Submarine landslide classification scheme ( Prior and Coleman, 1982).As can be seen in Fig. 6.7, submarine landslide has roughly two final destruction forms: one is the basically intact form after sliding subject stops sliding without crushing collapse; another is the sliding subject constantly moving along the slope, and the sliding subject calves into sediments flow (debris flow).The final morphological type of submarine landslide is decided by soil properties, topography and load energy, and other comprehensive factors. In order to conduct scientific classification for submarine landslides, we must make a comprehensive analysis of the above factors.With the development of critical state soil mechanics ( Roscoe and Burland, 1968; Wood, 1990), the steady-state theory of soil has been gradually accepted by people and applied to engineering practice.
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In recent years, the steady-state theory has been applied to marine soil investigation and research. It is mainly used for evaluating the actions of soil and sediment in large strain behavior; it is also used to evaluate the form of sediment movement after failure. Schwab and H.J. Lee (1988) and W.C.
Schwab et al. (1987) used steady-state theory to conduct the quantitative analysis and evaluation for landslide landform. (1989) evaluated the generation of landslide on submarine volcanic margin and slope and the form transformation from overall destruction to crushing destruction.
(1991), on the basis of previous work, summarized the use of steady-state theory in the quantitative evaluation of landslide evolution process.The steady-state deformation refers to the continuous deformation of soil under constant effective normal stress, constant shear stress, and constant shear strain rate. During deformation, the steady state can be achieved only when the soil structure is completely reshaped, and the influence of all grain orientation reaches a stable condition. In this way, the shear stress and strain rate can achieve constant. Steady state exists only in the deformation process. Under the drained and undrained conditions, all granular aggregates can reach the steady state ( Poulos, 1981). Generally speaking, it is believed that steady state depends only on void ratio e, so in void ratio and positive stress space, it can divide soil into dilative and shear shrinkage soil ( Fig. 6.8 for the landslide type corresponding to these two kinds of soil). Sediments with status a show shear shrinkage behavior; shear shrinkage soil has characteristics with continuous decrease of average effective stress, peak strength far greater than steady-state strength when preserved in large strain q ss.
Shear shrinkage soil in the shearing process trends to reducing size, so under the undrained condition, this will increase the pore water pressure and continuously decrease the shear strength, so that the steady-state strength is far below the peak shear strength S u. Effective stress path of sediments in two states ( Keyen et al., 1989).Sediments with state b show behavior from weak shrinkage to dilatancy, and dilative soil has the characteristic of continuous increase of partial stress.
Dilative soil has volume increasing trend in the shear process, so under undrained condition, it will cause the decrease of pore water pressure and continuous increase of shear strength, and this is so even in the case of large strain. Typically, steady-state shear strength of the sediment is greater than the slope shear stress of gravity, the movement along the slope only occurs when the external slope stress takes actions on the slope subject (such as earthquake); once the dynamic load or external static load disappear, deformation will stop, and soil will be in a stable state. The instability of soil's instantaneous state will lead to the overall slope (nonbroken) deformation and finally the moved block shape ( Schwab and Lee, 1988). Here the slope sometimes become steeper because of scouring effect, and at this time the shear stress along the slope may be close to or exceed the steady-state shear strength; this also can cause serious deformation and produce a permanent change ( Whitman, 1985). This failure movement form is called nondisintegrative failure.These two types of landslide division reflect the soil properties and terrain characteristics, also reflect the soil failure mechanism, and it belongs to a comprehensive classification method. In addition, dilative soil can also become disintegrative failures under special conditions, but it requires more energy and absorbs more water to make the dilative soil more resistant to external load.Submarine landslides can also be divided by the landslide scale. The landslide scale is determined by the size of landslide mass, but landslide body's volume changes greatly, from a few cubic meters or tens of cubic meters to tens of millions or even hundreds of millions of cubic meters.
In the description and evaluation of landslide scale, the following classification is often followed: ① very small: single block, small isolated block with volume of several cubic meters; ② small: from tens to 200 cubic meters; ③ medium: from hundreds to 2000 cubic meters; ④ large: from thousands to 2 million cubic meters; and ⑤ giant: more than 2 million cubic meters. Landslide scale is usually affected by topography and composition.
