Monitoring

Killer waves come ashore

SOURCE: USGS.GOV, NOAA.GOV, WWW.LIVESCIENCE.COM, NATURAL DISASTERS - PATRICK ABBOTT, WEATHER.GOV, WWW.HOWSTUFFWORKS.COM KEVIN UHRMACHER

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1883 KRAKATOAEruptions of the Krakatoa volcano launched a tsunami. The wave was strong enough to push hundreds of tons of coral onshore. 36,000 killed

1755 LISBON,PORTUGALA large earthquake destroyed Lisbon, Portugal sending people fleeing on boats. A tsunami followed. More than 60,000 killed

1896 JAPANAn earthquake triggered a tsunami that hit the east coast of Japan. Waves are said to have reached 100 feet high. 27,000 killed

1946 ALASKA/HAWAIIAn Alaskan earthquake set off a tsunami that hit Hawaii. 159 killed

1958 LITUYA BAY, ALASKAThe largest tsunami in modern times. An earthquake triggered a landslide, causing a tsunami in the bay that was 1,720 feet high. 2 killed

1960 CHILEAn 8.6 magnitude earthquake in Chile caused a tsunami to reach the Chilean coast within 15 minutes. 1,500 killed

1964 ALASKAThe Good Friday earthquake set off a tsunami more than 200 feet high that traveled more than 400 mph. 120 killed

1976 PHILLIPPINESA tsunami following an earthquake wreaked destruc-tion on the island of Mindanao. 8,000 killed

1998 PAPUA NEW GUINEAA 7.1 magnitude earthquake set off an underwater landslide. 2,200 killed

2004 INDONESIAAn earthquake occurred the day after Christmas. The waves stretched from the Indian Ocean around the world. 230,000 killed

2011 JAPANThe most powerful earthquake to ever hit Japan caused waves as high as 133 feet. A nuclear disaster followed. 16,000 killed

Tsunami risk

Vertical plate movement (earthquake) causes a disturbance in the water. Waves radiate out in all directions from the center of the quake.

At sea, tsunami waves travel fast and have long wavelengths. This makes it difficult to know when tsunami are headed to shore. A network of sensors is set up to detect tsunami formation and send warnings to those onshore who are in danger.

There is no way to know which in the series of waves coming ashore will be the tallest or wreak the most destruction. It can be hours between waves. Destruction is especially bad when it is concentrated in geographically enclosed areas such as inlets or harbors. In that situation, the shape of the land concentrates the force of the wave onshore.

Historic tsunami

3 When waves approach the shore, the sea floor becomes more shallow, forcing waves to grow taller and move more slowly.

Causes of tsunami

Speed

Megatsunami Safety

5-60 mphNormal wavesTsunami

Normal wavesTsunami

Normal wavesTsunami

500-600 mph

Length300-600 ft60-300 miles

Time between waves5-20 seconds10 minutes-2 hours

Meteor impact

Earthquakes

LandslideVolcano

Most tsunami are caused by movements in the Earth’s plates. When plates beneath the ocean shift, water is displaced. Not every earthquake causes a tsunami, though. The amount of vertical displacement of the plates determines if and how large a tsunami forms.

The largest tsunami are caused by a meteoric impact. Speed and size of the impact determine

how devastating the resultant wave will be.

Volcanoes near water are often accompanied by tsunami because the debris flows down the mountain and into the water. Krakatoa is one example of a volcano setting off a tsunami that killed tens of thousands.

Landslides can also cause tsunami when soil barrels into the ocean, kicking up a large wave. Underwater seafloor landslides cause what are called ‘suprise tsunami’ because they begin undetected under the ocean.

AnchorBRP

GOES

Buoy

Regions most at risk of tsunami are near areas of high levels of tectonic activity. Plate boundaries provide the right conditions for vertical displacement of water, causing tsunami to form. The Pacific Ocean, also

known as the ‘Ring of Fire’ is the most active location for tsunami in the world. About 59% of all tsunami take place in the Pacific region.

1. Bottom pressure recorders (BPRs) sense changes in water

pressure.

2. Using an acoustic modem, BPRs signal buoys on the surface of the

water.

3. During normal conditions, buoys relay pressure readings to

GOES satellites.

4. Satellites send the data to onshore warning stations, which

can alert those onshore is a tsunami is imminent.

The Deep-ocean Assessment and Reporting of Tsunamis system is a network of buoys, sensors and satellites tracking

changes in the Pacific Ocean to alert coastal communities to impending tsunami.

If you are on a beach and hear a tsunami warning,get to higher ground immediately. Some natural warning signs that a tsunami is approaching include:

- noticeable rise and fall of beach water- coastal water drains away to reveal coral and/or fish

Even if you think the tsunami is over, don’t return to the beach until you’re given an all clear signal. Tsunami are unpredictable and very dangerous.

The tallest tsunami ever recorded was the Lituya Bay, Alaska megatsu-nami (1958). A rockslide forced waves up to 1,720 ft. high across the concentrated area of the bay.

Megatsunami1,720 ft.

Statue of Liberty 305 ft.

Empire State Building 1,472 ft.

Freedom Tower 1,776 ft.

Red regions indicate area of highest tsunami risk.

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