English subtitles for clip: File:So funktionieren Geysire (CC BY 4.0).webm

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Geysers are a marvel of nature.

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Iceland is famous for its hot springs,
ice-cold glaciers and volcanoes.

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Around 30 volcanoes on the island
are considered active.

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But why do many hot springs
just boil about?

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And others leave the water
more or less explosively

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with a steaming fountain?

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For the rare phenomenon of a geyser

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several factors
must work together perfectly.

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Hot water is an indispensable
part of a geyser.

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There is a "hot spot" under Iceland.

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Like a Bunsen burner,

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rising hot material keeps
melting the earth's crust.

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Magma rises through these "plumes".

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The liquid rock from inside the earth
is the basis for the many volcanoes.

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And the unique thermal system,

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that the human takes advantage
of everywhere on the island.

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For a thermal spring to become a geyser,

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volcanic energy is not enough.

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A geological peculiarity
is still required.

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Geysers always come from a narrow shaft.

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The volcano heats the water from below.

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But the weight of the water column
in the shaft exerts so much pressure

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that the water doesn't start boiling
and evaporating at 100 °C as usual.

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The water remains fluid
at higher temperatures.

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We know the principle
from the pressure cooker.

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When the water gets so hot,

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that from bottom to top gas bubbles form,

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the steam pushes some water
out of the shaft.

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The pressure changes due to the relief.

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Now the water is boiling explosively,

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the volume multiplies up to 1600 times.

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This also explains the high energy

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with which the geyser the mixture
of steam and water hurls upwards.

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Geysers are rare and also very sensitive.

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The smallest changes can dry them up.