MEGA TSUNAMI - Wave Of Destruction

naen

bumi ni .. makin tua ..
makin lama, kita bleh nampak makin banyak bencana alam yg jadi kat sana sini
ngan ribut topannya .. ngan banjirnya .. gempa bumi, gunung berapi, dll ..
term yg paling feymes sejak beberapa tahun kebelakangan ni - global warming

tapi .. semua tu boleh dikirakan ancaman yg "kecik" je
errr besar sebenarnya .. cuma kemusnahan/korban yg terlibat dalam kejadian2 tu,
masih boleh dikatakan sebagai 'biasa' ataupun 'lumrah alam'
(kecuali kejadian tsunami 2004 & gempa bumi sichuan 2008)
dan global warming pun - kesannya adalah jangkamasa panjang, bukannya serta merta
macam kebanyakan bencana2 alam yg lain ..

kalau ada yg perasan, kadang2 tu kat mass media (terutamanya tv & internet),
ada mention pasal bencana besar yg bakal melanda kita pada masa akan datang
banyak teori yg dibentangkan - semuanya dikatakan "hari kemusnahan bumi" ..
antara yg dapat liputan meluas ialah tentang ombak besar - MEGA TSUNAMI ..

dikatakan bakal terjadi - mungkin dalam abad 21 ni, ataupun abad ke 22
dan kawasan yg bakal musnah ialah - pantai timur USA ..

sblom bukak citer pasal MEGA TSUNAMI ni, moh kita rewind balik (sikit) fakta TSUNAMI 2004 -

26 December 2004 : Tsunami & Facts - Indonesia

On December 26, 2004, a magnitude 9.0 earthquake occurred with an epicentre off the west coast of Northern Sumatra.

The earthquake generated two tsunami waves that slammed into the coast line of the northern Sumatera province of Aceh, minutes after the quake was generated.

The tsunami itself was generated along the 1200km fault rupture and the waves were recorded over 5,000 miles from the source.

The waves were reported to have travelled in the open ocean up to 600 miles per hour and each had a length, from the front of the wave to the back, of 100 kilometres.

The first wave gained height once reaching the coast line of Aceh and averaged a height of 3-4 meters and travelled inland for distance up to 2 kilometres.

Shortly after the first wave retreated, the second and more devastating wave arrived, which coastal evidence and local recollections have indicated had wave heights of between 10 and 15 metres and land infiltration to 8 kilometres inland.

A total of 110 bridges were destroyed, 5 seaports and 2 airports sustained considerable damage, and 82% of all roads were severy damaged.

baca bahagian yg merah tu, dan cuba bayangkan -
sesuatu yg berpuluh atau beratus kali ganda daripadanya .. itulah MEGA TSUNAMI ..

meremang tak? huhuhu .. moh baca lagi apa yg aku dapat kumpulkan ..

[ Last edited by  naen at 16-11-2008 11:06 PM ]

naen

MEGA TSUNAMI (also known as iminami or "wave of purification" ) is an informal term to indicate a tsunami that has initial wave heights that are much larger than normal tsunami. Unlike usual tsunamis, which originate from tectonic activity and the raising or lowering of the sea floor, most known mega tsunamis have originated from large scale impact events such as landslides, devastating volcanic eruptions, or meteor impacts.

A mega tsunami is meant to refer to a tsunami with an initial wave amplitude (wave height) measured in several tens, hundreds or possibly thousands of metres.

Normal tsunamis generated at sea have a small wave height offshore, and a very long wavelength (often hundreds of kilometers long). They generally pass unnoticed at sea, forming only a slight swell usually of the order of 30 cm above the normal sea surface. When they reach land the wave height increases dramatically as the base of the wave pushes the water column above it upwards.

Because megatsunamis are defined as beginning with a high wave height, all historically known tsunamis awarded the megatsunami designation have originated very close to the shore, or in deep, narrow inlets, lakes or other water passages where the water had few options for dispersal.

Megatsunamis may be caused by landslide and rockfall phenomena, explosive volcanic events, or asteroid impacts. Underwater earthquakes do not normally generate such large tsunamis, but landslides next to bodies of water resulting from earthquakes do, since they cause a massive amount of displacement.

LIST OF MEGA TSUNAMIS

PREHISTORIC

# The asteroid which created the Chicxulub Crater in Yucatan approximately 65 million years BP may have generated the largest megatsunami in the geological record.

