Download Time (million years) before present S ea Level (cm )

Long-term sea level changes
Sea level rose above or fell below the
present sea level many times due to
• The climatic conditions,
• Plate tectonic processes or volcanic
activity,.
• Melting of glacial ice caps in the polar
regions.
• warming of climate
T ime (million years ) before pres ent
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+150
About 90 million years ago, the sea level
was about 300-400 m higher than today.
Sea level rose by about 120 m during the
last 18000 years, mostly because of the
melting of glacial ice caps in the Polar
Region
S ea Level (cm)
+100
+50
C urrent S ea Level
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The global average rate of rise of sea
level is 1-2 mm/year. This is partly
caused by continued melting of glaciers
and ice caps as a result of warming of
the globe, and partly by the expansion of
near-surface water caused by the rise in
average temperature.
-150
Sea level fluctuations over last 20 million years.
Storms in the Bay of Bengal
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30°N
20°N
10°N
0°
10°S
30°E
50°E
70°E
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30°E
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Cumulative rainfall (colour bar, cm) and storm tracks during June-September and October-January. Data for 19901997 have been used. The light blue (cyan) tracks are for depressions, the red tracks for cyclones (storms), and
the black tracks for severe cyclones. Note the large number of depressions that form in the northern Bay of
Bengal during June-September, when cyclones are fewer. These depressions move northwestward into the
Gangetic plains and bring rain to much of northern India. During October-January, there are fewer depressions, but
the number of cyclones is larger.
• The Bay of Bengal is one of the major centres of
the world for breeding of tropical storms (known
as cyclones over the Indian Ocean, and
southwestern Pacific, as typhoons over the
northwestern Pacific, and as hurricanes over the
Atlantic).
• Cyclones over the Bay of Bengal usually move
westward, northwestward, or northward and cross
the east coast of India or Bangladesh. It brings
strong winds and high rainfall to the coastal
region, causing damage to property and loss of
life.
• Storm surge is primarily piling up of water due to
effect of winds of the storm. It raises the mean
water level in the coastal zone. The magnitude of
rise being dependent on strength of the winds.
For major cyclones rise may be 1-2 meters.
• Rather flat topography of this country makes it
particularly vulnerable to storm surges.