For example, the landslide that happened in tidal channel in eastern Zhejiang has limited development space and small scale because of the control of tidal channel terrain ( Fig. 6.9), whose the side slope height is small and landslide of small scale is accumulated at the bottom of tidal channel. Large-scale landslides often occur on continental slope, seamounts, and island slope because this kind of slope has enough space and material to form a large-scale landslide ( Embley and Jacobi, 1977) ( Fig. 6.10).
Aaron Micallef, in, 2011 AbstractSubmarine landslides constitute a geohazard to humans and their infrastructures. Recent studies, supported by the rapid advances in seafloor mapping technology, have shown that submarine landslides are important geological processes in terms of their widespread occurrence, their size and the volume of sediment they displace. Submarine mass movement processes are, however, poorly understood. The investigation of submarine landslides still presents a challenge to marine geomorphologists today because of their large scale and inaccessibility. The type of information on submarine landslides that is available to the marine geoscientist is generally morphological and acquired remotely. For these reasons, geomorphological mapping has become an important tool in the study of submarine landslides.In this chapter, I review the methods used by marine geomorphologists to generate geomorphological maps of submarine landslides, assess the characteristics of these maps and suggest ways in which they can be improved. I will also demonstrate the utility of geomorphological mapping in assessing the risk associated with an offshore gas field development and in improving our understanding of submarine landslide dynamics in the Storegga Slide off the Norwegian coast.
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Ye Yincan et al, in, 2017 1.2.1 Submarine LandslideSubmarine landslide refers to the process and phenomenon of rock or soil composing the submarine slope to slide down along the continuous failure face under the action of natural or human activities and other sudden factors. Submarine landslides often occur at the slope zone of the edge of the continental shelf that is vulnerable to crust tectonic activity, earthquake effect, or rapid deposition of coastal, estuarine delta, tidal channel, and harbor area. The Mississippi River delta of USA, Magdarena and Esmeraldas deltas of South America, Copper River delta of Alaska, and Fresse delta of Canada, they all have been founded the submarine landslides. They usually occur in the gradient of 1–4 degrees or smaller slope.Study of the main estuary submarine delta slope instability of China indicates that the development of submarine landslide is most typical in the Yellow River submarine delta region; the submarine landslide in this region is the superficial small landslide due to the wave and storm action. It is well developed on the middle and upper part of the Yellow River submarine slope. This kind of landslide is burst and a rapid geological or geomorphologic process, and repeats under the effects of periodic dynamic factors ( Yang and Shen, 1991, 1994 Yang and Shen, 1991 Yang and Shen, 1994).There are universal phenomena of submarine landslides in China's coastal areas and islands.
Studies show that channel-type deep-water harbor in island area has special geology, geomorphology, and hydrodynamic conditions, and its waterway center has fast speed flow, and it suffers from intense erosion, with bottom material of sand, gravel, and other coarse grain sediment, and channel slope; especially both sides of waterway have relatively slow flow, and is in a slow deposition environment, with bottom material of new soft soil deposit. This strong difference of rushing and siltation between channel center and both sides is easy easily forms the narrow and steep slope, which causes landslide under the external force action. Mienert, in, 2009 Natural Trigger Mechanisms of Slides from Geological RecordsMost submarine landslides occur unobserved on the seabed along continental margins. We, therefore, deduct the processes involved on the basis of seabed bathymetry, sub-seabed paleomorphology, and sediment cores a long time after an event takes place.
Only a very few submarine landslide events are directly documented. They caused submarine cable breaks or started as an underwater slope failure and retrogressively approached the coastline.
Much less information exists about their trigger mechanisms, and the most widely used example for a continental slope failure is the 1929 Grand Banks earthquake. It appeared to trigger a slump that subsequently developed into a turbidity current.Another condition that is most commonly associated with submarine slides is the rapid accumulation of thick sedimentary deposits over under-consolidated sediments, which by generating excess pore pressure reduces the effective stress that holds the sediment grains together. The magnitude of a combined instantaneous loading and a progressive excess pore pressure buildup appear to generate weakened sediment layers. The resulting reduction in shear strength allows sediments to move down very gentle slopes (. Hickey, in, 2015 4.3.2.1 GenerationThree substantial submarine landslides took place between 30,000 and 7,200–7,000 years BP in the Norwegian Sea on the northern edge of the Atlantic Ocean.