# A giant tsunami may have been generated by the bolide impact that created the Chesapeake Bay impact crater, about 35.5 million years BP.

# At Seton Portage, British Columbia, Canada, a freshwater megatsunami may have occurred approximately 10,000 BP. A huge block of the Cayoosh Range suddenly slid northwards into what had been a large lake spanning the area from Lillooet, British Columbia to near Birken, in the Gates Valley or Pemberton Pass to the southwest. The event has not been studied in detail, but the proto-lake (freshwater fjord) may have been at least as deep as the two present-day halves, Seton and Anderson Lakes, which is to say of unknown depth, on either side of the Portage, suggesting that the surge generated by the giant landslide in the narrow mountain confines of the fjord valley may have been comparable in scale to Lituya Bay. Another more recent landslide on the south shore of Anderson Lake dropped a large portion of high mountainside down a debris chut, creating a rockwall "fan" which cannot not have made a megatsunami-type wave, though not as large as the main one at the Portage.

# 8000 years BP, a massive volcanic landslide off of Mt. Etna, Sicily caused a megatsunami which devastated the eastern Mediterranean coastline on three continents.

# In the Norwegian Sea, the Storegga Slide caused a megatsunami approximately 7,000 years BP.
# Approximately 4,000 BP, a landslide on R閡nion island, to the east of Madagascar, may have caused a megatsunami.

# Evidence for large landslides has been found in the form of extensive underwater debris aprons around many volcanic ocean islands which are composed of the material which has slid into the ocean. In recent years, five such debris aprons have been located around the Hawaiian Islands. The Canary Islands have at least 14 such debris aprons associated with the archipelago.

HISTORIC

# When the island of Santorini collapsed during its cataclysmic eruption approximately 3,615 BP (1615 BC), it produced a wave that surged to an estimated 100-150 metres and devastated much of the north coast of Crete after travelling 70 kilometres. However, this may not count as a megatsunami because the initial wave height was not as high.

# 40 metre high waves were generated by the collapse of Krakatau during its eruption in 1883 which killed 36,000 people on Java, Sumatra and the small islands around them.

RECENT

# Lituya Bay Tsunami

On 9 July 1958, a landslide at the head of Lituya Bay in Alaska, caused by an earthquake, generated a wave with an initial amplitude of 524m (1720 ft). The resultant megatsunami surged over the headland opposite, stripping trees and soil down to bedrock, and surged along the fjord which forms Lituya Bay, destroying a fishing boat anchored there and killing two people.

# Vajont Dam Tsunami

On 9 October 1963, a landslide above Vajont Dam in Italy produced a 250m (820 ft) megatsunami that overtopped the dam and destroyed the villages of Longarone, Pirago, Rivalta, Villanova and Fa

naen

NARRATOR (EMMA FIELDING): 40 million people live and work along the east coast of the United States, yet this entire population unknowingly lives under threat of a sudden catastrophe.

DR. SIMON DAY (Benfield Greig Hazard Research Centre, UCL): The east coast of America is, is the worst place this could happen. It抯 not some remote, deserted coastline, it抯 one of the most densely populated places in the world.

NARRATOR: Scientists have now found evidence that a colossal wave will one day devastate the coast of America. It will be far bigger than any normal tidal waves, or tsunami. It is what scientists call a mega-tsunami.

PROF. BILL McGUIRE (Benfield Greig Hazard Research Centre, UCL): It抯 almost inconceivable how much damage this event will cause and yet the general public knows absolutely nothing about it.

DR. GEORGE PLAFKER (US Geological Survey): These forces have almost unlimited power to cause utter destruction and there抯 nothing that we can do to stop them.

NARRATOR: Geologist George Plafker first came to this remote bay in southern Alaska 50 years ago. What he discovered were signs that a strange force of nature had once struck here.

GEORGE PLAFKER: Lituya Bay is one of my favourite places in the world. It抯 a magnificent landscape. There抮e mountains roaring up behind it, glaciers come off those peaks right down to sea-level and you have a bay that is unique along this coast.

NARRATOR: Plafker came to Lituya Bay with his colleague, Don Miller, in 1953. They came to survey for oil.

GEORGE PLAFKER: We didn抰 find any petroleum in Lituya Bay but what we did find was something that happened on a cataclysmic scale and we spent a large part of our time trying to understand it.

