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.
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."
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.
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.
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.
So 692 charts (1647 including sub-charts) are available in the Canada CHS layer. (see coverage)
Note : don't forget to visit 'Notices to Mariners' published monthly and available from the Canadian Coast Guard both online or through a free hardcopy subscription service. This essential publication provides the latest information on changes to the aids to navigation system, as well as updates from CHS regarding CHS charts and publications. See also written Notices to Shipping and Navarea warnings : NOTSHIP
A study has revealed that a growing overdependence on satellite navigation could have catastrophic effects on boaters
Global Positioning System (GPS) gadgets have become such a big part of our lives, both on and off shore, that we are becoming dangerously dependent on the technology, according to a report from the Royal Academy of Engineering.
The GPS uses signals from satellites to provide precise timing and location details to everything from marine chartplotters to mobile phones but those signals are vulnerable to disruption with potentially devastating results.
Since the signals received by GPS systems are very weak – the equivalent to receiving the light from a bright bulb at a distance of 20,000km – they are open to interference or corruption, either from phenomena such as sun spot activity (geomagnetic storm) or malfunctioning TV aerials, to purposeful disruption using jamming broadcasts. Although jammers can be bought legally for as little as £20 online, it is illegal to use them in the UK.
Dr Martyn Thomas, who chaired the group behind the report, said, "We're not saying that the sky is about to fall in; we're not saying there's a calamity around the corner.
"What we're saying is that there is a growing interdependence between systems that people think are backing each other up. And it might well be that if a number of these systems fail simultaneously, it will cause commercial damage or just conceivably loss of life. This is wholly avoidable."
The report investigated the effects of commercially available GPS jamming systems on marine navigation by sailing the Northern Lighthouse Board vessels NLV Pole Star through a patch of sea blanketed by the jamming signal.
This caused the Pole Star's GPS receivers, automatic identification system transponder, dynamic positioning system and gyro calibration mechanism to fail. Each of these systems was in some way controlled by or dependent on GPS.
"What was interesting about the Pole Star, which took place off Flamborough Head, was the range of results that we got," said Richard Ploszek, the Royal Academy of Engineering's senior policy manager responsible for compiling the report. "Some of the readings were quite obviously erroneous, such as placing the ship doing 100 knots above the North York moors, and the GPS software was rejecting those out of hand. But there were others falling into what we would class as the dangerously misleading category, five metres here or there for example. That would be enough to put you on a rock or really play havoc with the precision docking systems of these larger vessels."
The report concluded that: "There were several questions raised by this trial, such as the ability of a vessel's crew to quickly revert to traditional means of navigation and also the extent to which they are able to navigate with these means.
"Given the greater reliance on satellite navigation, in particular GPS, these skills are not being used daily and are no longer second nature."
According to Ploszek, "The problem would be at its worst in a crowded shipping lane with a lot of boats relying on their GPS. Imagine what could happen in the English Channel on a foggy day."
BBCNews : UK 'over-reliant' on GPS signals, engineers warn
Costa Rica this week announced the creation of a vast new marine park several hundred miles offshore. Officials said the move is aimed at protecting the rich diversity of life in this Pacific Ocean region, as well as a group of undersea mountains.
The park, called Seamounts Marine Management Area, covers about 3,900 square miles (10,000 square kilometers) around Cocos Island, an uninhabited speck just over half the size of Manhattan, located 340 miles (550 km) off the coast of this Central American country.
The island is sometimes known as Shark Island for the variety of its finned denizens. White-tipped reef sharks, whale sharks and scalloped hammerhead sharks prowl the island's tropical waters, which also support more than 30 marine species unique to the region.
Costa Rican President Laura Chinchilla Miranda signed the executive decree that established the new park yesterday (March 3), and conservation groups are applauding the move.
"Creating a protected seamount area sets an important precedent," said Marco Quesada, the Costa Rican marine program coordinator for the group Conservation International.
"Seamounts host endemic species, and the deep water that upwells along their sides brings nutrients that support rich feeding grounds for sea life on the surface," Quesada said. "Seamounts serve as stepping stones for long-distance, migratory species, including sharks, turtles, whales and tuna."
A school of sharks lurks just below the ocean surface near Cocos' rocky shore. Photograph by Octavio Aburto
Cocos Island, the center point of the new marine park, is sometimes called Shark Island for the species that congregate around it.
The newly established protected area, which is more than two-thirds the size of Connecticut, expands by five times what was already a no-fishing zone around Cocos Island.
Known as Area Marina de Manejo Montes Submarinos in Spanish, the park is likely to include both fully protected and low-impact fishing zones, and will encourage the sustainable management of the ocean to protect two of the region's threatened species: leatherback turtles and scalloped hammerhead sharks.