These slides are cumulatively referred to as the Storegga Slides. These events were most likely caused by isostatic uplift west of Norway in an area that is away from plate boundaries, and therefore considered tectonically inactive. It is probable that continental slopes were steepening from increased land-based erosion causing large volumes of sediment to deposit in this area.
It is unknown how long this sediment took to accumulate and whether it was over one or multiple glacial cycles. The denudation rates increased during the Quaternary when extensive ice sheets periodically developed and retreated on these uplifted areas ( Long and Holmes, 2001). Sediment delivery to the continental shelf is only possible when the coastal waters and adjoining lands are not covered by permanent ice and it is only during glacial retreat and ice melt could this magnitude of sediment erosion could take place. The massive sediment erosion and subsequent deposition eventually resulted in large-scale submarine landslides. This slope failure could have been triggered by small earthquakes related to the isostatic uplift. Three exceptionally large submarine landslides have been mapped on the sea floor.
It is likely that all three generated tsunamis (Dawson et al., 1998). (10) γ 0 = τ y a μ l − μ h.For these nonlinear rheologies, the no-slip boundary condition along the base of the debris flow results in two flow zones: a shear zone at the base of the flow where the shear stress is greater than the yield stress and a plug zone above where the yield stress is not exceeded. The boundary between the two zones is termed the yield interface. In formulating a solution to the momentum equations, the horizontal and vertical velocities and the horizontal velocity gradient are constrained to be continuous across the yield interface ( Jiang and Leblond, 1993). Dr.Antony Joseph, in, 2011 2.2 Tsunamis Generated by Surface/Submarine Landslides and Rock AvalanchesLocal offshore or onshore earthquakes produce landslides (submarine or surface), although landslides do not always require an earthquake to trigger them.
The December 2004 Sumatra-Andaman earthquake of magnitude 9.3 generated a 30-meter-high tsunami following the occurrence of a 15-meter slip of the ocean floor along a 1300-km-long and 160- to 240-km-wide rupture. The tsunami power was enhanced by large landslides (several kilometers across) over the rupture zone of this earthquake. The force of the displaced water was such that blocks of rocks, weighing millions of tons, were dragged as much as 10 km. An oceanic trench several km wide was also formed (Rastogi, 2007).Large “impulse type” (short duration) surface/ submarine landslides (or episodes of several discrete events) have generated tsunamis. Although a submarine landslide or a subaerial landslide that flows into a large body of water can cause a tsunami, surface landslides are much more effective tsunami generators than the slower submarine landslides. It has been observed that submarine landslides generate tsunamis only when the volume of the material moved is substantial and moves at a great speed.
The characteristics of these tsunamis are different from those of earthquake-generated tsunamis, which displace seabeds. In some cases, landslides are triggered by earthquakes. For example, the Grand Banks landslide-generated tsunami of November 18, 1929, was triggered by a M = 7.2 earthquake that occurred at the southern edge of the Grand Banks, located 280 km south of Newfoundland, at an estimated depth of 20 km beneath the seafloor (Fine et al., 2005; Clague, 2001). The earthquake triggered a large submarine slope failure (200 km 3), which was transformed into a turbidity current carrying mud and sand up to 1000 km at estimated speeds of 60–100 km/h, breaking 12 telegraph cables.
The tsunami generated by this failure killed 28 people, making it the most catastrophic tsunami in Canadian history. Tsunami waves also were observed along other parts of the Atlantic coast of Canada and the United States. Waves crossing the Atlantic ( Figure 2.4) were recorded on the coasts of Portugal and the Azores Islands.
These tsunami waves had amplitudes of 3–8 meters. Source and propagation of the 1929 Grand Banks landslide-generated tsunami waves in the North Atlantic Ocean. Source: Fine et al., 2005; Reproduced with kind permission of Elsevier.In contrast to rigid landslides, which move as single, consolidated bodies, preserving their size and form, viscous slides normally spread and flatten as they move downslope. The concentrated and focused moving-slide mass (similar to snow/ice avalanches in mountains) was apparently the main reason for the numerous cable breaks.The African coast is also subject to local landslide-generated tsunamis that can occur near any part of the coastline, especially areas that are near the mouths of large African rivers. In fact, historical chronicles abound of several instances of unusual wave run-ups observed in the area near the Gulf of Guinea, off central West Africa. It has been suggested that in many cases of tsunamis accompanied by seaquakes in tropical countries, the tsunamis are not only induced directly by the seaquakes but are also spurred by submarine landslides (i.e., submarine slope sliding triggered by the earthquake shaking).
