What is Tsunami?
Tsunami is (1) a long high sea wave caused by an
earthquake, submarine landslide, or other disturbance. (2) an arrival or
occurrence of something in overwhelming quantities or amounts. "a tsunami
of data pours into the CNBC newsroom every minute of every trading
day"
A tsunami (pronounced
tsoo-NAH-mee) is a series of waves, made in an ocean or other body of water by
an earthquake, landslide, volcanic eruption, or meteorite impact. Tsunamis can
cause huge destruction when they hit coastlines.
Tsunami (pron: 'soo-nar-me') is a Japanese word; 'tsu'
meaning harbour and 'nami' meaning wave. The phenomenon is usually associated
with earthquakes, landslides or volcanic eruptions in, or adjacent to oceans,
and results in sudden movement of the water column. Until recently tsunami were
called tidal waves, even though the event has nothing to do with tides.
A tsunami is different from a wind generated
surface wave on the ocean. The passage of a tsunami involves the movement of
water from the surface to the seafloor which means its speed is controlled by
water depth. Consequently, as the wave approaches land and reaches increasingly
shallow water it slows. However, the water column still in deeper water is moving
slightly faster and catches up, resulting in the wave bunching up and becoming
much higher. A tsunami is often a series of waves and the first may not
necessarily be the largest.
When a tsunami travels over a long and gradual
slope, it allows time for the tsunami to grow in wave height. This is called
shoaling and typically occurs in shallow water less than 100m. Successive peaks
can be anywhere from five to 90 minutes apart. In the open ocean, even the
largest tsunami are relatively small with wave heights of less than one metre.
The shoaling effect can increase this wave height to a degree such that the
tsunami could potentially reach an onshore height of up to 30 metres above sea
level. However, depending on the nature of the tsunami and the nearshore
surroundings, the tsunami may create only barely noticeable ripples.
Interesting fact: Tsunami can travel at speeds
up to 950km/h in deep water which can be represented by the speed of a
passenger jet.
What causes Tsunami?
Tsunami are waves caused by
sudden movement of the ocean due to earthquakes, landslides on the sea floor,
land slumping into the ocean, large volcanic eruptions or meteorite impact in
the ocean.
Earthquakes - Most tsunami are caused by
large earthquakes on the sea floor when slabs of rock move past each other
suddenly, causing the overlying water to move. The resulting waves move away
from the source of the earthquake event.
Landslides - Underwater landslides can
cause tsunami as can terrestrial land which slumps into the ocean.
Volcanic eruptions - Less common are tsunami
initiated by volcanic eruptions. These occur in several ways:
(a)destructive collapse of
coastal, island and underwater volcanoes which result in massive landslides.
(b)pyroclastic flows, which
are dense mixtures of hot blocks, pumice, ash and gas, plunging down volcanic
slopes into the ocean and pushing water outwards.
(c)a caldera volcano
collapsing after an eruption causing overlying water to drop suddenly.
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