New Page 2

Geysers

Basic Requirements | Water Cycle in a Geyser | Geyser Types | Irregular and Regular

When you hear the term "geyser" most peoples minds instantly think about the worlds most famous geyser, Old Faithful. Geysers jet water above the ground, sometimes up to 200 feet into the air. These eruptions are magnificent, but have you ever wondered how geysers work?

Basic Requirements
    First you need some basic requirements: a heat source, a water source and constricted and complicated plumbing.

    Yellowstone's Heat Source
    The extremely hot volcanic rocks below Yellowstone's geyser basins provide the intense heat need to produce the eruptions. These rocks are continually heated when there is magma or molten rock a few miles below the surface.

    Yellowstone's Water Source
    Snowmelt from the surrounding mountain ranges and rainfall soaks into the ground. This water flows into the geyser basins as ground water, however it becomes heated as it travels further down.

The Plumbing
All geysers have a surface vent connected to a pipe like crack. (In order for a geyser to form there has to be a constriction in its plumbing.) This "pipe" goes down into some hot rocks and then widens, forming a chamber. Then from this chamber several other narrow cracks go down deeper. These collect the water that feeds the geysers eruptions.

Yellowstone's geyser basins contains about 500 geysers. That's half the number of geysers in the world! Many places have hot springs but as you have learned geysers can only be in places with specific conditions.

Move Mouse Over to see where the world's geyser fields are.

The Cycle of Water in a Geyser [Back to Top]

(this cycle will start just after an eruption)

Geyser Eruption Process : Stage 1 1) The vent and crack have been mostly emptied of water. Some of this water will fall directly back into the vent. Of course being much cooler.
2) Water begins seeping into the cracks from the sides. This water is already quite hot from being heated by the volcanic rocks.
3) More water enters the crack and the water level slowly rises towards the surface. This new water adds weight creating more pressure on the water below it.

Geyser Eruption Process : Stage 2 4) This pressure prevents the water from boiling even though it is much hotter than the boiling point. The pressure builds and pushes some water so that it overflows onto the surface surrounding the geyser.
5) That relief from pressure allows the super heated water below to flash into steam. (Remember that steam takes up thousands of times more space than water does.)

Geyser Eruption Process : Stage 3 6) This flash creates a massive surge of pressure through the constriction in the narrow passage. This is what sends the water shooting into the air.
Then the cycle begins again.

Above diagrams adapted from Hays.outcrop.org

Geyser Types    [Back to Top]
Cone-Type Geysers:
    Most well known geysers are the cone-type. Just below the ground is a very narrow constriction. Many cone-type geysers spray a bit of water during the time in between eruptions, this constant wetting is what created and caused the cone to grow larger.
    This small opening acts like a nozzle during the main eruption. Cone-type geysers are very forceful, jetting steady streams of water to great heights. This is why many of these geysers are famous; geysers such as Old Faithful and Castle Geysers are in this category.

Move Over to see an example of a cone geyser. (Source: Sarah Walinga)

Fountain-Type Geysers:
    The other kind of geyser is the fountain-type. They have a large open crater at the surface that fills with water before and during the eruption. Since the steam the allows the geyser to erupt it must first rise to the surface, in a fountain-type geyser it has to rise through the pool. This creates separate splashes which make bursting and spraying eruptions.
    These fountain-type geysers are much more common than cone-type geysers. Nearly all smaller geysers along the trails in Yellowstone's geyser basins are examples, and it is similar in geyser fields around the world. However, they can be very large; like Grand and Great Fountain Geyser in Yellowstone.

Move Over to see an example of a fountain geyser.

Irregular and Regular       [Back to Top]
    Most tourist attractions in the park surround regular geysers, meaning that the times that they erupt are consistent and predictable. They can be kept track of based on the discovery that the amount of time between eruptions is directly related to how long the previous eruption lasted for. This is because longer eruptions use up more water, thus it takes longer to refill the underground channels.
    Irregular geysers are the most common. The have no set schedule and are impossible to predict.
    A regular and predictable geyser can be quickly rendered irregular, as many earthquakes occur in the park each year. These quakes can change the plumbing of a geyser, which in turn can remove the crucial constriction needed or even cut off the geysers water supply.

	1) The vent and crack have been mostly emptied of water. Some of this water will fall directly back into the vent. Of course being much cooler. 2) Water begins seeping into the cracks from the sides. This water is already quite hot from being heated by the volcanic rocks. 3) More water enters the crack and the water level slowly rises towards the surface. This new water adds weight creating more pressure on the water below it.
	4) This pressure prevents the water from boiling even though it is much hotter than the boiling point. The pressure builds and pushes some water so that it overflows onto the surface surrounding the geyser. 5) That relief from pressure allows the super heated water below to flash into steam. (Remember that steam takes up thousands of times more space than water does.)
	6) This flash creates a massive surge of pressure through the constriction in the narrow passage. This is what sends the water shooting into the air. Then the cycle begins again.