What is a tsunami?
A tsunami is a wave – or series of waves – caused by a sudden disturbance which vertically displaces a body of water.
While tsunamis are a water-based phenomenon, they are generally started by movements of the Earth - earthquakes,
landslides and volcanic eruptions.
Could an ocean engineer help your community predict or survive a tsunami?
Where do tsunamis happen?
Most signifi cant tsunamis occur near subduction zones – areas
where oceanic tectonic plates meet and slip under continental
plates. These quakes occur when years of stress built up by the
relative movements of two (or more) tectonic plates is released
in a sudden thrust. Due to the size of the tectonic plates, these
earthquakes are among the world’s largest, often exceeding
9.0 on the Richter scale. For the most part, they occur in the
Pacifi c Ocean because it covers and borders one of the most
geologically active regions on Earth.
Do you know what this region is sometimes called?
On December 26, 2004, however, the entire world learned just how powerful and devastating a tsunami in other
oceans could be. A magnitude 9.3 earthquake occurred in the Indian Ocean west of Sumatra and Thailand and east
of India. It generated a series of waves which killed more than 200,000 people in 12 southeast Asian countries.
Satellite images of Banda Aceh, Indonesia, before (L) and after (R) the December 26, 2004, tsunami.
At 9pm on the evening of January 26, 1700 the peace and quiet of the mid-winter was shattered all along the west
coast of North America. From Alaska all the way down to California, people felt the Earth shudder as a huge quake
ripped through the off shore Cascadia fault.
The Huu-Ay-Aht people were at their winter camp at the head of Pachena Bay on Vancouver Island. Today, from
homes built in the same area, they still remember the evening through stories that tell of shaking so long and so
violent it made people sick. What happened after the shaking stopped was worse; the ocean receded and then came
back in a wave so huge that the entire village, except for one person, was swept out to sea. Up and down the coast,
in different nations, Elders repeat the same story with slight variations depending on how hard and how high the
water was when it hit their villages.
Do your Elders tell any stories of tsunamis?
Tsunamis and earthquakes leave signs of their passing on the Earth.
Drowned marsh lands get covered in silt and compacted into the
ground; rocks and animals become misplaced and show up in places
where they do not belong. By studying soil and the ocean fl oor,
scientists can read these signs and the stories they tell. They call
these stories geological evidence.
From the stories told by Elders and the Earth (and records of what
happened when the tsunami made it all the way to Japan) scientists
now believe the killer wave of 1700 was caused by a magnitude 9
earthquake. It occurred when years of stress built up by the relative
movements of the Juan de Fuca and North American tectonic
plates was released in a sudden downward thrust of the underwater
Juan de Fuca.
Geological evidence indicates that 13 massive quakes and tsunamis
have occurred on the west coast of North America in past 6000
years. The most recent one was in 1964. It caused massive damage
along the north west coast from Alaska down to Port Alberni,
BC.
Posted by Aneka Tips
on 16.52. Filed under