309
Lakes
The great lakes are all linked to
each other, and also to the
Atlantic Ocean by the Saint
Lawrence seaway.Volcanic lakes
Rainwater fills the volcanic
crater at the summit of
Mount Mazama, oregon,
to form crater lake. it is
1,932 ft (589 m) deep,
making it the deepest lake
in the United states.WateR fRoM RiVeRs, MoUntain spRings, and rain fills hollows in
the ground and forms lakes, which are areas of water surrounded by land.
lakes also form in depressions dug out of the ground by glaciers, or in
holes in limestone rocks. some lakes are artificial: reservoirs are lakes
made by building dams across rivers. several landlocked seas, such as the
caspian sea and the Dead sea, are really lakes. the caspian sea, which
lies between europe and asia, is the world’s biggest lake. its surface
covers an area almost as large as Japan.
lakes sustain a wealth of plant and animal life and are often
surrounded by fertile land. freshwater lakes provide water for
towns and cities, and recreation areas for swimming, sailing, and
waterskiing. large lakes, such as the great lakes in north america,
are used to transport goods in ships.
However, lakes do not
last forever. silt and
plants can fill up a
lake over a period
of years and turn
it into a swamp.salty lakes
salt collects in lakes that have no outlet,
such as the Dead sea between israel and
Jordan. the water is so salty that people
can float in it without swimming.kinDs of lakes
lakes form in hollows dug by glaciers during the ice age, and in places
where glaciers have left barriers of rock across valleys. Water dissolves huge
holes in limestone regions, which often fill with rainwater to create lakes.
lakes can also form in volcanic craters.fResHWateR lakes
the water in freshwater lakes is not
salty like the sea, because the lakes are
constantly fed and drained by rivers.
the largest group of freshwater lakes are
the great lakes in the United states and canada.
lake superior (left) is the largest of the great lakes.3
Dying lake
the soil
layers extend
into the lake.
plants grow and
the layers
become land.
this continues
until the lake
vanishes.tHe life of a lake
lakes are not permanent features of the landscape.
they may come and go as their water supply
rises and falls. lakes can slowly fill with
soil and stones washed down from the
land above the lake. the outlet river
may deepen and drain the lake.2
sHRinking
lake
the river carries soil,
which falls to the
bottom as it enters the
lake. a layer of soil
builds up along the
edge of the lake.1
yoUng
lake
a river fills a hollow
in the ground to create
the lake. the water
flows through the lake,
running out into
another river.sWaMps anD
MaRsHes
the everglades is a large
region of swamps in florida.
swamps, or marshes, can
form at the edge of a lake
where the ground is soaked
with water or covered with
shallow water. they also
form on land where water
cannot drain away.River
drains lake.Find out more
Plants grow on
the damp,
fertile soil.Soil and mud build up at
sides and bottom of lake.River flows
into lake.Dams
glaciers and ice caps
lake and river wildlife
Marsh and swamp wildlife
Rivers
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