How Tsunamis Work
A major earthquake that struck Chile overnight has sent a tsunami out into the Pacific Ocean, prompting a tsunami watch along the coasts of California and parts of Alaska and a tsunami warning for Hawaii.
A watch is a cautionary statement that does not mean waves are imminent. Officials are not sure what nations could be affected bytsunami, but they caution that the entire Pacific Basin is at risk.
A warning, as issued for Hawaii, means waves are imminent and residents should seek high ground. Early reports of waves exceeding 7 feet have been reported near the epicenter of the earthquake. The 8.8-magnitude temblor was centered offshore, 200 miles (325 km) southwest of Santiago, Chile.
"A tsunami has been generated that could cause damage along coastlines of all islands in the state of Hawaii," according to a bulletin from NOAA, the parent organization of the National Weather Service. The waves would be expected to reach Hawaii starting at 11:19 a.m. local time.
Other than timing, however, tsunamis are highly unpredictable.
How tsunamis work
A tsunami is not a single wave, but a series that behave much like the waves rippling out from a stone dropped in a pond. Each wave can last five to 15 minutes, and the danger can last for hours after the initial wave arrives.
"Tsunami waves heights cannot be predicted and the first wave may not be the largest," according to today's NOAA statement.
Tsunamis, which can travel over the ocean surface from many hundreds of miles, can be generated when chunks of the planet's crust separate under the seafloor, causing an earthquake. Here's what happens: One slab of lifting crust essentially rapidly acts as a giant paddle, transferring its energy to the water.
Tsunamis can also be caused by volcanic eruptions, underwater detonations and even landslides.
The resulting waves are hard to predict for several reasons. Nobody knows how a quake has affected the seafloor until hours, days or even months after the event. And a tsunami is almost imperceptible on the open ocean, rising to full ferocity only as it nears the shore.
While more tsunami-sensing buoys cover the ocean than before the devastating 2004 Indian Ocean tsunami, these waves can still be missed.
Not all seafloor earthquakes will generate a tsunami — if the friction between the crustal plates occurs very deep below the ocean floor or move in a way that causes a minimal paddle effect, a tsunami isn't as likely to form.
Major tsunamis in history
The 2004 quake just off the coast of Sumatra, Indonesia, was colossal, eventually put at magnitude 9.3. But an 8.7-magnitude earthquake in 2005 that originated at the same location, while large enough to generate a devastating tsunami, scientists say, did not do so. The exact reasons remain mysterious.
The 2004 tsunami, and those spurred by the 9.2-magnitude Great Alaska Earthquake in 1964, were examples of teletsunamis, which can cross entire oceans.
Several devastating tsunamis have occurred throughout recorded history, including one that leveled Lisbon, Portugal in 1755 and one generated by the explosion of Krakatoa in Indonesia that drowned an estimated 36,000 people.
Except for the largest tsunamis, such as the 2004 Indian Ocean event, most tsunamis do not result in giant breaking waves; instead they come in much like very strong and fast-moving tides, according to the U.S. Geological Survey. As a tsunami nears the shoreline, the rising seafloor forces a wave that might have been just inches tall into a monster that can be several feet high.
The Pacific Ocean basin is particularly prone to tsunamis. Last year, a study of earthquake faults off the coast of Alaska predicted that the risk of tsunamis for the U.S. West Coast is higher than had been thought. Previous research found that a major tsunami hitting Southern California could cause $42 billion in damage.
Tsunamis in History
Some of the biggest, most destructive and deadliest tsunamis on record:
8,000 years ago: A volcano caused an avalanche in Sicily 8,000 years ago that crashed into the sea at 200 mph, triggering a devastating tsunami that spread across the entire Mediterranean Sea. There are no historical records of the event – only geological records – but scientists say the tsunami was taller than 10-story building.
Nov. 1, 1755: After a colossal earthquake destroyed Lisbon, Portugal and rocked much of Europe, people took refuge by boat. A tsunami ensued, as did great fires. Altogether, the event killed more than 60,000 people.
