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SAI INTERNATIONAL SCHOOL
STD VII SUBJECT - GEOGRAPHY
TOPIC-CH – 5- WATER(LESSON NOTES)
Sub-topic- WAVES
NOTES- WAVES-The water in the ocean is constantly moving. On the surface we see water
moving in the form of waves. Ocean waves are caused by wind moving across the surface of
the water. The friction between the air molecules and the water molecules causes energy to
be transferred from the wind to the water. This causes waves to form.
The crest is the highest point of the wave.
The trough is the lowest point of the wave.
Tsunamis are large and powerful ocean waves that grow in size as they reach the shore. A
tsunami is a large ocean wave usually caused by an underwater earthquake or a volcanic
explosion. Tsunamis are NOT tidal waves. With typical waves, water flows in circles, but with
a tsunami, water flows straight. This is why tsunamis cause so much damage.
The word Tsunami or ‘harbour-wave’ comes from the Japanese word ‘tsu’, which means
harbour and ‘nami’ which means wave. They are commonly known as ‘killer waves’.
Interesting Facts about Tsunamis
∑ Although tsunamis are sometimes called tidal waves they have nothing to do with the
ocean's tides.
∑ The series of waves generated by a tsunami is called a wave train.
∑ The first wave of a tsunami may not be the biggest. There may be bigger and stronger
waves to come.
∑ The word "tsunami" means "harbor wave" in Japanese.
∑ The warning system in the Pacific Ocean is called the DART system which stands for
Deep-ocean Assessment and Reporting of Tsunamis.
The Asian Tsunami in 2004 in the Indian Ocean is considered the deadliest Tsunami ever,
which was caused by an earthquake with the energy of 23,000 atomic bombs! This brought
with it incredibly destructive waves hitting the coastlines of eleven countries from Thailand to
Africa, killing 283,000 people and wiping out cities.