NARRATOR: What these scientists discovered in the 50s was the evidence for a previously unknown force of destruction. The evidence lay not in the rocks but in the trees.

GEORGE PLAFKER: One thing that was very peculiar is the fact that mature forest did not extend all the way down to the shoreline as was true almost everywhere else in this general area. Instead there were bands of younger trees below mature forest and the line at which the trees of different ages joined we call the trim line.

NARRATOR: Nothing like this had been recorded before. They suspected the surviving trees from just above the trim line might contain evidence of what had happened many years earlier.

GEORGE PLAFKER: We cut selected trees, took samples from those slices and sent them to the Juneau Forestry Research Lab and asked them to count the rings and give us an analysis of just what happened to those trees.

ELLEN ANDERSON (Juneau Forestry Sciences Lab, Alaska): This is a photo of a section of a spruce tree that was taken by Don Miller and George Plafker in 1953 in Lituya Bay. The tree was right above a trim line in the bay and it tells a very interesting story. The early growth in this tree was very good, nice wide rings. All of a sudden it changes. Something happened to it, something must have hit it very hard on this side over here. There抯 a large scar.

NARRATOR: The tree ring analysis showed a violent force had struck the entire shoreline of the bay. The forest looked like it had been hit by a giant wave. For the scientists it seemed impossible. No wave in history had ever reached anything like this high.

GEORGE PLAFKER: There was some powerful force at work here that created a wave possibly 150 metres high. That抯 the equivalent of say the height of a 50 storey building and we just didn抰 have any idea of what could do that.

NARRATOR: Even the most powerful waves, tidal waves, known to science by their Japanese name tsunami, could not have created such destruction. This wave had been caused by something very different.

GEORGE PLAFKER: Well we didn抰 know what caused the wave. We considered earthquakes and earthquakes cause tsunami but those tsunamis are usually less than 10-15 metres and here we have something that抯 10 times as high as that.

NARRATOR: In comparison one of the most destructive tsunami this century hit the islands of Hawaii in 1946 destroying the town of Hilo yet it was little more than 10 metres high. Waves surged far inland causing death and destruction before petering out in the town. Like almost all tsunami the wave that struck Hilo was created by an earthquake on the ocean floor far away.

PROF. GARY McMURTRY (University of Hawaii): Well the Hilo tsunami in 1946, the classic earthquake generated tsunami, came from thousands of kilometres away. There was no warning, very little warning at all and destroyed large portions of the city and over 100 people were killed, including quite a few children.

NARRATOR: It is known that for all their destructiveness tsunami formed by earthquakes are inherently limited in size. That is because they are caused by shifts in the seabed. When an earth-quake cracks the ocean floor one side of the fracture rises up. When this happens the water above the fracture is lifted up by the same amount. This movement pushes the water upwards and outwards creating a wave on the surface of the sea which becomes a tsunami, but even the biggest earthquakes can only lift the sea floor by about 10 metres which creates a wave of the same height. That抯 about as big as a normal tsunami gets.

BILL McGUIRE: Well the point about earthquake generated tsunami is that their size is inherently limited by what causes them. Now the biggest submarine earthquakes shift the ocean bed up or down by around 10 metres and that produces tsunami on that sort of scale, but not very much bigger.

NARRATOR: What happened in Lituya Bay seemed inexplicable. It had produced a wave not 10 metres, but 150 metres high. Whatever had caused it, it certainly wasn抰 an earthquake.

GEORGE PLAFKER: We really did not have any idea of just what happened to create the wave evidence that we saw in Lituya Bay. We knew that, you know, Mother Nature doesn抰 give up her secrets readily, but we still were frustrated about the whole thing and we did not expect to ever learn what the answer to our problem was.

NARRATOR: In 1953 the scientists left Lituya Bay baffled, but 5 years later this rare phenomenon was to strike again and this time there were witnesses.

HOWARD ULRICH: The date was July 9th 1958. We came into Lituya Bay about 8 o抍lock in the evening. My son was with me.

SONNY ULRICH: I was 8 years old at the time and being a child like I was halfway asleep as well.

HOWARD: Approximately 10.15 there was a large rumbling noise from up at the head of the bay.

[ Last edited by  naen at 16-11-2008 11:07 PM ]

naen

SONNY: It was like a big loud noise from over in this direction towards the mountains over there.

