About Tsunamis Answers

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 Hi all,

Here are the answers to the post About Tsunamis. If you find the link disappears - let me know in feedback! 

Oh, and just so you know, I use Dictionary.com for most of my definitions but remember to take context into consideration!

Part A Vocabulary

To trigger something	To start something			To sweep onto	To move steadily and strongly onto
To shift	To move position			To engulf	To cover completely
A landslide	A downward sliding of a mass of earth and/or rocks			To near	To get closer
To be thrust up	To be pushed up violently			To brake	To stop
The body of water	The huge volume of water in total			Onshore	On the land by the sea
The ripples	Little waves

Part A Questions

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How is an ocean wave caused ?

An ocean wave is caused by the effect of wind on the surface of the sea.

What 3 things can cause a tsunami and what makes it so different from an ordinary wave ?

A volcanic eruption, or a landslide or an underwater earthquake.

A tsunami happens when a huge volume of water, not just on the suface, but right down to the ocean floor, is shifted in one sudden violent motion.

Exactly what happens to the ocean bed when an earthquake cracks the ocean floor ?

One side of the fault is thrust up.

What is the effect of this on the water above it ?

It pushes up the whole body of water above the fracture.

Describe the height and length of a tsunami.

A tsunami has a small wave height and a very long wave length, mid-ocean.

What 3 things happen as it reaches land ?

The water onshore gets sucked back 'drawback) ; the shallow water on the shore acts as a brake, slowing the front of the wave down ; the back of the wave is still travelling fast so it rears up.

How is the wave described ?

A wall of water.

Does it break onshore ? If not, what does it do ?

No it doesn't break onshore, instead, it sweeps onto land, engulfing everything in its path.

Part B Vocabulary

A slab	A broad, flat somewhat thick piece of stone, wood or other solid material				Saw-tooth	Having a zigzag profile similar to the teeth of a saw
Sheer	Perpendicular, very steep				To loom	To come into view in indistinct and enlarged form
A geological fault	A crack in the earth's crust caused by displacement of the two sides				A spring	A coiled wire
Sharp	Having angular lines

Part B Questions

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On what date did the tsunami being described, take place ?

26th December 2004

Why was it of interest to scientists ?

It was such a big tsunami, they wanted to understand how different the earthquake was that had caused it.

What was below the ship ?

A vast undersea chain of mountains.

How have these been formed and over how many years ?

They have been pushed up over millions of years through the action of two tectonic plates.

What did the scientists use to investigate the seabed ?

Remote equipment.

What did they find first ?

A sheer vertical cliff with a sharp, saw-teeth edge that was evidence of the formation of a recent fault.

What did they discover next ?

A second, bigger cliff above the first.

What did this give evidence of ?

A megathrust earthquake.

What is the magnitude of this kind of earthquake ?

Always over 9.

Why did it happen on this particular date ?

After hundreds of years of the plates pushing together, the pressure that had built up reached breaking point on that day.

Hope you did OK! 

 Bye...until the next post!