Geyser in Yellowstone National Park is thought to be
the oldest geyser in the world. (Copyright
Lee Krystek, 2000)
Geysers are some of the most unusual geologic
phenomena in the world. They are incredible natural fountains
that can shoot boiling hot water and steam hundreds of feet
into the sky in violent eruptions. While most geyser eruptions
last only a few minutes, some last for days. Some geysers almost
never stop. Others erupt violently, then stay dormant for years
or even decades.
While geysers are rare (there are less than 700
known geysers in the world) they are not impossible for the
average person to observe. They exist on every continent in
the world, except Antarctica. The premiere place to see geysers,
however, is Yellowstone National Park in the United States.
Yellowstone is home to more than half of all the geysers on
Technically the U.S. Geological Survey defines
a geyser as: A hot spring characterized by intermittent discharge
of water ejected turbulently and accomplished by a vapor phase.
What makes a geyser act the way it does? In order for a geyser
to exist, there are four specific conditions that must be met.
First, there must be an abundant supply of
surface water over a long period of time. It is estimated
that Yellowstone's geysers discharge a staggering seventy-million
gallons of water a day. The water a geyser ejects comes from
snow and rain. When precipitation hits the ground, most of it
runs off into rivers and streams. A small portion, perhaps five
percent, soaks into the ground. Moving slowly through tiny cracks
it finds its way into the underground tunnels that make up the
plumbing of a geyser, then is shot to the surface during an
eruption. Travel from the surface down through the rock and
out through a geyser eruption can take 500 years. Water we see
today shooting out of geysers fell from the sky in the time
there must be a volcanic heat source. All geyser field
sites are above recently active volcanic areas. The surface
water works its way down to a depth of around 7,000 feet where
it meets up with hot rocks. The water is heated up to 500 degrees
Fahrenheit or more, but cannot turn into steam because of the
pressure it is under.
Though the water is hot and under pressure it
would never be ejected from geysers with such tremendous force
if it were not for the special quality of the rocks in the geyser
fields. The rocks produce a material called geyserite.
Geyserite, which is the third necessary condition, is mostly
silicon dioxide, is dissolved from the rocks and deposited on
the walls of the geyser's plumbing system and on the surface
around the geyser. The deposits make the channels carrying the
water up to the surface pressure-tight. This allows the pressure
to be carried all the way to the top and not be leaked out into
the loose gravel, soil or sand that are normally under the geyser
The final condition needed to produce a geyser
is a plumbing system below it with a special shape. All springs
must have a set of channels below them that allow water to flow
to the surface. In a geyser there must be a constriction at
some point near the top. The water sitting in this narrow spot
acts as a valve or lid that allows pressure to build up in the
water below. When enough pressure builds up to overcome the
constriction, the geyser erupts.
The need for the right combination of conditions:
abundant water, volcanic heat, geyserite and a special underground
shape, are why geysers are so rare. If there is heat, but not
enough water a fumarole appears.
A fumarole is a steam vent. There is so little water in this
type of hot spring that while coming to the surface it boils
away, and all that you see is a hole in the ground with steam
coming out of it, often accompanied by a roaring or rushing
sound. Fumaroles often have the smell of "rotten eggs"
because small amounts of hydrogen sulfide get mixed in with
A fumarole that comes up in a wet surface area
can become a mud pot. As the steam bubbles up through the water,
the hydrogen coming up with the steam reacts with the water
to form sulfuric acid. This melts the surrounding rock to turn
the water into a muddy clay. Mud pots bubble and can throw lumps
of clay for some distance when they are active.
a constriction near the surface a hot spring will not
develop into a geyser, but a quiet pool. (Copyright
Lee Krystek, 2000)
If heat, geyserite and water are present, but
not the right shape, you can get a simple hot spring. Without
the constriction at the top of the spring's plumbing system,
the boiling water simply flows up to the surface and gently
into a pool. Very hot springs are extremely clear as the water
is pure and too hot to support the growth of algae or most bacteria
as a normal stagnant pond would. While the water is pure, it
is not recommended for drinking as small amounts of dissolved
minerals, such as arsenic and sulfur, may be present. Most pools
have a deep blue color caused by the absorption of all other
colors of the light spectrum by the water. Pools can sometimes
turn into geysers and visa versa when conditions change. Sometimes
a hot spring only known to be a pool will surprise watchers
when it erupts and turns into a geyser without warning, though
such events are rare.
