Tsunami is produced by an undersea earthquake,
an underwater landslide or volcanic eruption.
Tsunami's wave involves deep water [as tides do]
reaching just the ocean bottom.
    In deep water the  l  of  tsunami's wave
may be up to 500 kilometer [300 miles] or greater
and of an height of  50 cm [~ 20 inches].
Tsunami's wave may be as wide as the Pacific ocean.
The speed of tsunami may reach up to 700 Km/h [434 miles/h]
Tsunami is not dangerous in deep water.
Single waves are less than few meters high.
    In shallow water, near the coasts,
the  l of  tsunamis wave
may be of 1.5 - 3 km [1 - 2 miles],
with an height of up to 30 m [100 feet] or  more.

    Tsunami waves loses energy at a rate inversely related to  l.

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The Speed, S, of tsunamis water waves
is obtained from:

                                  S = [g * d] ^0.5

where 'g' equals the acceleration of gravity [ = 9.8 m / s² ]
and d = water depth in meters [m].
Accordingly, the relationship between water depth and the tsunami's waves speed equals: