Why Japan's tsunami triggered enormous whirlpool

Whirlpool created by the earthquake off the coast of Japan, March 11, 2011

From LiveScience

The tsunami that hit northern Japan today created an enormous whirlpool in a harbor off the east coast of that country.
According to researchers, whirlpools aren't unusual after waves of this size.

The tsunami was triggered by an 8.9-magnitude earthquake that struck off the coast of Japan at 2:46 p.m. Tokyo time.
Video footage shows a boat swirling in the massive eddy.
It's not known whether anyone was on the vessel.

Based on eye-witness accounts and video in recent years, whirlpools probably occur with some regularity after large tsunamis, said Ruth Ludwin, a retired seismologist at the University of Washington in Seattle.

"Whirlpools have a big impact on the human imagination," Ludwin said.

ca. 1797-1858 - Whirlpool and Waves at Naruto, Awa Province - by Hiroshige
Image by © Christie's Images/CORBIS

"They're very notable and very frightening. But from the perspective of the geological record, they don't leave any particular sign that has been recognized so far."

Whirlpools happen because of the interaction between rushing water and the geology of the coastline and seafloor, Ludwin said.

"Obviously there is a lot of water that is being pushed around, and it is interacting with the shape, the bathymetry, near the coastline," she said.

"When a tsunami impacts the shoreline, some water overtops the shoreline and advances on the dry land in a manner somehow similar to a dam break wave," Hubert Chanson, a professor of hydraulic engineering and applied fluid mechanics at the University of Queensland in Australia, told LiveScience.
"This was seen during the December 2004 tsunami in Indonesia and Thailand, as well as on Friday, 11 March 2011 in Japan.
At the same time, the impact of the tsunami waters on the coastline induces some very intense turbulent motion, and, with a suitable bathymetry, a large whirlpool may develop."

The first images and videos of post-tsunami whirlpools came out of the 2004 Indian Ocean tsunami, Ludwin said (see abstract).
But eyewitness accounts from previous coastal quakes suggest that tsunami whirlpools are nothing new.
One was reported in the great Lisbon earthquake of 1775, Ludwin said.
The Haida people of the Queen Charlotte Islands off the coast of British Columbia have myths about a whirling wave of foam.

Apela Colorado, Ludwin's colleague with the Worldwide Indigenous Science Network in Hawaii, has identified a petroglyph in southeastern Alaska that seems to show a whirlpool in the body of a sea monster.
In an abstract presented at the 2006 meeting of the Seismological Society of America, Colorado and Ludwin describe the native myths about that monster.
According to ancient tales, they wrote, the creature "inundates canoes, makes the salt-water boil, swallows fishermen, pushes fish into a cave, and creates a canoe passage by flopping across a spit."

Links :

• Hebridean : about the Corryvreckan whirlpool
• Maelstrom in Norway

The fatal shore

Tsunamis : killer waves

From NationalGeographic

A tsunami is a series of ocean waves that sends surges of water, sometimes reaching heights of over 100 feet (30.5 meters), onto land.
These walls of water can cause widespread destruction when they crash ashore.

These awe-inspiring waves are typically caused by large, undersea earthquakes at tectonic plate boundaries.
When the ocean floor at a plate boundary rises or falls suddenly it displaces the water above it and launches the rolling waves that will become a tsunami.

Most tsunamis, about 80 percent, happen within the Pacific Ocean’s “Ring of Fire,” a geologically active area where tectonic shifts make volcanoes and earthquakes common.

Tsunamis may also be caused by underwater landslides or volcanic eruptions.
They may even be launched, as they frequently were in Earth’s ancient past, by the impact of a large meteorite plunging into an ocean.

Tsunamis race across the sea at up to 500 miles (805 kilometers) an hour—about as fast as a jet airplane.
At that pace they can cross the entire expanse of the Pacific Ocean in less than a day.
And their long wavelengths mean they lose very little energy along the way.

In deep ocean, tsunami waves may appear only a foot or so high.
But as they approach shoreline and enter shallower water they slow down and begin to grow in energy and height.
The tops of the waves move faster than their bottoms do, which causes them to rise precipitously.

A tsunami’s trough, the low point beneath the wave’s crest, often reaches shore first.
When it does, it produces a vacuum effect that sucks coastal water seaward and exposes harbor and sea floors.
This retreating of sea water is an important warning sign of a tsunami, because the wave’s crest and its enormous volume of water typically hit shore five minutes or so later.
Recognizing this phenomenon can save lives.

A tsunami is usually composed of a series of waves, called a wave train, so its destructive force may be compounded as successive waves reach shore.
People experiencing a tsunami should remember that the danger may not have passed with the first wave and should await official word that it is safe to return to vulnerable locations.

Some tsunamis do not appear on shore as massive breaking waves but instead resemble a quickly surging tide that inundates coastal areas.

The best defense against any tsunami is early warning that allows people to seek higher ground.
The Pacific Tsunami Warning System, a coalition of 26 nations headquartered in Hawaii, maintains a web of seismic equipment and water level gauges to identify tsunamis at sea.
Similar systems are proposed to protect coastal areas worldwide.

Links :

• DiscoverMag : Waves of destruction
• BOM : Tsunamis facts and information
• NOAA : Tsunamis / Center for Tsunami Research
• NationalGeographic : Learn how the killer waves are formed
  
• BBCNews : Tsunamis, animated guide

Massive 8.9 quake, tsunamis hit Japan

From CNN

An 8.9-magnitude earthquake hit northern Japan on Friday, triggering tsunamis and sending a massive body of water filled with debris that included boats and houses inching toward highways.
The epicenter was 373 kilometers (231 miles) away from the capital, Tokyo, the United States Geological Survey said. But residents there felt the tremors.