HOWARD: There was a slight pause. I thought that everything was over with, but some movement up there caught my attention out of the corner of my eye and so I looked directly up there and what I observed was a, like an atomic explosion. After this big flash came a huge wave. It looked like just a big wall of water.

SONNY: He threw me a life preserver and he said son, start praying.

HOWARD: You抮e looking at death and this is exactly my first thought.

SONNY: When the wave hit us I did feel the boat all of a sudden start shooting upwards skywards.

HOWARD: I had 40 fathoms of anchor chain and it started running out off the boat. Came to the end of the 40 fathoms just snapped it like a string and then we were free and, but we were still on the front of the wave. We were swept up over the land and up above the trees. That抯 where I assumed that we were going to end up.

NARRATOR: The Ulriches were lucky. They rode the wave as it swept them above the trees and washed them back into the bay. Two other boats weren抰 as fortunate. They were carried by the wave into the open sea where they were wrecked.

COASTGUARD RADIO: Has there been a first-hand report from any of the boats up there, over? If there抯 any other boats in here, I don抰 think they made it. I don抰 see 慹m and I don抰 hear 慹m. God what an awful sight. You ought to see it in there. Something like the end of the world.

HOWARD ULRICH: I had never heard or seen of anything like this. It was unbelievable. I couldn抰 imagine what could have caused anything. I kept wondering just what mechanism could cause something like that.

NARRATOR: Don Miller flew over Lituya Bay the following day. This is the previously unseen film he took. It shows the utter devastation the wave had created.

GEORGE PLAFKER: Well in 1958 I was out of the country. Don Miller wrote to me and told me about this incredible wave that had occurred in Lituya Bay that stripped the timber and soil off to a height of 520 metres above sea-level. That抯 a half a kilometre high and this is unbelievable, incredible thing, far greater than any wave ever heard of in history.

NARRATOR: This time Miller could see the cause of the wave: a huge section of rock had fallen off a mountain and hit the water at the head of the bay. The impact of this created a wave which washed over the nearby headland and surged towards the open sea. For the first time scientists realised that giant waves could be caused not by earthquakes but by a different destructive force: LANDSLIDES.

GEORGE PLAFKER: Don said why haven抰 we thought of this before? It was a gigantic landslide that fell into the head of the bay, fell from a height of as much as 1100 metres above sea-level and this created a huge splash and wave that then propagated toward the mouth of the bay and creating havoc in its way.

NARRATOR: This is by far the highest wave ever recorded. Normal tsunami are tiny in comparison. The largest tsunami it is possible for earthquakes to generate are around 10 metres high when they are formed. Compared to a skyscraper, that barely reaches the 5th floor, but when it was formed the wave at Lituya Bay reached half a kilometre high, over 50 times the height of an ordinary tsunami. This is higher than any skyscraper on earth.

GEORGE PLAFKER: The mean lesson of Lituya Bay is that a body of rock that抯 large enough and falls from high enough into the water can generate extremely large and violent waves.

GARY McMURTRY: Many people start to think about the sheer size, magnitude of landslide generated tsunamis. They抮e practically unlimited.

NARRATOR: Scientists now began the task of trying to understand this new phenomenon. Tsunami created not by earthquakes but by massive landslides. They called these waves mega-tsunami. Even though landslides happen all the time, we know that mega-tsunami are extremely rare. That is because the vast majority of landslides are too small to generate such a wave. For a mega-tsunami to be created a large amount of rock must be falling fast enough so that when it hits the water it releases a single huge pulse of energy in the form of a wave. Crucially the size of the wave will be directly related to the size of the landslide.

GARY McMURTRY: Landslide generated tsunamis have the potential to be almost unlimited in size. They can basically be as big as the edifice they come from and that means that when something gives way the displacement of the water can also be enormous.

NARRATOR: Scientists in Switzerland have built the most advanced model in the world to study landslide-generated mega-tsunami.

HERMANN FRITZ (Swiss Federal Institute of Technology): What we have here is a very sophisticated laboratory experiment which allows us to physically model landslide impact into water and what we have up here is a very powerful pneumatic landslide generator with the red box where the gravel is filled in to mimic the landslide. The red box is accelerated down the ramp at high speed, the flap opens and the landslide is released to impact the water.

