You will be visiting Andrews Geyser. This is a manmade fountain
that uses gravity to force water from a lake two miles away (and
500 feet higher in elevation) down a pipe that decreases in
diameter, thus producing a fountain over 100 feet in height. The
fountain is usually only "on" during daylight hours. Though not a
naturally occurring phenomenon this EarthCache exists to educate
cachers about geysers, which are pretty darn rare in western North
Carolina. (The photos on the cache page are of Old Faithful in
Yellowstone.)
Imagine yourself exploring a desolate, rocky region in Iceland
or Yellowstone National Park, minding your own business and
admiring the volcanic formations around you. The ground is
relatively flat but covered in mounds of yellow and white material
with a vague but distinctive smell of rotten eggs. The entire area
is mysteriously foggy, framed by trails of vapor rising from cracks
in the earth everywhere you look. Suddenly, steam and hot water
burst out of the ground in a spectacular fountain that lasts for
several minutes, reaching hundreds of feet in the air and making a
roar like a freight train speeding right past you. Just as quickly
as it began, though, the event ends, leaving small pools of
steaming water in a wide circle around the vent.
What you would have witnessed is a geyser eruption, one of
nature’s most impressive displays of hydrothermal energy. They
occur where magma lies just below the earth’s surface, particularly
in volcanic regions such as Iceland or New Zealand, and places that
have been volcanically active in the past, including Yellowstone in
Wyoming. Water from rain or melted snow percolates into the ground
through cracks and fractures and interacts with the hot underlying
rocks. The water reaches temperatures far above where it would boil
on the earth’s surface (about 100 degrees Celsius), but because
there is so much rock above the water (sometimes up to several
miles), the water does not boil. Instead it becomes superheated and
pressurized. Once enough pressure builds up, the superheated water
will overcome the weight of the overlying rocks and burst out of
the ground in an explosive steam eruption—a geyser. It basically
works like a teapot with a closed lid; only when enough pressure
builds up from accumulating hot water and steam is there enough
force for the steam to burst out through the top and activate the
whistle.
One of the most fascinating aspects of geysers is that once they
form, they become self-perpetuating. After the initial eruption of
hot water, the pressure on the superheated groundwater is reduced,
which causes some of it to flash to steam (when you reduce pressure
on a liquid, it becomes easier for the individual molecules to
escape into the vapor phase--even without an increase in
temperature). Because it is a gas, the steam expands rapidly,
causing it to burst upward through the small, tight fractures in
the rock, forcing out any hot water that was left behind after the
initial blast. Once the channels are empty, the eruption ends and
the cycle begins anew. More water seeps into the hot areas along
the fractures, heats up and starts building pressure all over
again.
Some geysers go through the pressure-building cycle quickly,
producing fountains every few minutes. Old Faithful in
Yellowstone—one of the most famous geysers in the world—puts on its
show approximately every 80 minutes and can reach up to nearly 200
feet in height. If you observe Old Faithful in action for several
eruptions, you can begin to see how the pressure-building process
plays a role in its behavior. When the eruption is short (less than
about two minutes in length), the next blast usually happens within
about 45 minutes, a relatively short interval of inactivity for
this geyser. But when the eruption is more powerful (up to five
minutes long), it will take more time for the pressure to reach the
critical level, and you could be waiting nearly an hour and a half
for the next event.
Other geysers are not such reliable performers and have not
erupted in years, such as Steamboat, also located in Yellowstone.
Often, however, these infrequently erupting geysers can be some of
the most spectacular when they do finally burst into action.
Steamboat, for instance, has been known to produce blasts extending
nearly 400 feet in the air, one of the largest in the world.
There are hundreds of geysers around the world—estimates are up
to 700—and Yellowstone boasts nearly half of them. The name
"geyser" comes from the Icelandic word "geysir," for "gush," and
the original namesake is found in Iceland, in the Haukadalur Basin.
Unfortunately, it only erupts occasionally, which illustrates
another important point about geysers. They are ephemeral features,
usually only lasting for several thousand years or until a major
geologic event occurs. For instance, an earthquake of magnitude 6.1
in 1975 in the Norris Geyser Basin of Yellowstone caused greater
water volumes to flow in some geysers and decreased the activity of
others by rearranging groundwater paths and fracture patterns
throughout the area. Even earthquakes as small as magnitude 4 can
change the behavior and eruption intervals of geysers. Moreover, it
turns out that earthquakes may be necessary to keep some geysers
active. Over time, water conduits feeding geysers can become
narrower or even clog as a result of deposition of minerals from
the hot water (just like pipes can clog in areas with hard,
mineral-rich water). Frequent tremors may break up the deposits or
create new fractures, providing alternative pathways for the water
to move through the rock and keep the geysers supplied.
There are three requirements to log a Found it for
this Earthcache:
1. Post a photo of you and/or your group -- with a GPSr --
showing the "geyser" found at the listed coordinates.
2. Estimate the height of the "geyser." Email me your answer and
the technique you used to make your estimation.
3. Email me two ways that this "geyser" is different from the Old
Faithful found in Yellowstone National Park. (The fact that one is
in NC and the other in WY is a given so please try to come up with
a different difference.) Do NOT include your answers in your online
log.
For more information on EarthCaches please click
here.
Online logs that do not fulfill all three requirements -- email
answer to questions and an uploaded photo -- will be deleted.
Photos used on this cache page are of Old Faithful in
Yellowstone.
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