education

2006-09-18T10:14:00.000-07:00

Megatsunami threats

Volcanic islands (such as Réunion and the Hawaiian Islands) can cause megatsunamis to hit other nearby islands in the same chain because often they are structurally little more than large, unstable piles of loosely aggregated material heaped up by successive eruptions. Evidence for large landslides has been found in the form of extensive underwater debris aprons around them composed of the material which has slipped into the ocean. In recent years five such debris aprons have been found in the Hawaiian Islands alone.Some geologists speculate that the most likely candidate for the source of the next large-scale megatsunami is the island of La Palma, in the Canary Islands. During the 1949 eruption the western half of the Cumbre Vieja ridge slipped four metres downwards into the Atlantic Ocean. It is believed that this process was driven by the pressure caused by the rising magma heating and vaporising water trapped within the structure of the island, causing the island's structure to be pushed apart. The island is still considered active, though quiescent at present, but it is expected to erupt again some time in the next few thousand years. Were this to happen it is speculated that a megatsunami would be created as the western half of the island, weighing perhaps 500 billion tonnes, catastrophically slides into the ocean in a single event, causing local wave heights of hundreds of metres and a likely height of around 10–25 m at the Caribbean and the Eastern North American seaboard coast several hours later. However, this is speculative since there is disagreement whether it would in fact happen, when, or how likely it is.There is also disagreement amongst scientists as to if an eruption of Cumbre Vieja would cause a single large landslide (or a series of smaller landslides) and even if such a landslide would generate a tsunami capable of crossing the Atlantic. The Tsunami Society issued a statement in 2003 that such collapses are rare and occur at intervals of thousands or millions of years, that the risk of La Palma collapsing was over-dramatized, and that although the catastrophic collapse of the islands of Krakatoa and Santorini produced megatsunamis in the local region, huge waves did not propagate across oceans to cause similar devastation on more distant coasts, adding that evidence (including computer simulations and experiments with models) suggests this type of wave does not travel great distances in the same way that normal tsunamis do. Besides fjords in Alaska, many locations face threats of localized, but still potentially dangerous, megatsunami-type waves. Some geologists speculate that an unstable rock face at Mount Breakenridge above the north end of the giant fresh-water fjord of Harrison Lake in the Fraser Valley in southwestern British Columbia could collapse into the lake, generating a large wave that might destroy the town of Harrison Hot Springs at the south end

2006-09-18T10:10:00.000-07:00

MEGATSUNAMI

Megatsunami (often hyphenated as mega-tsunami, also known as iminami or "wave of purification") is an informal term used by popular media and popular science to describe a very large tsunami-like wave significantly beyond the size reached by tsunamis (typically around 10 meters). For this reason, there is no scientific definition of a megatsunami. Informally, the term generally refers to waves beyond the norm for tsunamis, ranging from over 40 metres (131 feet) to giants over 100 metres (328 feet) tall. Note that megatsunamis often reach higher than their wave height when they meet land, as the water often floods upwards from the force of impact.
Megatsunamis are related to tsunamis in name only: they do not usually have the same cause or appearance, the only connection being that both are very large scale water movements caused by point events. They are also not the same as freak waves which appear in ocean waters and are often up to 30 meters tall.Unlike tsunamis, which are primarily due to seismic activity in the earth's crust raising or lowering the sea bed by a few meters over a large area, megatsunamis are caused by a very large impact or landslide into a body of water when the water cannot disperse in all directions. For this reason, they are usually a highly localized effect, either occurring when the origin of a tsunami is extremely close to the shore, or in deep, narrow inlets, lakes or other water passages.

2006-09-18T10:06:00.000-07:00

Warning and prevention

Tsunamis cannot be prevented or precisely predicted, but there are some warning signs of an impending tsunami, and there are many systems being developed and in use to reduce the damage from tsunamis.
In instances where the leading edge of the tsunami wave is its trough, the sea will recede from the coast half of the wave's period before the wave's arrival. If the slope is shallow, this recession can exceed many hundreds of metres. People unaware of the danger may remain at the shore due to curiosity, or for collecting fish from the exposed sea bed.

