermocline and above the seabed, at a depth of 1000 fathoms (1800 m) or more. Little or no light penetrates this part of the ocean, and most of the organisms that live there rely for subsistence on falling organic matter produced in the photic zone. For this reason, scientists once assumed that life would be sparse in the deep ocean, but virtually every probe has revealed that, on the contrary, life is abundant in the deep ocean.
From the time of Pliny until the late nineteenth century...humans believed there was no life in the deep. It took a historic expedition in the ship Challenger between 1872 and 1876 to prove Pliny wrong; its deep-sea dredges and trawls brought up living things from all depths that could be reached. Yet even in the twentieth century scientists continued to imagine that life at great depth was insubstantial, or somehow inconsequential. The eternal dark, the almost inconceivable pressure, and the extreme cold that exist below one thousand meters were, they thought, so forbidding as to have all but extinguished life. The reverse is in fact true....(Below 200 meters) lies the largest habitat on earth.
In 1960, the Bathyscaphe Trieste descended to the bottom of the Mariana Trench near Guam, at 10,911 m (35,797 ft; 6.780 mi), the deepest known spot in any ocean. If Mount Everest (8,848 metres) were submerged there, its peak would be more than a mile beneath the surface. The Trieste was retired, and for a while the Japanese remote-operated vehicle (ROV) Kaikō was the only vessel capable of reaching this depth. It was lost at sea in 2003. In May and June 2009, the hybrid-ROV (HROV) Nereus returned to the Challenger Deep for a series of three dives to depths exceeding 10,900 meters.
It has been suggested that more is known about the Moon than the deepest parts of the ocean. Life on the deep ocean floor was assumed to rely solely on falling organic matter, and therefore ultimately the sun, for its energy source until the discovery of thriving colonies of shrimps and other organisms around hydrothermal vents in the late 1970s. The new discoveries revealed groups of creatures that obtained nutrients and energy directly from thermal sources and chemical reactions associated with changes to mineral deposits. These organisms thrive in completely lightless and anaerobic environments in highly saline water that may reach 300 °F (150 °C), drawing their sustenance from hydrogen sulfide, which is highly toxic to almost all terrestrial life. The revolutionary discovery that life can exist under these extreme conditions changed opinions about the chances of there being life elsewhere in the universe. Scientists now speculate that Europa, one of Jupiter's moons, may be able to support life beneath its icy surface, where there is evidence of a global ocean of liquid water.Doggerland
Doggerland was an area of land, now submerged beneath the southern North Sea, that connected Britain to continental Europe. It was flooded by rising sea levels around 6500–6200 BC. Geological surveys have suggested that it stretched from Britain's east coast to the Netherlands and the western coasts of Germany and the peninsula of Jutland. It was probably a rich habitat with human habitation in the Mesolithic period, although rising sea levels gradually reduced it to low-lying islands before its final submergence, possibly following a tsunami caused by the Storegga Slide.The archaeological potential of the area was first identified in the early 20th century, and interest intensified in 1931 when a fishing trawler operating east of the Wash dragged up a barbed antler point that was subsequently dated to a time when the area was tundra. Vessels have dragged up remains of mammoths, lions and other animals, and a few prehistoric tools and weapons.Doggerland was named in the 1990s, after the Dogger Bank, which in turn was named after the 17th century Dutch fishing boats called doggers.Hawaiian Trough
The Hawaiian Trough, otherwise known as the Hawaiian Deep, is a moat-like depression of the seafloor surrounding the Hawaiian Islands. The weight from the Volcanic Island chain depresses the plastic Lithosphere that is already weakened by the underlying thermal hotspot, causing subsidence to occur. The location with the greatest rate of subsidence is directly above the hotspot with a rate of about 2.5 millimeters per year. The Hawaiian Trough is about 5500 meters deep. The subsiding lithosphere is balanced out and through the concept of isostasy a part of the crust surrounding the trough is levered upwards creating the Hawaiian Arch. The Hawaiian Arch extends about 200 meters above the surrounding ocean floor, and contains tilted coral reefs.Kaikoura Peninsula
The Kaikoura Peninsula is located in the northeast of New Zealand's South Island. It protrudes five kilometres into the Pacific Ocean. The town of Kaikoura is located on the north shore of the peninsula. The peninsula has been settled by Maori for approximately 1000 years, and by Europeans since the 1800s, when whaling operations began off the Kaikoura Coast. Since the end of whaling in 1922 whales have been allowed to thrive and the region is now a popular whale watching destination.
The Kaikoura Peninsula is made up of limestone and mudstone which have been deposited, uplifted and deformed throughout the Quaternary. The peninsula is situated in a tectonically active region bounded by the Marlborough Fault System.