Aug. 27, 1883: Eruptions from the Krakatoa volcano fueled a tsunami that drowned 36,000 people in the Indonesian Islands of western Java and southern Sumatra. The strength of the waves pushed coral blocks as large as 600 tons onto the shore.
June 15, 1896: Waves as high as 100 feet (30 meters), spawned by an earthquake, swept the east coast of Japan. Some 27,000 people died.
April 1, 1946: The April Fools tsunami, triggered by an earthquake in Alaska, killed 159 people, mostly in Hawaii.
July 9, 1958: Regarded as the largest recorded in modern times, the tsunami in Lituya Bay, Alaska was caused by a landslide triggered by an 8.3 magnitude earthquake. Waves reached a height of 1,720 feet (576 meters) in the bay, but because the area is relatively isolated and in a unique geologic setting the tsunami did not cause much damage elsewhere. It sank a single boat, killing two fishermen.
May 22, 1960: The largest recorded earthquake, magnitude 8.6 in Chile, created a tsunami that hit the Chilean coast within 15 minutes. The surge, up to 75 feet (25 meters) high, killed an estimated 1,500 people in Chile and Hawaii.
March 27, 1964: The Alaskan Good Friday earthquake, magnitude between 8.4, spawned a 201-foot (67-meter) tsunami in the Valdez Inlet. It traveled at over 400 mph, killing more than 120 people. Ten of the deaths occurred in Crescent City, in northern California, which saw waves as high as 20 feet (6.3 meters).
Aug. 23, 1976: A tsunami in the southwest Philippines killed 8,000 on the heels of an earthquake.
July 17, 1998: A magnitude 7.1 earthquake generated a tsunami in Papua New Guinea that quickly killed 2,200.
Dec. 26, 2004: A colossal earthquake with a magnitude between 9.1 and 9.3 shook Indonesia and killed an estimated 230,000 people, most due to the tsunami and the lack of aid afterward, coupled with deviating and unsanitary conditions. The quake was named the Sumatra-Andaman earthquake, and the tsunami has become known as the 2004 Indian Ocean tsunami. Those waves traveled the globe – as far as Nova Scotia and Peru.
Tsunami Waves Channeled Around the Globe in 2004 Disaster
Global map showing the spread of waves from the 2004
Sumatra tsunami. Waves followed mid-ocean ridges all over the globe.
Sumatra tsunami. Waves followed mid-ocean ridges all over the globe.
Waves from the Dec. 2004 tsunami traveled as far as Nova Scotia and Peru. Now scientists say that the waves followed mid-ocean ridges like train tracks to get there.
Using satellite imagery and computer simulations, scientists have shown that the Southwest Indian Ocean Ridge and the Mid-Atlantic Ridge – long mountain ranges on the seafloor – steered waves through the Atlantic Ocean.
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Real Tsunami May Have Inspired Legend of Atlantis
Like sound or light waves, tsunamis have a wavelength
, crests and troughs that could be cancelled out to
effectively cloak, say, an oil rig and protect it from the waves,
based on new technology. But practically pulling such
complex cloaking off will require a lot more research.
, crests and troughs that could be cancelled out to
effectively cloak, say, an oil rig and protect it from the waves,
based on new technology. But practically pulling such
complex cloaking off will require a lot more research.
The volcanic explosion that obliterated much of the island
that might have inspired the legend of Atlantis apparently
triggered a tsunami that traveled hundreds of miles to reach
as far as present-day Israel, scientists now suggest.
that might have inspired the legend of Atlantis apparently
triggered a tsunami that traveled hundreds of miles to reach
as far as present-day Israel, scientists now suggest.
The new findings about this past tsunami could shed light
on the destructive potential of future disasters, researchers
added.
on the destructive potential of future disasters, researchers
added.
