PLANET EARTH - The Incredible Visual Guide Part 7 pps

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3 SALT LAKE

Nearly all “fresh water” contains salts of some kind, dissolved from rocks

and soils. As water evaporates from lakes it leaves these salts behind,

and in a hot desert climate this can create a salt lake. The waters of

the Great Salt Lake in Utah are five times as salty as the sea,

and the margins of the lake, seen here, are encrusted with

glittering white salt crystals.

4 SODA LAKE

Typical salt lakes are rich in sodium chloride, or table salt. But some

lakes contain other salts. Many lakes in Africa’s Rift Valley, such as

Lake Nakuru, contain strong solutions of sodium carbonate, or

soda. Despite this, the lake water supports a dense population

of specialized life, including microscopic algae and shrimplike

copepods, which are eaten by vast flocks of flamingos.

5 GLACIAL LAKE

Most of the world’s lakes were formed by ice-age glaciers. The moving

ice scooped hollows in the rock, or dumped thick moraines of rocky

debris in valleys that now act as natural dams, holding back the lake

water. Similar lakes are being formed today by active glaciers like this one

in southern Norway. Meltwater flowing from the glacier in the background

is rich in mineral sediment, which gives the lake its greenish blue color.

6 CRATER LAKE

The craters of extinct or dormant volcanoes often contain

near-circular crater lakes. They fill with pure rainwater, but, if

there is any volcanic activity, the water may become acidified by

gases such as sulfur dioxide and carbon dioxide. The water of this

crater lake in eastern Siberia is unusually acidic, enabling it to

dissolve the minerals that have turned it a milky blue.

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