The Kaikoura Canyon is a submarine canyon situated 500 metres off the coast to the south-east of the peninsula. It is 60 km long, up to 1200 m deep, and is generally U-shaped. It is an active canyon that merges into a deep-ocean channel system that meanders for hundreds of kilometres across the deep ocean floor.Landslide
The term landslide or less frequently, landslip, refers to several forms of mass wasting that include a wide range of ground movements, such as rockfalls, deep-seated slope failures, mudflows, and debris flows. Landslides occur in a variety of environments, characterized by either steep or gentle slope gradients, from mountain ranges to coastal cliffs or even underwater, in which case they are called submarine landslides. Gravity is the primary driving force for a landslide to occur, but there are other factors affecting slope stability that produce specific conditions that make a slope prone to failure. In many cases, the landslide is triggered by a specific event (such as a heavy rainfall, an earthquake, a slope cut to build a road, and many others), although this is not always identifiable.List of tsunamis in Europe
The following is a list of notable tsunamis in Europe.Moruroa
Moruroa (Mururoa, Mururura), also historically known as Aopuni, is an atoll which forms part of the Tuamotu Archipelago in French Polynesia in the southern Pacific Ocean. It is located about 1,250 kilometres (780 mi) southeast of Tahiti. Administratively Moruroa Atoll is part of the commune of Tureia, which includes the atolls of Tureia, Fangataufa, Tematangi and Vanavana. France undertook nuclear weapon tests between 1966 and 1996 at Moruroa and Fangataufa, causing international protests, notably in 1974 and 1995. The number of tests performed has been variously reported as 175 and 181.Mudflow
A mudflow or mud flow is a form of mass wasting involving "very rapid to extremely rapid surging flow" of debris that has become partially or fully liquified by the addition of significant amounts of water to the source material.Mudflows contain a significant proportion of clay, which makes them more fluid than debris flows; thus, they are able to travel farther and across lower slope angles. Both types are generally mixtures of various kinds of materials of different sizes, which are typically sorted by size upon deposition.Mudflows are often called mudslides, a term applied indiscriminately by the mass media to a variety of mass wasting events. Mudflows often start as slides, becoming flows as water is entrained along the flow path; such events are often called flow slides.Other types of mudflows include lahars (involving fine-grained pyroclastic deposits on the flanks of volcanoes) and jökulhlaups (outbursts from under glaciers or icecaps).A statutory definition of "flood-related mudslide" appears in the United States' National Flood Insurance Act of 1968, as amended, codified at 42 USC Sections 4001 and following.Olistostrome
An olistostrome is a sedimentary deposit composed of a chaotic mass of heterogeneous material, such as blocks and mud, known as olistoliths, that accumulates as a semifluid body by submarine gravity sliding or slumping of the unconsolidated sediments. It is a mappable stratigraphic unit which lacks true bedding, but is intercalated amongst normal bedding sequences, as in the Cenozoic basin of central Sicily. The term olistostrome is derived from the Greek olistomai (to slide) and stroma (accumulation).Sponge ground
Sponge grounds, also known as sponge aggregations, are intertidal to deep-sea habitats formed by large accumulations of sponges (glass sponges and/or demosponges), often dominated by a few massive species. Sponge grounds were already reported more than 150 years ago, but the habitat was first fully recognized, studied and described in detail around the Faroe Islands during the inter-Nordic BIOFAR 1 programme 1987–90. These were called Ostur (meaning "cheese" and referring to the appearance of the sponges) by the local fishermen and this name has to some extent entered the scientific literature. Sponge grounds were later found elsewhere in the Northeast Atlantic and in the Northwest Atlantic, as well as near Antarctica. They are now known from many other places worldwide and recognized as key marine habitats.Sponge grounds are important habitats supporting diverse ecosystems. During a study of outer shelf and upper slope sponge grounds at the Faroe Islands, 242 invertebrate species were found in the vicinity and 115 were associated with the sponges. In general, fish fauna associated with sponge grounds are poorly known, but include rockfish and gadiforms. Sponge grounds are threatened, especially by bottom trawling and other fishing gear, dredging, oil and gas exploration and undersea cables, but potentially also by deep sea mining, carbon dioxide sequestration, pollution and climate change.Tuscaloosa seamount
The Tuscaloosa Seamount is an undersea mountain in the Hawaii archipelago. It is located about 100 kilometres (62 mi) northeast of the island O'ahu.
In contrast to the overwhelming majority of seamounts, the Tuscaloosa Seamount is not a submarine volcano. It is a huge block of rocks that broke off about two million years ago at the Nuuanu Giant Submarine Landslide of O'ahu when the volcano Koʻolau collapsed.The Tuscaloosa Seamount is 30 km (19 mi) long and 17 km (11 mi) wide. Its shallow summit rises 1.8 kilometres (1.1 mi) across the sea bottom but is 2,756 metres (9,042 ft) below the sea level.USS Monongahela (1862)
USS Monongahela (1862) was a barkentine–rigged screw sloop-of-war that served in the Union Navy during the American Civil War. Her task was to participate in the Union blockade of the Confederate States of America. Post-war, she continued serving her country in various roles, such as that of a storeship and schoolship.