NARRATOR: The scientists here made a detailed analysis of what happened at Lituya Bay where 90 million tons of rock hit the water. They wanted to see how this impact had released enough energy to create a giant wave able to reach half a kilometre high.

HERMANN FRITZ: We adapted our model to mimic a cross-section of Lituya Bay. Up here we have the landslide generator representing the mountain where the rock fell off. At the other end we have a ramp representing the headland where the wave ran up to and what we found when we ran the experiment was fascinating. What we found explains how a wave could reach the extraordinary height of 520 metres. A high speed landslide impacted the water, the water moved away so fast that it couldn抰 flow behind the landslide creating a large air cavity displacing far more water than the landslide volume itself and this explains how a wave can have enough energy to run up half a kilometre and clear out everything in its way.

NARRATOR: The speed and size of the Lituya Bay landslide explains how the wave there could be so big when it was generated. This wave did not travel far. It struck land almost immediately, but mega-tsunami are also able to cross whole oceans. As they radiate outwards their height will drop considerably, yet because they are a powerful single pulse of energy they can travel thousands of kilometres and still cause destruction on distant shorelines.

BILL McGUIRE: The energy that a mega-tsunami unleashes when it hits a coastline is far greater than that of any storm wave imaginable and the reason for this is the huge wave length

naen

(Continued) NARRATOR: travelling fast and pushes against the front making it rise up. This creates the first destructive characteristic of mega-tsunami when they hit the shore. They rear up to become a wall of water. The long wave length also creates a second frightening characteristic. Instead of breaking on the shore the whole length of the wave sweeps onto land engulfing everything before it.

BILL McGUIRE: With storm waves the wave length is just a few tens of metres, but with mega-tsunami it抯 hundreds of kilometres and what this means is that when storm waves break onto a coastline they break almost immediately, but mega-tsunami just keep on coming through the whole length of the wave and this makes them incredibly powerful and incredibly destructive.

NARRATOR: Once scientists understood that landslides into water could produce mega-tsunami they began wondering where the next massive landslide would occur. They looked for where the biggest landslides had happened in the past in the belief it could tell them where they might happen in the future. Geologists knew that one type of location was particularly vulnerable to landslides: LARGE VOLCANIC ISLANDS. There are dozens of such islands scattered throughout the world抯 oceans and the reason they are prone to landslides is because of the way they抮e built. These islands began life millions of years ago when lava erupted onto the ocean floor. As this cooled and hardened layer built upon layer until it formed a land platform of volcanic rubble above sea-level. Scientists realised that every few thousand years one of these piles of volcanic rubble had fallen into the sea.

GARY McMURTRY: Volcanic islands grow by one lava flow after another over tremendous amounts of time. As they do this they become over-steepened. At the same time you have the ocean eroding away at the base and eventually all these things together end up weakening the edifice to the point at where it collapses.

NARRATOR: This is Hawaii, the largest chain of volcanic islands on earth. These scarred valleys are where vast sections of Hawaiian coastline fell into the sea hundreds of thousands of years ago. The mega-tsunami they created would have been thousands of times more powerful than Lituya Bay. Underwater lies the debris of ancient Hawaiian collapses. Whole chunks of the islands have fallen onto the sea floor. The biggest section is the Tuscaloosa sea mount, a giant block which fell off the island of Oahu 2 million years ago. This single rock is almost 10 times the volume of Mount Everest. When it hit the water it would have created an unimaginable mega-tsunami. It would have taken 5 hours to travel across the Pacific and strike the west coast of America, but this event was not unique.

GARY McMURTRY: What we notice when we start looking at the volcanic islands is that every archipelago has collapses. The evidence is insurmountable, everywhere you go you find evidence for debris avalanches, slumps.

NARRATOR: The Cape Verde islands in the Atlantic also had a massive landslide. This was 80,000 years ago. The mega-tsunami this created would have taken just one hour to strike the west coast of Africa. These volcanic island collapses seem to be rare, only happening every several thousand years. The most recent one is thought to have occurred in the Indian Ocean when part of the island of R閡nion collapsed just 4,000 years ago. Seven hours later the wave it generated would have struck Australia. Although this is believed to be the last volcanic island to collapse it seems inevitable that somewhere it will happen again.

GARY McMURTRY: You can抰 build islands over thousands of years flow after flow without having collapse. It just is part of their nature, it抯 part of their history and it抯 part of their future.