Tsunami warning sign on seawall in Kamakura, Japan, 2004. In the Muromachi period, a tsunami struck Kamakura, destroying the wooden building that housed the colossal statue of Amida Buddha at Kotokuin. Since that time, the statue has been outdoors.
In instances where the leading edge of the tsunami is its first peak, succeeding waves can lead to further flooding. Again, being educated about a tsunami is important, to realize that when the water level drops the first time, the danger is not yet over. In a low-lying coastal area, a strong earthquake is a major warning sign that a tsunami may be produced.
Regions with a high risk of tsunamis may use tsunami warning systems to detect tsunamis and warn the general population before the wave reaches land. In some communities on the west coast of the United States, which is prone to Pacific Ocean tsunamis, warning signs advise people where to run in the event of an incoming tsunami. Computer models can roughly predict tsunami arrival and impact based on information about the event that triggered it and the shape of the seafloor (bathymetry) and coastal land (topography).[3]
One of the early warnings comes from nearby animals. Many animals sense danger and flee to higher ground before the water arrives. The Lisbon quake is the first documented case of such a phenomenon in Europe. The phenomenon was also noted in Sri Lanka in the 2004 Indian Ocean earthquake ([4]). Some scientists speculate that animals may have an ability to sense subsonic Rayleigh waves from an earthquake minutes or hours before a tsunami strikes shore (Kenneally, [5]).
While it is not possible to prevent a tsunami, in some particularly tsunami-prone countries some measures have been taken to reduce the damage caused on shore. Japan has implemented an extensive programme of building tsunami walls of up to 4.5 m (13.5 ft) high in front of populated coastal areas. Other localities have built floodgates and channels to redirect the water from incoming tsunamis. However, their effectiveness has been questioned, as tsunamis are often higher than the barriers. For instance, the tsunami which hit the island of Hokkaido on July 12, 1993 created waves as much as 30 m (100 ft) tall - as high as a 10-story building. The port town of Aonae was completely surrounded by a tsunami wall, but the waves washed right over the wall and destroyed all the wood-framed structures in the area. The wall may have succeeded in slowing down and moderating the height of the tsunami but it did not prevent major destruction and loss of life.
The effects of a tsunami can be mitigated by natural factors such as tree cover on the shoreline. Some locations in the path of the 2004 Indian Ocean tsunami escaped almost unscathed as a result of the tsunami's energy being sapped by a belt of trees such as coconut palms and mangroves. In one striking example, the village of Naluvedapathy in India's Tamil Nadu region suffered minimal damage and few deaths as the wave broke up on a forest of 80,244 trees planted along the shoreline in 2002 in a bid to enter the Guinness Book of Records. [6] Environmentalists have suggested tree planting along stretches of sea coast which are prone to tsunami risks. While it would take some years for the trees to grow to a useful size, such plantations could offer a much cheaper and longer-lasting means of tsunami mitigation than the costly and environmentally destructive method of erecting artificial barriers.

2006-09-18T09:51:00.000-07:00

Tsunami

Tsunamis can be generated when the sea floor abruptly deforms and vertically displaces the overlying water. Such large vertical movements of the Earth’s crust can occur at plate boundaries. Subduction earthquakes are particularly effective in generating tsunamis. As an Oceanic Plate is subducted beneath a Continental Plate, it sometimes brings down the lip of the Continental with it. Eventually, too much stress is put on the lip and it snaps back, sending shockwaves through the Earth’s crust, causing a tremor under the sea, known as an Undersea Earthquake.
Sub-marine landslides (which are sometimes triggered by large earthquakes) as well as collapses of volcanic edifices may also disturb the overlying water column as sediment and rocks slide downslope and are redistributed across the sea floor. Similarly, a violent submarine volcanic eruption can uplift the water column and form a tsunami.
Waves are formed as the displaced water mass moves under the influence of gravity and radiate across the ocean like ripples on a pond.In the 1950s it was discovered that larger tsunamis than previously believed possible could be caused by landslides, explosive volcanic action and impact events. These phenomena rapidly displace large volumes of water, as energy from falling debris or expansion is transferred to the water into which the debris falls. Tsunamis caused by these mechanisms, unlike the ocean-wide tsunamis caused by some earthquakes, generally dissipate quickly and rarely affect coastlines distant from the source due to the small area of sea affected. These events can give rise to much larger local shock waves (solitons), such as the landslide at the head of Lituya Bay which produced a water wave estimated at 50 – 150 m and reached 524 m up local mountains. However, an extremely large landslide could generate a megatsunami that might have ocean-wide impacts.

