Geysers
by Elaine Langlois
The people on the great boardwalk in Yellowstone National Park are excited.
Before them, a gently sloping mountain of earth has begun to push out water.
Suddenly, a huge column of water
and steam rushes up 180 feet
high. That’s higher than the
Statue of Liberty, from torch to
base. The water is nearly at
boiling point, and the steam is
hotter than 350 degrees!
Old Faithful has put on another
spectacular show.
Old Faithful is a geyser, a hot
NPS Photo
Old Faithful: Upper Geyser Basin
spring that erupts from time to
time, shooting water and steam into the air. A geyser is like a volcano, except its
eruptions do not produce lava, but water. You find geysers in places where there
is or once was volcanic activity.
For a geyser to exist, conditions must be just right. A geyser needs three things:
1. Water
2. Heat
3. Special plumbing
Water
A geyser needs a good, steady supply of water. Old Faithful shoots out from 3,700
to 8,400 gallons of water in one eruption—and it erupts about 20 times
every day!
A geyser gets its water from snow and rain. Most of the water from snow and
rainfall runs off into oceans, rivers, and streams. But some works its way down
through the earth’s surface to become groundwater. It can take hundreds of
years for water to travel down through rock and come back up in an eruption.
The water erupting from geysers today fell from the sky in the time of
Christopher Columbus!
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Heat
Where does a geyser get its heat? From magma. Magma is hot liquid rock from
deep inside the earth. Magma is so hot that it can melt steel! In volcanic places,
pools of magma reside beneath the earth’s surface. When magma breaks through
the surface, we call it lava.
Plumbing
A geyser needs a special plumbing system. That is what makes the difference
between a hot spring, where heated water rises gently to the earth’s surface,
and a geyser. A geyser’s plumbing
system consists of one or more cracks
or crevices in rock that take the form of
tubes or pipes. It may also include
caverns or chambers where
water collects.
The rock that encloses a geyser’s
plumbing system contains large
amounts of silica. Water flowing
through the cracks pulls silica out of
the rock. Over time, the walls of the
crevices are lined with silica. The silica
gives the “pipes” a watertight seal.
Finally, the plumbing system of a
geyser has one or more places where
the “pipe” is very narrow or bends.
These are called constrictions.
How a Geyser Works
1. Water from rain and snow makes its way down through the earth. It comes in
contact with magma or solid rock that has been heated by magma.
2. The hot, solid rock or magma heats the water until it boils.
3. The hot water and steam begin to rise and fill the geyser’s plumbing system.
In the meantime, cool water is still coming down from the earth’s surface.
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4. At last, the geyser’s plumbing system is full, or close to it. Steam keeps heating
the water until it is hot enough to boil, and hotter. But the weight of the cooler
water above, the watertight “plumbing,” and the constriction act like a stopper
to hold down the hot water and steam.
5. At last, the water starts to boil. Steam forces some of the water up and out.
The weight of the water lessens, allowing water deep inside the geyser to boil.
It flashes into steam, quickly expanding to more than 1,500 times its original
size. The steam and boiling water roar up out of the geyser’s pipes, driving the
water above them.
The eruption continues until the geyser runs out of water or the temperature
drops below boiling. Then the whole cycle starts again.
Kinds of Geysers
A geyser in Iceland called Geysir was the first widely known geyser. As you might
guess, geysir, which means gusher in Icelandic, gave geysers their name.
Major Geyser Fields
There are two types of geysers. Cone geysers, like Old Faithful, erupt in a
steady jet of water and steam. They may have a cone, like the cone of a volcano.
The cone is formed from silica deposited by the geyser water around the crack
where geyser erupts.
Fountain geysers erupt in a series of bursts, usually from beneath a pool of
water. Water and steam spray around, like a fountain.
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Each geyser is different! Some erupt for just a few minutes. Others never stop. A
few, like Old Faithful, erupt regularly. For others, you can’t tell when an eruption
will happen. Like volcanoes, geysers can lie dormant for years and then start
up again.
Earthquakes can trigger changes in geyser activity. In 2002, a powerful
earthquake in Alaska caused more than 1,000 small quakes in Yellowstone,
nearly 2,000 miles away. Some geysers began to erupt more often. Others
erupted less. Some hot springs turned into geysers.
Endangered Geysers
Geysers may live as long as a few thousand years: not long, compared to other
geologic features. The special conditions they need to exist can easily disappear.
Some geysers lose their source of heat or water. Others blow themselves up with a
forceful eruption. Volcanic activity, landslides, and other natural processes can
destroy geysers, too.
The other threats to geysers all come from people. The fierce volcanic heat and
huge water supplies that fuel geysers are ideal for making electricity. Tourists
throw things like trash and rocks into geysers, blocking them up. People take
geysers apart, looking for gold and other valuable minerals. There are only about
a thousand geysers in the world. Because of people, they are becoming even
more rare.
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