NARRATOR: The big question is where and when the next large volcanic island collapse will occur. Because these landslides all happened in the ancient past no-one has ever witnessed one. They are so rare scientists cannot be sure what the precursors will be, but of all the large volcanic islands around the world one in particular shows disturbing signs of instability. If this island collapses it would create a mega-tsunami that would race across the Atlantic and hit the east coast of the United States. Every city on the shoreline would be destroyed. From New York in the north to Miami in the south. The wave would wreak havoc for as much as 20 kilometres inland. The origin of this wave would be thousands of miles away. This mega-tsunami would come from a volcanic island off the coast of North Africa, from one of the Canary Islands. It would come from the island of La Palma. La Palma is one of the western-most islands in the Canaries. 80,000 people live here making their living from farming and tourism. There are also two volcanoes on the island, one extinct, one active. In the early 1990s a British geologist travelled to the island to study the active volcano called the Cumbre Vieja.

SIMON DAY: I came here to work on the Cumbre Vieja volcano with the aim of understanding the history of the volcano and the volcanic hazards that it produced.

NARRATOR: Simon Day was to discover evidence that the next volcanic island collapse is likely to occur here. La Palma consists entirely of two volcanoes. The extinct volcano makes up the northern part, but the southern half of the island is the active volcano, the Cumbre Vieja. This is shaped like a ridge rather than a cone and for thousands of years volcanic vents have regularly erupted all along the summit of this ridge. In 1949 it suddenly erupted again and this eruption was to change everything. Although the eruption itself posed little danger to islanders, shortly after it started an unusual event occurred.

SIMON DAY: About a week after the start of the 1949 eruption something extraordinary happened. There was a series of very strong earthquakes and the west side of the volcano slid downwards and towards the sea by about 4 metres and for about 2 kilometres along the summit of the volcano this fissure opened up. It抯 not an ordinary volcanic vent that just opens horizontally and that magma then erupts out as lava. This side has gone down relative to this side by about 4 metres as this area moved off towards the sea and this was something quite unusual, quite unique that you don抰 normally see on volcanoes.

NARRATOR: A section of La Palma had started to slide and then abruptly stopped. Simon Day couldn抰 be sure what was happening to the volcano and whether it would slide again or even collapse into the sea.

naen

SIMON DAY: The problem was the Cumbre Vieja had erupted many times in its history, but there抎 been no previous history of faulting, so what was so special about the 1949 eruption, why had the faulting occurred then?

NARRATOR: To find out Day had to discover what was happening to the rock structure inside the volcano. This might tell him not just why the fault had appeared, but also whether it was the precursor to a giant collapse. The Cumbre Vieja is still active making it hard to know exactly what抯 happening inside, but the other volcano on La Palma is extinct and its rock structure is the same as the Cumbre Vieja抯. Here there is a place where geologists can look inside a volcano.

SIMON DAY: These tunnels are an amazing opportunity for geologists because they allow us to look into the interior of the volcanoes, going in several kilometres horizontally and up to 2 kilometres below the surface, so what we can see in here uniquely almost in the world is the inside of a volcano.

NARRATOR: Deep underground lay a clue which began to explain not only what had caused the fault above, but also whether one day the Cumbre Vieja would collapse. For what lies in the heart of these volcanoes is surprising: WATER. The volcanoes on islands like La Palma are unusual. They are full of water. Much of the rain which has fallen on La Palma for thousands of years has been trapped inside the volcanoes because of their particular rock structure. Deep within the volcanoes on La Palma are two types of rock. One is permeable rubble which allows rain to soak into it, but standing vertically upright within this rubble is the other type of rock, vast walls of cooled lava which form hardened dykes. These are impermeable and act as dams trapping columns of rainwater in the heart of the volcano.

SIMON DAY: What we抮e looking at here is one of the two types of rock that we find within the heart of volcanoes like the Cumbre Vieja. It抯 very loose, very permeable material, the water can soak straight down through it from the surface, down to this level within the volcano and the second type of rock is this. This is the lava dyke and it抯 very hard, it抯 formed by volcanic lava forcing its way up through the volcano. Once the eruption抯 ended the lava in the dyke solidifies and produces this very hard rock and the important point about this rock is that it抯 very impermeable. The water can抰 penetrate through it, it抯 trapped behind it and these dykes within the middle of each volcano act as a series of dams.