2006-09-17T00:47:00.000-07:00

Finite element method (FEM) is a powerful technique originally developed for numerical solution of complex problems in structural mechanics, and it remains the method of choice for complex systems. In the FEM, the structural system is modeled by a set of appropriate finite elements, which may have physical properties such as thickness, coefficient of thermal expansion, density, Young's modulus, shear modulus and Poisson's ratio. Some common element types are listed below:
Straight or curved one-dimensional elements endowed with physical properties such as axial, bending, and torsional stiffnesses. This type of elements is suitable for modeling cables, braces, trusses, beams, stiffeners, grids and frames. Straight elements usually have two nodes, one at each end, while curved elements will need at least three nodes including the end-nodes. The elements are positioned at the centroidal axis of the actual members.
Two-dimensional elements for membrane action (plane stress, plane strain) and/or bending action (plates and shells). They may have a variety of shapes such as flat or curved triangles and quadrilaterals. Nodes are usually placed at the element corners and, if needed for higher accuracy, additional nodes can be placed along the element edges or even inside the element. The elements are positioned at the mid-surface of the actual layer thickness.
Torus-shaped elements for axisymmetric problems such as thin, thick plates, shells, and solids. The cross-section of the elements are similar to the previously described types: one-dimensional for thin plates and shells, and two-dimensional for solids, and thick plates and shells.
Three-dimensional elements for modeling 3-D solids such as machine components, dams, embankments or soil masses. Common element shapes include tetrahedrals and hexahedrals. Nodes are placed at the vertexes and possibly in the element faces or within the element. The elements are interconnected only at the exterior nodes, and altogether they should cover the entire domain as accurately as possible. Nodes will have nodal displacements or degrees of freedom which may include translations, rotations, and for special applications, higher order derivatives of displacements. When the nodes displace, they will drag the elements along in a certain manner dictated by the element formulation. In other words, displacements of any points in the element will be interpolated from the nodal displacements, and this is the main reason for the approximate nature of the solution

2006-09-16T20:30:00.000-07:00

Prior to becoming a practicing engineer, civil engineers generally complete tertiary (college or higher) educational requirements, followed by several years of practical experience. Each country, state, or province individually regulates civil engineering practice:In the U.S., one must become a licensed Professional Engineer to do any civil engineering work affecting the public or to legally represent oneself as a civil engineer. Licensure requirements vary slightly by state, but in all cases entail passing two licensure exams, the Fundamentals of Engineering exam and the Principles and Practice exam (commonly called the PE), and completing a state-mandated number of years of work under the supervision of a licensed Professional Engineer. In addition, an educational requirement must often be met. All states accept a four year Bachelor of Science (BS) or Bachelor of Engineering (BEng) degree in Civil Engineering, from an ABET-accredited program, for their educational requirement. The acceptability of degrees in other fields varies by state; some states allow a person to substitute additional years of supervised work experience for the degree requirement. Although the American Society of Civil Engineers encourages states to raise the educational requirement to a graduate degree, advanced degrees are currently optional for civil engineers in the United States. Graduate study may lead either to a Master of Engineering, which is a Professional Master's degree, or to a Master of Science degree followed by a PhD in civil engineering or a sub-discipline.Texas A&M University in College Station, Texas, has the largest civil engineering department in the U.S. (2006) with 1,081 undergraduate students enrolled in that major alone. This does not include the 125 Texas A&M undergraduates majoring in ocean engineering, which overlaps heavily with (and descended from) civil engineering.In the United Kingdom current graduates require a MSc, MEng or BEng (Hons) in order to become chartered through the Institution of Civil Engineers. The Institution also allows entrants with substantial experience to apply without this level of formal academic achievement. In practice, most civil engineers in the United Kingdom work without chartered status. Unlike in many other European countries, the term 'Engineer' is not legally protected within the United Kingdom.

2006-09-16T20:18:00.000-07:00

Civil Engineering

In modern usage, civil engineering is a broad field of engineering that deals with the planning, construction, and maintenance of fixed structures, or public works, as they are related to earth, water, or civilization and their processes. Most civil engineering today deals with power plants, bridges, roads, railways, structures, water supply, irrigation, environment, sewer, flood control and traffic. In essence, civil engineering may be regarded as the profession that makes the world a more agreeable place in which to live.
Engineering has developed from observations of the ways natural and constructed systems react and from the development of empirical equations that provide bases for design. Civil engineering is the broadest of the engineering fields, partly because it is the oldest of all engineering fields. In fact, engineering was once divided into only two fields - military and civil. Civil engineering is still an umbrella term, comprised of many related specialities.

2006-09-16T18:48:00.000-07:00

Definition

Education is the process by which an individual is encouraged and enabled to develop fully his or her innate potential; it may also serve the purpose of equipping the individual with what is necessary to be a productive member of society. Through teaching and learning the individual acquires and develops knowledge, beliefs, and skills.