Travel Reference
In-Depth Information
Figure 2. How does a geyser work?
• The boiling temperature of water is higher at higher pressures. The weight of a
column of water raises the pressure at the bottom, which raises the boiling tem-
perature. This lets the hot rocks raise the water temperature, making it super-
heated water.
• The same weight of water occupies far more space as steam than it does as liquid
water—on the order of a thousand times more space.
• Superheated water flashes into steam if the pressure on it is lowered to ordinary
atmospheric pressure.
Now back inside the geyser:
3. As more water enters the crack (or
fissure),
the water level rises toward the surface. The
added weight of water increases the pressure near the bottom. The hot water heats the
somewhat cooler water already in the fissure. The water level rises past the very narrow
parts of the vent.
4. As the superheated water continues to rise in the fissure, it starts to boil gently, forming
small steam bubbles that rise and heat the overlying water. Because the deeper boiling wa-
ter is under higher pressure, it boils at higher temperature, and its steam heats the upper
water to its boiling point. More bubbles form, raising the column of water and bubbles in
the fissure until it reaches the surface at the vent. Up to this point, the water pressure at
depth has been increasing.
5. When water starts to spill out of the vent, the column of water in the fissure is at its
greatest height. More steam bubbles from below displace liquid water, some of which
spills out at the top. With more steam bubbles in the column now, the weight of the water
becomes less, more boiling occurs, even below the constricted parts, and water comes out
faster.
6. Next, the steam from below rushes through the constriction like jet engine exhaust. The
water is being pushed rapidly toward the surface and spurts out. As more superheated
water rises to the upper part of the water column, far more bubbles form, so the column
has far more steam in it and thus less weight. This greatly reduces the pressure inside,
letting the steam blow the water column out of the vent. The geyser is erupting—an ex-
ponentially accelerating catastrophe!
7. When all the steam has managed to escape from below the constriction, there's nothing
more to push on the water, and not much water there, so the eruption stops. Then the
cycle begins again.
There's more about geysers in the Geological History chapter.