NARRATOR: Simon Day began to wonder if it was the effect of this water on the volcano which could lead to its eventual collapse. He contacted a geologist who studies the forces that build up inside volcanoes, Derek Elsworth. In particular, Elsworth was interested in the effect of water pressure on volcanic collapses.

PROF. DEREK ELSWORTH (Pennsylvania State University): This is a very simple model of how water pressures can cause instability in landslides and we have two inclined bricks. When the bricks are dry with no water pressures acting between the join in these two bricks then just like in a stable volcanic slope there抯 no movement.

NARRATOR: If water is added, however, it begins to force the two bricks apart. The pressure of the water actually lifts the top brick off the bottom.

DEREK ELSWORTH: When we add water between these two bricks if the water pressure抯 high enough to reduce the strength sufficiently, then the upper brick will slide off.

NARRATOR: Although water pressure is enough to push bricks apart, Elsworth realised that water on its own couldn抰 collapse a volcanic island. He discovered that another element needed to be acting on the water: HEAT. For when this type of volcano erupts heat from the magma has a crucial effect.

DEREK ELSWORTH: This represents what happens to ground water in the Cumbre Vieja trapped between the dykes and magma rises within the upper regions of the volcano. This heated bath represents the magma within the volcano. The red water within the flask, like water within the volcano, expands as it抯 heated and as the pressure within the flask increases the only outlet for the water is in this thin tube. This represents what happened within the Cumbre Vieja. As water trapped between the dykes is heated, expands, pressures increase drastically, ultimately causing the flanks of the volcano to collapse.

SIMON DAY: It was tremendously exciting because here was a mechanism that we could use to explain how it was that these enormous masses of rock could be pushed off the side of the islands.

NARRATOR: The heat from an eruption was the final part of the puzzle which explained the forces that would be working in the volcano. When a new column of magma rises and starts erupting water trapped between the dykes will be heated up. This will make it expand, creating enormous pressures within the heart of the Cumbre Vieja. These scientists believe this will trigger the collapse of the western flank of the volcano into the sea.

DEREK ELSWORTH: We found that the relatively small rising temperature in the core of the volcano due to the injection of magma could result in very large changes in water pressures. These water pressures are large enough to produce strength in the flank and result in collapse of the volcano. What this of course means is that the next collapse will ultimately be tied to a future eruption.

NARRATOR: All the conditions for a giant landslide on the Cumbre Vieja are present. It is an active volcano that is full of water. Simon Day needed to find out how big the potential collapse would be and to do that he had to discover the size of the fault within the volcano. He began a detailed survey of all the volcanic vents along the summit to see how extensive the fault was, something no-one had done before.

SIMON DAY: We mapped the volcano from the south to the north and from the south we followed this line of volcanic vents running north up the volcano to here on the summit region. What we found was that the line of vents continued straight off to the north and this told us about how the magma was coming up from deep within the earth up underneath the volcano and erupting at the surface.

NARRATOR: When Day plotted these volcanic vents on a geological map he realised that inside the volcano the fault was far more extensive that it appeared on the surface. It could be as much as 20 kilometres long, dissecting the entire length of the volcano. Potentially one side of the Cumbre Vieja, half a trillion tons of rock, would fall into the sea.

SIMON DAY: When we started analysing the information that we gained by mapping the Cumbre Vieja we found that a change had taken place in the vents of the volcano. The north/south line of vents had extended further to the north with new vents appearing each younger further to the north. This meant that the western side of the volcano was becoming deeply unstable. The whole of this flank was moving towards the sea as a single block.

NARRATOR: The Swiss scientists began to calculate what would then happen. They had to build a new model to estimate the size of the mega-tsunami this event would create. The Cumbre Vieja landslide would be thousands of times larger than any that the scientists had studied before. Because of this, their experiments could only give an approximate figure for the dimensions of the wave.

HERMANN FRITZ: Of course there抯 a huge difference in scale between the Cumbre Vieja collapse

naen

(Continued) HERMANN FRITZ: and its physical model in the laboratory. We抳e tried to err on the side of the caution when we made our calculations using conservative assumptions, but nevertheless what we抳e found when we ran the model was very disturbing.