The quake rattled buildings and toppled cars off bridges and into waters underneath.
Waves of debris flowed like lava across farmland, pushing boats, houses and trailers toward highways.

In Tokyo, crowds gathered in the streets and tried to reach relatives via cell phone.
Scenes inside office buildings showed papers strewn all over the floor and people clinging onto seats and desks.

Such a large earthquake at such a shallow depth creates a lot of energy, said Shenza Chen of the U.S. Geological Survey.
It caused a power outage in about 4 million homes in Tokyo and surrounding areas.

A tsunami in the Pacific was moving closer to other shorelines in other countries, said CNN meteorologist Ivan Cabrera.
It triggered tsunami warnings for various countries, including Japan and Russia, the National Weather Service said.
"Earthquakes of this size are known to generate tsunamis potentially dangerous to coasts outside the source region," it said.
"Based on all available data a tsunami may have been generated by this earthquake that could be destructive on coastal areas even far from the epicenter."

Video (NOAA)

The quake was the latest in a series in the region this week.
Early Thursday, an earthquake with a preliminary magnitude of 6.3 struck off the coast of Honshu.
A day earlier, a 7.2-magnitude earthquake struck off of Honshu, the country's meteorological agency said.
The largest recorded quake took place in Chile on May 22, 1960, with a magnitude of 9.5, the USGS said.

Links :

• CNN : Tsunami warnings issued for other countries / Hawaii, Russia and Taiwan threatened by tsunami
• Weather.gov : NOAA/NWS Pacific Tsunami Warnings / ETA for locations along the North America Pacific Coast
• NOAA : Tsunami Event - March 11, 2011 Honshu tsunami propagation (YouTube)
• TheGuardian : Japan earthquake - Live updates
• NYTimes : How shifting plates caused the earthquake and tsunami in Japan
• YouTube : Japan Earthquake, helicopter aerial view video of giant tsunami waves /
  
• Google Crisis Response
  

The secret life of a container lost at sea

From NewScientist

Over in California's Monterey bay, an unusual three-day cruise kicked off today.
Marine biologists there are investigating what happens to sea-floor ecosystems when shipping containers are accidentally shed from cargo ships.
With 10,000 containers lost at sea each year, that's a less trivial question than it might seem at first glance.

The project is the result of chance discovery of one such container - plus a legal settlement which resulted in the US government receiving $3.25 million to compensate for the pollution of a national marine sanctuary.

On 25 February 2004, the container ship Med Taipei was caught in 9-metre swells off Monterey bay in central California, heading south for the port of Los Angeles
That night, 15 of its containers broke free of their lashings and toppled into the sea.
Their contents included wheelchairs, cyclone fencing, clothing and recycled cardboard.

That would have been the end of the story, had the remote controlled submersible Ventana, operated by the Monterey Bay Aquarium Reseach Institute (MBARI) in Moss Landing, not happened across the container in June 2004.
Video footage clearly showed the container's serial numbers, which was key to extracting the record-setting payment from the Med Taipei's operators - All Oceans Transportation, Italia Marritema and the Yang Ming Transport Corporation.

This shipping container was discovered upside down on the seafloor by MBARI researchers in June 2004, four months after it was lost at sea.
Researchers will revisit this site during the upcoming cruise.
Image: © 2004 MBARI

Some of the money is now being used to allow scientists from MBARI and the Monterey Bay National Marine Sanctuary (MBNMS) to see what has happened to the ecosystem since the 10-metre-long container landed on the seabed.

The container is lying in 1300 metres of water.
Like most of the deep ocean, the seabed at the site is soft and muddy.
While the 2004 video shows the container looking pristine and uninhabited, it may since have been colonised by species including sea anenomes and deep sea corals, and provided a habitat for fish generally found near rocky reefs.

This map shows the reported position of the container ship Med Taipei when it lost lost 15 containers overboard on February 26, 2004.
It also shows where one of these containers landed on the seafloor, just outside of Monterey Bay.

Introducing an artifical reef might sound like a positive result, but the colonisers could also include predators of the snails, sea cucumbers, brittle stars and other species that live on the muddy bottom - much in the same way as introducing a tree into an upland area can be threaten local rodents by providing a perch for birds of prey.
"You're establishing a new habitat for species to base their foraging from," says James Barry, a senior scientist at MBARI.

While this particular container was carrying a relatively benign cargo of tyres, Andrew DeVogelaere, research co-ordinator for the marine sanctuary, warns that other containers are used to transport toxic materials.
And with some 10,000 containers being lost at sea each year, they may also provide "stepping stones" along shipping routes, facilitating the spread of invasive species that prefer hard-surfaced habitats.

DeVogelaere and his colleagues will explore the container with a newer remotely operated vehicle, the Doc Ricketts.
They will count deep-sea animals on the container and the surrounding seabed, use the submersible's robotic arm to capture those that need to be identified in the lab, and take samples of the sediment for biological and chemical analysis.

Links :

• YouTube : Lost at Sea, the increasing threat from containers and containerships
• ContainerOwnersAssociation : How long do containers float for?
• CEDRE : Containers and packages lost at sea (pdf)