Leatherback turtles are listed as critically endangered on the IUCN Red List of Threatened Species. The Costa Rican population of these turtles has declined by 40 percent in the last eight years, and 90 percent in the past 20 years, due in part to the loss of eggs to illegal harvest.
Scalloped hammerhead sharks are on the globally endangered species list, and are often targeted by fishermen for their fins, a prized commodity used in shark fin soup, and a lucrative product on the Chinese market. Both scalloped hammerhead sharks and leatherback turtles are accidentally captured in commercial fishing operations.
National parks and reserves cover more than 25 percent of Costa Rica's land area.
Conservation Int. : Massive new marine protected area offers oasis and hope for endangered sharks and sea turtles
A couple of mobile Marine GeoGarage users report us some problem of geolocalization in our iPhone/iPad universal applications : they don't manage to get a GPS position (so vessel tracking) on the maps.
1/ The first idea is to suspect a trouble of settings :
Just check some setting related to this GPS issue :
in "Settings", accessed via the "General" icon you can find a function labeled, "Location Services"
normally "Location Services" must be "ON" but on the individual App menu, can you check if Marine NZ/US/Brazil is not "OFF"
if it's, turn it "ON" and the GPS problem will normally be resolved.
2/ The second idea is to suspect a trouble with the internal GPS hardware : So check the device is no more in cellular mode but well with the GPS locating method
To investigate the problem, the first step is to download the Free application "GPS Info!" : If the embedded GPS works with GPS Info! or with other mapping applications on the Ipad including the Map App that came with the Ipad as well as other Aps (MotionX...), it must give you :
Lat xx.xxxxxx / Long xxx.xxxxxx / altitude xx meters / locating method GPS
don't hesitate to update the version of your iOS to the current version (4.2 today) and don't hesitate also to update of the Marine NZ/US/Brazil
to help us to solve your problem, you can send us a screen-shoot to have information about your issue. To take an iPhone/iPad screenshot, simply press the sleep button at the top of the iPhone/iPad and the home button at the same time.
The ocean -- it is the most prominent feature on Earth, and of immeasurable importance to life on the planet.
But what would it look like if all of the water was drained out of it? Mountains and valleys that dwarf Everest; shifting plates and undersea volcanoes; seams, ripples, and plains. Though ships have mapped only a small portion of the ocean floor, satellites are used to generate incredibly details maps of the bottom of the ocean. By sensing the minute gravitational changes that pull, push, and bulge the ocean surface, the bottom's shape can be inferred from space.
These bathymetric maps reveal the incredibly dynamic terrain of the ocean. Where available, ship-based measurements are included to provide even higher detail. This visualization tours the ocean floor from the gentle continental slopes to the deepest trenches using data analyzed and archived by NOAA.
Does it look familiar? It is actually the same data that Google has incorporated into Google Earth and Ocean.
Green flash : many think it is just a myth. Others think it is true but its cause isn't known. Adventurers pride themselves on having seen it.
It's a green flash from the Sun. The truth is the green flash does exist and its cause is well understood. Just as the setting Sun disappears completely from view, a last glimmer appears startlingly green. The effect is typically visible only from locations with a low, distant horizon, and lasts just a few seconds. A green flash is also visible for a rising Sun, but takes better timing to spot.
A dramatic green flash, as well as an even more rare blue flash, was caught in the above photograph recently observed during a sunset visible from Teide Observatory at Tenerife, Canary Islands, Spain.
Credit & Copyright: Pekka Parviainen (Polar Image, 1992)
The Sun itself does not turn partly green or blue -- the effect is caused by layers of the Earth's atmosphere acting like a prism.
The green flash is real but it is rarely seen, since it requires special conditions to be observed. The green flash is usually a band or vertical ray of green light just above the setting or rising sun, and can be green, violet, or blue. To see it, you need a clear, flat horizon and a haze free sky. An ocean works well - so do deserts.
The green flash is caused by rays of sunlight refracting (bending) in the atmosphere. Because refraction depends on the wavelength (color) of the light, blue, violet and green light are refracted more than yellow, orange, and red light. So at sunset, when the light has the most atmosphere to be bent by, the sun is surrounded by "shadows" of different colors, with the blue/violet/green shadows farther out. The red, orange, and yellow shadows are abosrbed by the atmosphere, and the blue and violet shadows are scattered by the atmosphere, so the strongest shadow left is usually the green one. This effect is only strong enough to see for a few seconds during sunrise and sunset, hence the "green flash."
To see the green flash again, you'll probably need to watch a lot of sunsets on clear days over the ocean. It really is mostly just a matter of being in the right place at the right time.