NARRATOR: The Swiss scientists

naen

MEGA TSUNAMI : WAVE OF DESTRUCTION

Scattered across the world抯 oceans are a handful of rare geological time-bombs. Once unleashed they create an extraordinary phenomenon, a gigantic tidal wave, far bigger than any normal tsunami, able to cross oceans and ravage countries on the other side of the world. Only recently have scientists realised the next episode is likely to begin at the Canary Islands, off North Africa, where a wall of water will one day be created which will race across the entire Atlantic ocean at the speed of a jet airliner to devastate the east coast of the United States. America will have been struck by a mega-tsunami.

Back in 1953 two geologists travelled to a remote bay in Alaska looking for oil. They gradually realised that in the past the bay had been struck by huge waves, and wondered what could have possibly caused them. Five years later, they got their answer. In 1958 there was a landslide, in which a towering cliff collapsed into the bay, creating a wave half a kilometre high, higher than any skyscraper on Earth. The true destructive potential of landslide-generated tsunami, which scientists named "Mega-tsunami", suddenly began to be appreciated. If a modest-sized landslide in Alaska could create a wave of this size, what havoc could a really huge landslide cause?

Scientists now realise that the greatest danger comes from large volcanic islands, which are particularly prone to these massive landslides. Geologists began to look for evidence of past landslides on the sea bed, and what they saw astonished them. The sea floor around Hawaii, for instance, was covered with the remains of millions of years

sekngucing

takut

naen

Originally posted by sekngucing at 19-11-2008 06:26 PM

takut

takut ke?

jangan risau .. kita takkan kena kesan direct daripadanya ..

apepun bencana kat dunia ni, kesan 'semasa' memang aa teruk
(tak kira aa gempa bumi ke, banjir ke, kemarau ke, ribut topan ke)
tapi sebenarnya .. kesan 'selepas' bencana tu yg lagi teruk ..

dapatkah kita (manusia) ni survive? mungkin .. tapi segalanya memang tak pasti

sandra_iskandar

menggerunkan

alphawolf

Satu lagi...kepulauan Hawaii pun tsunami waiting to happen

naen

bakal menghentam hawaii, or berpunca dari hawaii?

kalau tak silap, hari tu ada terbaca yg hawaii tu bakal 'crumble' .. btol ke yek?

tapi kalau ada mega tsunami yg terbentuk dari hawaii,
mungkin tak sampai kot wavenya ke daratan yg lain berhampiran .. mungkin aa ..

naen

nak share ni .. bleh aa klik & tengok

Cumbre Vieja : Atlantic Tsunami Threat

format : flash

selimutpurple

'Due for next tsunami.
BY MICHAEL PERRY
21.12.2009
Reuters.

SYDNEY - A massive undersea earthquake is long overdue beneath the Mentawai islands in Indonesia and would trigger another deadly tsunami,said scientists mapping one of the world's most quake-prone zones.

The announcement comes near the five-year anniversary of the five-year anniversary of the Indian Ocean tsunami, which struck Dec. 26, 26, 2004, and killed about 226,000 people, The possible new tsunami would probably smaller but may be very deadly as it would hit Sumatra's densely populated coast.

"The size of the tsunami may not as big, but the problem is the size of the population is about three times as great," Kerry Sieh, director of the Singapore-based Earth Observatiory, told Reuters.

A major quake measuring around 8.6 magnitude is expected beneath Siberut Island, along the Sunda megathrust, where the Indo-Australian  tectonis plate butts up against the European plate - one of the world's most active fault lines.

When the big quake will strike is not known.

"We say most likely in the next few decades. Thirty seconds to 30 years, somewhere in there," said Sieh, who has studied geological records showing that for 700 years, major quakes have occured along the Sunda megathrust every 200 years.

There have been three major quake cycles: the late 1300s, the 1600s, and between 1797 and 1833.

"The timing between those three sequence is about two centuries," said Sieh, adding a section of the megathrust under Siberut has not ruptured for 200 years, so is due to slip and cause a major quake.'

alphawolf

13# naen

Berpunca dari Hawaii...sebab 'kerapuhan' kepulauan tersebut......

Dan pasal sampai atau tak...wallahualam...tsunami Lituya Bay walaupun megatsunami tak merebak ke laut lepas. Cuma kena ingat, Hilo di Hawaii 2 kali kena tsunami sekali sebab gempa di Alaska 1946 dan Chile 1960...dan tsunami 2004 cukup besar bila sampai di pantai Afrika....