How tsunamis are created – and why these massive waves are so dangerous
Residents of Hawaii are breathing easier but remain cautious after tsunami waves from a powerful undersea earthquake off of Russia’s eastern coast were less severe than originally feared.
Though they start thousands of miles away, tsunamis, the giant waves caused by undersea earthquakes or other disruptions, can cause significant destruction along coastal areas. Tsunamis have caused loss of life with severe floods, erosion, and structural damage.
The 8.8 magnitude quake, one of the strongest in history, erupted July 29 on the Kamchatka Peninsula. Some Hawaiians were ordered to evacuate ahead of tsunami waves, but those orders were later lifted.
Much of Coastal California was under a tsunami advisory and a small section remained under a tsunami warning early on July 30, Paste BN reported.
Here is how tsunamis are created and why they’re so dangerous:
What is a tsunami?
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Tsunamis are a series of giant waves caused by undersea earthquakes at tectonic plate boundaries, or volcanic eruptions. Both displace massive amounts of water, which generate ocean waves that fan out from the quake’s epicenter or the volcano’s vent.
In a process known as shoaling, tsunami waves change dramatically in height and speed as they travel inland. Force from the seabed slows down waves as they reach shallow water. "The shallower the water, the slower the wave," according to sciencelearn.org.
In deep water, newly generated waves can travel at speeds of 500 mph or more, according to the National Oceanic and Atmospheric Administration. “The deeper the water, the faster they move,” NOAA says.
While the waves are moving fast, they’re not very high, usually about 3 feet.
The waves change as they enter shallow water near land, NOAA says:
◾The distance between waves, known as wavelengths, gets shorter.
◾The waves drop in speed to 20 to 30 mph.
◾Height of the waves increases, usually to about 10 feet, though waves as high as 100 feet have been recorded.
Damage caused by tsunamis depends on where they make landfall. Tsunamis can travel significant distances inland, depending on topography and the strength of the waves.
“Reefs, bays, entrances to rivers, undersea features, and the slope of the beach can all influence the size, appearance, and impact of tsunamis when they strike the coast,” NOAA says.
Tsunamis can also be caused by landslides, above or below the ocean surface, or by meteorites.
How did Russian earthquake compare to others?
Why do we call them tsunamis?
Tsunami comes from the Japanese words “tsu” for harbor, and "nami" for wave. Though the term "tidal wave" was once used to describe tsunamis, they are different from tidal waves, which are caused by ocean tides.
Worst tsunamis in history
The deadliest tsunami in history, caused by a 9.1 magnitude earthquake, struck the Indonesian island of Sumatra in the Indian Ocean on Dec. 26, 2004.
About 230,000 people were killed and 1.7 million others were displaced. Economic losses were estimated at about $17 billion.
The costliest tsunami in history took place off the east coast of Japan on March 11, 2011. A 9.1 magnitude earthquake, the largest ever recorded in Japan, caused about 18,000 deaths and about $318 billion in damages.
Shifting tectonic plates
How are tsunamis different from regular waves?
Regular waves are caused by wind. Strong, long-lasting winds create larger waves, with heights varying from 3 to 11 feet. Compared to tsunamis, they move relatively slowly, and their wavelengths are short, measured in feet. They reach the shore every few seconds.
Tsunamis are created by undersea disruptions and travel much faster than regular waves. Their wavelengths can be measured in miles, and they reach the shore minutes or hours apart. Their wave heights can range from 10 feet or more, reaching 100 feet in extreme cases.
Can you surf in a tsunami?
The short answer is no. Tsunami waves are different than regular waves used by surfers, says the University of Hawaii:
◾Tsunami waves do not have faces – the concave sections of waves – so there’s nothing for a surfboard to grip.
◾Tsunami waves are filled with dredged-up trash.
◾A tsunami wave approaching land is more like a wall of whitewater.
CONTRIBUTING Dinah Voyles Pulver, Thao Nguyen, Will Carless, Kathleen Wong, John Bacon, Joel Shannon, Jeanine Santucci
SOURCE Paste BN Network reporting and research; Reuters; National Oceanic and Atmospheric Administration; sciencelearn.org; National Geographic
(This story was updated to include video.)