An example of such a tsunami is one that occurred in the sea area north of Aitape City on the northern coast of Papua New Guinea in the wake of the June 15, 1998, earthquake of magnitude 7.0, during which seawater rose 15 meters above the mean sea level and more than 2000 people perished. It was pointed out that a huge submarine landslide was induced by the main shock, and the main part of the tsunami was generated by the landslide and not by the seaquake itself. In this case, the secondary tsunami was larger than the first tsunami, which was caused by the crustal motion of the sea bed (Tsuji, 2009). There had been instances where large tsunamis were generated by rock avalanches, which is a geodynamic phenomenon. For example, the First Nations (Da'naxda'xw) village of Kwalate, Knight Inlet, British Columbia, Canada ( Figure 2.5), was completely swept away by a 2- to 6-meter-high tsunami that formed when an 840-meter-high, 30 × 10 6 m 3 subaerial rock avalanche ( Figures 2.6 and 2.7) descended into the water on the opposite side of the fjord in the mid-nineteenth century (Bornhold et al., 2007). The devastating rock avalanche and associated tsunami destroyed a large aboriginal community and forever altered the history of First Nations peoples.
Tappin, in, 2020 AbstractIn July 1998 an earthquake-triggered submarine landslide, located off the north coast of Papua New Guinea, generated a devastating tsunami which killed over 2200 people. The landslide, with the architecture of a slump, traveled 800 m downslope. During this movement internal deformation resulted in the rupturing of authigenic carbonate layers at the seabed, and the expulsion of methanogenic fluids that resulted in a proliferation of chemosynthetic communities.
The communities included Bathymodiolus, Calyptogena, and tube worms ( Lamellibrachia sp.). Here we describe these communities, their genesis, and the significance of the event. Gerassimos Papadopoulos, in, 2016 4.2.1.4 Marmara SeaIn the Marmara Sea it is likely that the predominant tsunami generation mechanism is the earthquake activity and associated coastal and submarine landslides ( Yalciner et al., 2002; Minoura et al., 2005). A characteristic example is the M7.9 earthquake of AD December 26, 1939, which ruptured a long segment of the North Anatolian Fault at a distance of ∼100 km inland from the Turkish Black Sea coast.
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After this very large earthquake a tsunami was observed in Black Sea coastal localities offshore north Turkey. The wave was recorded by Soviet tide gauges in the eastern Black Sea. A solution regarding the generation mechanism is the one which involves coseismic landsliding at the continental slope of the Black Sea between Sinop and Batumi ( Papadopoulos et al., 2011). One may suggest that a secondary fault was activated with the main earthquake. However, seismic records do not support the case, although we should take into account that the seismograph coverage of the area was very poor. Submarine landslide zone distribution map ( Feng et al., 1994a,b Feng et al., 1994a Feng et al., 1994b).According to Feng et al.
(1994a,b) Feng et al. (1994a) Feng et al. (1994b), the reason for landslide is that the submarine topography slopes of continental shelf outer edge and upper continental slope of northern South China Sea are large, and the bottom soil characteristics are very unstable, so huge submarine landslide zone develops.
Landslide zone has NE–SW direction zonal arrangement along the continental shelf outer edge break line; their position is closely related with left delta front continental slope, ancient coastline scarp, continental shelf outer edge break and upper continental slope geomorphology types. We have done a comparative analysis on the active fault, submarine landslide, and topography of South China Sea, and found that the submarine landslide belt and topography turning belt have close relationship with the submarine active fault zone; especially the inducing factors of submarine earthquake force should not be ignored. The research on submarine landslide is very important for the offshore oil and gas resources exploration and development, submarine pipeline engineering site selection, design, and implementation. Submarine landslide can be divided into early landslide and recent landslide; early landslides are all buried below the seabed, and usually they can be identified by single channel seismic and shallow stratigraphic profile survey. The recent landslides are distributed on today's seabed, which has direct meaning to the submarine engineering geologic work; its investigation methods use the side scan sonar or shallow stratum profile ( Fig. 4.18).
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