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Estuaries, lochs and fjords
If the sea rises, or the land sinks, it can flood the coast. A flooded lowland valley is called an estuary. A flooded valley within mountains is called a fjord,
sea loch or sound.
A
It is easier to work out what
a drowned coast looks like if you
think about a valley that has
recently been used for a reservoir.
Here, the water level has risen
quickly, so the valley sides dip
straight down into the water. There B has been no time for waves to cut
cliffs and there is no beach on
which waves can lap.
Most drowned valleys are the result of how sea levels changed during the ice age (pictures , 2 and 3).
E  These diagrams shows how lochs,
fjords and estuaries are formed during
ice ages. C
(A) What the coast looked like before the Ice Age.
(B) During the Ice Age, the water from the sea is stored as ice on land and the sea level falls. Glaciers and rivers cut deeply into the newly exposed sea bed on their way to the new shore.
(C) At the end of the Ice Age, the ice melts and becomes sea water again. The sea level rises and floods into the deepened valleys, drowning their lower parts. Lochs and estuaries are formed.
Over the centuries, sea levels and land levels change. If the land sinks, or the sea level rises, then many coastlines will be drowned.
Mountain river flows swiftly to the sea.
Lowland river flows gently to the sea.
Glacier
Sea level drops and river cuts into the sea bed.
River
U-shaped valley Cliffs
Loch or fjord
River valley drowned.
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