Tsunami receeding water question

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Discussion Overview

The discussion centers around the phenomenon of water receding from the shore prior to the arrival of a tsunami wave peak. Participants explore the causes of this receding water and compare it to the behavior of regular ocean waves as they approach the shore.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant questions the cause of water receding before a tsunami wave and whether it differs from regular wave behavior.
  • Another participant notes that previous discussions on similar topics exist, indicating ongoing interest and inquiry.
  • A participant expresses the need for a clearer explanation of the physics behind the outflow of water preceding a tsunami, highlighting a lack of consensus in earlier responses.
  • One explanation compares the generation of tsunami waves to the ripples created by dropping a stone in water, suggesting that the initial disturbance leads to a series of waves due to oscillation.
  • Another participant clarifies that the leading wave of a tsunami can be a depression in water level, and discusses the relationship between wave amplitude, ocean depth, and wave velocity.
  • Links to external resources and animations are provided to illustrate the concepts discussed, including the behavior of tsunami waves and their characteristics.

Areas of Agreement / Disagreement

Participants express varying viewpoints on the causes and characteristics of tsunami wave behavior, indicating that multiple competing views remain and the discussion is unresolved.

Contextual Notes

Some participants mention the complexity of tsunami generation and the influence of ocean depth on wave behavior, but these aspects remain inadequately defined and are subject to further exploration.

cbrauner
1. What causes water to leave the shore preceeding the tsunami wave peak?

2. Is the cause of that receeding water different from when regular waves approach the shore?
 
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preceding trough

The two responses regarding the "outflow" of water preceding the tsunami wave do not support each other. I need a better explanation of the physics.

Furthermore, how does a single upthrust of a tectonic plate generate a series of waves?
 
The same way dropping a stone in a lake creates a series of waves - it starts an oscillation that continues until damped. Water is pushed away, then rebounds (actually sending a column of water up), then that water falls away, etc., etc., etc.

http://www.cc.gatech.edu/gvu/animation/Areas/secondary/closeUpDiveSplash.html animation from NOAA, you can see that the biggest trough also preceded the biggest wave (the dark blue line) - obviously its a much more complicated event than a single splash, though. It also looks like what traveled west was a different shape - probably due to the sea-foor shape.

Also, an earthquake isn't a single event: they generally last 30-60 seconds, which also causes a series of waves.
 
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Thank you

Thank you Russ.
We just learned of this website and were figuring out how it works.

This more detailed explanation and links helped to expand and clairfy your first explanation in the other thread. We didn't realize that there were smaller "tsunami" waves that came before the large one or that they could cause such a big trough before the "big" wave first hit land.
 
The 'leading wave' of a tsunami is depression or drop in water level, however the leading wave can also be an elevation or rise in sea level.


A Tsunami is a wave which damps off as its amplitude increases. The increase in amplitude is due to a decrease in waveform velocity due to a shallowing ocean depth and conservation of wave energy.

Tsunami celerity velocity:
[tex]v_c = \sqrt{gd}[/tex]
[tex]g[/tex] - gravitational acceleration constant.
[tex]d[/tex] - ocean depth

A tsunami 'wave recession' is a 'leading wave' of negative amplitude. The negative amplitude height being equal to the height difference between its maximum recession ocean level and its 'normal' ocean level.


Reference:
http://www.prh.noaa.gov/itic/library/pubs/glossary/tsu_glossary_images/bigimage1_pg14.jpg
http://www.scubageek.com/geek/articles/wwwceler.html

Tsunami Photos:
http://img93.exs.cx/img93/6783/tsunami29bh.jpg
http://img93.exs.cx/img93/4707/tsunami39ge.jpg
http://img93.exs.cx/img93/6052/tsunami45sw.jpg
http://img93.exs.cx/img93/4176/tsunami53jm.jpg
http://img84.exs.cx/img84/7036/tsunami61kb.jpg
http://img84.exs.cx/img84/8669/tsunami72fb.jpg
http://www.pmel.noaa.gov/tsunami/Oceans99/Images/pic_1_2.jpg
http://www.buffalonews.com/graphics/2004/12/27/actualsize/1227waves.jpg
 
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