Tsunami is a Japanese word which when translated into English, would mean
“harbour wave‟. Represented by two characters, the top character, „tsu‟ means harbor, while
the bottom character, „nami‟ means wave. In the past, tsunamis were sometimes referred to as
“tidal waves‟ by the general public, and as „seismic sea waves‟ by the scientific community. The
term „tidal wave‟ is however, a misnomer; although a tsunami‟s impact upon a coastline is
dependent upon the tidal level at the time a tsunami strikes, tsunamis are unrelated to the
tides. Tides result from the imbalanced, extraterrestrial, gravitational influences of the moon,
sun, and planets. The term, seismic sea wave is also misleading. Seismic implies an
earthquake-related generation mechanism, but a tsunami can also be caused by a non –
seismic event, such as a landslide or meteorite impact.
2. Tsunamis are unlike wind-generated waves, which many of us may have observed on
a local lake or at a coastal beach, in that they are characterized as shallow-water waves, with
long periods and wavelengths. The wind-generated swell one sees at a California beach, for
example, spawned by a storm out in the Pacific and rhythmically rolling in, one wave after
another, might have a period of about 10 seconds and a wavelength of 150 m. A tsunami, on
the other hand, can have a wavelength in excess of 100 kms in the space of an hour.
3. As a result of their long wavelengths, tsunamis behave as shallow-water waves. A
wave becomes a shallow-water wave when the ratio between the water depth and its
wavelength gets very small. Because the rate at which a wave loses its energy is inversely
related to its wavelength. Tsunamis not only propagate at high speeds, they can also travel
great, transoceanic distances with limited energy losses.4. As a tsunami leaves the deep water of the open ocean and travels into the shallower water
near the coast, it transforms. The tsunami‟s energy flux which is dependent on both its wave
speed and wave height, remains nearly constant. Consequently, as the tsunami‟s speed
diminishes on its way to the shallower water, its height grows. Because of this shoaling effect, a
tsunami, imperceptible at sea, may grow to be several meters or more in height near the coast.
When it finally reaches the coast, a tsunami may appear as a rapidly rising or falling tide, a
series of breaking waves.
5. As a tsunami approaches the shore, it begins to slow and grow in height. Just like
other water waves, tsunamis begin to lose energy as they rush onshore – part of the wave
energy is reflected offshore, while the shoreward – propagating wave energy is dissipated
through bottom friction and turbulence. Despite these losses, tsunamis still reach the coast
with tremendous amounts of energy. Tsunamis have great erosional potential, stripping
beaches of sand that may have taken years to accumulate and undermining trees and other
coastal vegetation. Capable of inundating, or flooding, hundreds of metres inland past the
typical high – water level, the fast-moving water associated with the inundating tsunami can
crush homes and other coastal structures. Tsunamis may reach a maximum vertical height
onshore above sea level, often called a run-up height, of 10, 20, and even 30 metres.
On the basis of your reading of the passage above, make notes using points
Answers
Answer:
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Tsunami is a Japanese word which when translated into English, would mean
“harbour wave‟. Represented by two characters, the top character, „tsu‟ means harbor, while
the bottom character, „nami‟ means wave. In the past, tsunamis were sometimes referred to as
“tidal waves‟ by the general public, and as „seismic sea waves‟ by the scientific community. The
term „tidal wave‟ is however, a misnomer; although a tsunami‟s impact upon a coastline is
dependent upon the tidal level at the time a tsunami strikes, tsunamis are unrelated to the
tides. Tides result from the imbalanced, extraterrestrial, gravitational influences of the moon,
sun, and planets. The term, seismic sea wave is also misleading. Seismic implies an
earthquake-related generation mechanism, but a tsunami can also be caused by a non –
seismic event, such as a landslide or meteorite impact.
2. Tsunamis are unlike wind-generated waves, which many of us may have observed on
a local lake or at a coastal beach, in that they are characterized as shallow-water waves, with
long periods and wavelengths. The wind-generated swell one sees at a California beach, for
example, spawned by a storm out in the Pacific and rhythmically rolling in, one wave after
another, might have a period of about 10 seconds and a wavelength of 150 m. A tsunami, on
the other hand, can have a wavelength in excess of 100 kms in the space of an hour.
3. As a result of their long wavelengths, tsunamis behave as shallow-water waves. A
wave becomes a shallow-water wave when the ratio between the water depth and its
wavelength gets very small. Because the rate at which a wave loses its energy is inversely
related to its wavelength. Tsunamis not only propagate at high speeds, they can also travel
great, transoceanic distances with limited energy losses.4. As a tsunami leaves the deep water of the open ocean and travels into the shallower water
near the coast, it transforms. The tsunami‟s energy flux which is dependent on both its wave
speed and wave height, remains nearly constant. Consequently, as the tsunami‟s speed
diminishes on its way to the shallower water, its height grows. Because of this shoaling effect, a
tsunami, imperceptible at sea, may grow to be several meters or more in height near the coast.
When it finally reaches the coast, a tsunami may appear as a rapidly rising or falling tide, a
series of breaking waves.
5. As a tsunami approaches the shore, it begins to slow and grow in height. Just like
other water waves, tsunamis begin to lose energy as they rush onshore – part of the wave
energy is reflected offshore, while the shoreward – propagating wave energy is dissipated
through bottom friction and turbulence. Despite these losses, tsunamis still reach the coast
with tremendous amounts of energy. Tsunamis have great erosional potential, stripping
beaches of sand that may have taken years to accumulate and undermining trees and other
coastal vegetation. Capable of inundating, or flooding, hundreds of metres inland past the
typical high – water level, the fast-moving water associated with the inundating tsunami can
crush homes and other coastal structures. Tsunamis may reach a maximum vertical height
onshore above sea level, often called a run-up height, of 10, 20, and even 30 metres.
On the basis of your reading of the passage above, make notes using points