The islands that make up the small circular archipelago of Santorini, roughly 120 miles (200 km) southeast of Greece, are what remain of what once was a single island, before one of the largest volcanic eruptions in human antiquity shattered it in the Bronze Age some timebetween 1630 B.C. to 1550 B.C.
Speculation has abounded as to whether the Santorini eruption inspired the legend of Atlantis, which Plato said drowned in the ocean. Although the isle is often regarded as just an invention, the explosion might have given rise to the story of a lost empire by helping to wipe out the real-life Minoan civilization that once dominated the Mediterranean, from which the myth of the bull-headed 'minotaur' comes.
The primary means by which the eruption potentially wreaked havoc on the Minoan civilization is by the giant tsunami it would have triggered. However, the precise effects of this eruption and killer wave have been a mystery for decades.
Now scientists find the tsunami may have been powerful enough to race some 600 miles (1,000 km) from Santorini to reach the farthest eastern shores of the Mediterranean, leaving behind a layer of debris more than a foot thick by the coast of Israel.
Researchers dove as far as 65 feet deep (20 meters) off the coast of Caesarea in Israel to collect tubes of sediment, or cores, more than 6 feet long (2 meters) from the seabed.
"The work resembles a construction site with pneumatic hammers, heavy weights, floats to counter-weight equipment, hoses — Each time we took the system down it took hours of surface preparation, planning, and discussion," said researcher Beverly Goodman, a marine geoarchaeologist at Interuniversity Institute for Marine Sciences at Eilat, Israel.
Within the cores, they found evidence of up to nearly 16 inches of sediment deposited roughly about the date of the Santorini eruption. The range of sizes of the particles making up this deposit is the kind one might find laid down by a tsunami — storms, in comparison, cannot kick up the seafloor as much, and as such the range of particle sizes they generate is more limited.
The discovery was very much an accident, Goodman noted. They were actually researching the demise of the harbor of ancient Caesarea, the cause of which remains hotly debated, with culprits including earthquakes and tsunamis.
"I was testing how two later Roman and Byzantine tsunami deposits could be characterized by studying the different grain sizes — various sand, pebbles, rocks, ceramic pieces — in the deposit. Based on determining this 'signature,' I then noticed that there were more than the expected number of tsunami deposits," she explained. "I had no expectation that remnants of the Santorini event would be present in the cores."
These findings support the idea that the Santorini eruption and the side effects from it, such as the tsunami, were massive.
"In the case of the eastern Mediterranean, there seems to be a surprising dearth of archaeological sites along the coastline following the Santorini eruption event," Goodman said. Either archaeologists have failed to concentrate on this time span, "which isn't the case," she said, or the tsunami had a very real impact on coastal settlements.
The dramatic changes in life triggered by the tsunami "might have been part of the fabric of the Atlantis story," Goodman added. "The network of sea-based trade was rather sophisticated in that period, and colonies that were nearly solely dependent on those trade routes existed. It is hard to imagine that such a far-reaching disaster didn't cause them severe shortages in supplies, wealth and power."
Although Atlantis itself "is a myth and legend, it is informative about the experiences of the ancients," Goodman said. "It may very well be the case that those passing the story on had heard of or witnessed events in which coastal buildings went underwater because of earthquakes; beachfront towns were flooded during tsunamis; islands were created by underwater volcanic activity. There may be that grain of truth that lent legitimacy and a certain reality to the legend of Atlantis."
To better reconstruct the Santorini tsunami, the scientists plan to analyze deposits closer to the eruption, such as on Crete and in western parts of Turkey. Knowing the potential effect of tsunamis could be critical for the coastal planning and management, Goodman said, adding that the eastern Mediterranean is very highly populated and possesses considerable sensitive infrastructure such as power stations.
"I suppose there is always the question of whether I think another tsunami will occur in the eastern Med," Goodman said. "The answer is yes. I actually checked the elevation of the house I am moving to near Caesarea before agreeing to move there."
Goodman and her colleagues detailed their findings in the October issue of the journal Geology.