Probably the most famous geyser in the world is
Old Faithful at Yellowstone National Park. It was named by members
of the Washburn Expedition of 1870 because it is the most frequently
erupting and predictable of the big geysers. Old Faithful sends
up 8,400 gallons as high as 184 feet on an average of every
85 minutes. It's a "cone" type geyser, which means
that the geyserite deposited over the centuries by Old Faithful
has created a cone shape. By measuring geyserite deposits on
the cone and carbon-dating pieces of wood caught in the geyserite,
scientists have estimated that Old Faithful is roughly 300 years
old. Experts figure that geyserite formations grow at a rate
of less than one inch per 100 years. Before Old Faithful existed
as a geyser it was a regular hot spring for several hundred
years. Further examination of the area around it indicates there
may have been previous geysers and hot springs on the site.
The oldest geyser in the world is thought to be
Castle Geyser, which is located only short walk from Old Faithful.
The size of its cone, in the shape that reminds people of a
castle, indicates that it may be somewhere between 5,000 and
40,000 years old. Despite its age, Castle still gives spectators
a good show by erupting every 10 to 12 hours for almost as long
as an hour.
In addition to the "cone" style of geyser,
there is a "fountain" type of geyser. In a "cone"
geyser, the geyserite has formed a type of nozzle near the surface.
This tends to make the "cone" geysers erupt by sending
a column of water to a great height. In a fountain-type geyser
there is an open crater that fills with water before or during
the eruption. These geysers produce an eruption where the water
and steam come in bursts and water is sprayed around in all
directions instead of creating a single column.
Old Faithful of Yellowstone (a cone-type geyser) erupt
in this video - AVI 396KB
then compare it with the action of Echinus (a fountain
type geyser). - AVI 245KB
In both types of geysers the same mechanism causes
the eruption. Water flowing into the geyser's plumbing system
is superheated by the hot volcanic rock deep below the surface.
It reaches a boiling point and wants to turn to steam, but it
can't. When water turns to steam it greatly increases in volume
(This is the same principle by which steam engines work). The
pressure of the water in the plumbing system above keeps the
water from expanding. Eventually the pressure builds to a point
where the water in the top can no longer keep the superheated
water below from turning to steam. As it does, it pushes the
water out of the top of the geysers starting the eruption. Since
there is less water above after that, there is less pressure
below allowing more of the superheated water to turn to steam.
This pushes the eruption further along.
The eruption continues until all the water is
pushed out. The expulsion of the water may be followed by a
period where only steam escapes from the geyser. Steamboat geyser,
the largest geyser in the world, that can throw water 300 feet
into the air, follows its water phase with phase where steam
roars out of it for hours.
Geologically speaking, no geyser exists for very
long. The dynamics of the geothermal systems that drive them
are always changing. An example of this is Porkchop Geyser at
the Norris geyser basin in Yellowstone. Originally it was a
small hot spring that occasionally erupted. Slowly it sealed
itself closed with geyserite so that pressure build up and in
1985 it started erupting continuously. Pressure continued to
built up so much that in 1989 it exploded. The explosion turned
the geyser back into a small hot spring that is now it working
on sealing itself up again.
Faithful is one of the largest and most predictable
geysers at Yellowstone National Park. (Copyright
Lee Krystek, 2000)
Earthquakes often change the function of a geyser.
In 1959 when an earthquake hit Hebgen Lake, Montana, near Yellowstone,
many geysers went off simultaneously, often with heights and
durations never seen before. While most of the geysers resumed
their normal activity in a few weeks, some were changed forever.
Man's activity can also have an effect on geysers.
Vandalism of a geyser can kill it. Minute geyser in Yellowstone
was close to a 19th century stagecoach stop and travelers waiting
for coaches would toss coins into the geyser. This eventually
plugged up the geyser's plumbing and now its eruptions
rise barely a foot high. Another geyser in California's Napa
valley was foolishly capped to provide hot water heat for a
More recently, attempts to tap geothermal energy
for power have also destroyed some geysers. Power plants in
New Zealand and Nevada have killed geysers as far away as twenty-five
miles. Hopefully, future geothermal power plants will be planned
so that there is no chance of the loss of any more of these
natural wonders. If future generations are to enjoy these unique
displays of nature, we must take great care to preserve them.
To see other geyser-related phenomena click to
Gallery of Geyser Field Formations.
Lee Krystek 2001. All Rights Reserved.