Old Faithful and Friends

 

            August 16 – We awoke to a clear day.  The fires were mainly on the east side of the park and a little north of where we were so the smoke wasn’t a problem.  After breakfast we noticed that one of the sites across the road from us had already been vacated and since it was much nicer than ours we moved our whole camp across the street.  We drove back to the west central part of the park to see Old Faithful and the other geysers and springs in the area.  As we approached the parking area Old Faithful went off, one of five eruptions we would see during the day.  The area around Old Faithful is fully developed with several hotels, lodges, lots of cabins, gift shops, convenience stores and a service station (believe it or not, fuel was more expensive in the park than it was in the remotest parts of Alaska!)  We found the visitor’s center, a small room unable to handle the waves of visitors streaming off of busses.  They were predicting eruptions of Old Faithful to be about 94 minutes apart (plus or minus 10 minutes).  Dave had visited Yellowstone around twenty years ago and he remembers eruptions being just over an hour apart and the brochures do say that the time between eruptions has been growing and often changes after earthquakes which are frequent.  There are several major areas of geysers and springs with boardwalks within a few miles of Old Faithful and visited them all.  We saw Old Faithful erupt once up close and while we toured the geysers around it we saw erupt in the distance several times.  We were lucky and saw three other major geysers erupt.

            How do the hot springs and geysers work?  Well a lot of Yellowstone Park is actually on top of a dormant volcano.  The volcano last erupted around 640,000 years ago and following the eruption the cone of the volcano collapsed and created a giant round valley.  Since the valley is on top of a volcano the earth’s crust is very thin (relatively speaking) and the heat from the core of the earth reaches up and heats up the ground water.  Once the boiling point of the water is reached steam forms and its pressure forces the water through cracks in the ground to the surface creating hot springs.  Over thousands of years the hot water dissolves the surrounding limestone and turns those cracks into passageways and chambers underground.  A geyser is basically a hot spring with a blockage that prevents the water from continually reaching the surface creating pressure underground which eventually forces the blockage out of the way.  A unique set of features must coincide to create a geyser.  The first requirement is lots of water which is abundant because of all the snow that is received in the winter.  The second ingredient is lots of heat which is supplied by the nearby magma under the earth’s crust.  The heat travels through the rock and heats the water.  In a hot spring the heated water and steam flow up from the chamber where they were heated to the surface through passageways carved by the water, but a geyser has one final requirement – a constriction.  The constriction is a narrow spot in the passageway that leads from the chamber to the surface.  A constriction can be created suddenly by an earthquake which shifts a passageway.  A constriction may also be created slowly as the limestone carried by the water is deposited on the sides of a passageway.  Once a constriction is created some of the heated water still flows to the surface, but some of it also tries to find a new route to the surface and runs through other cracks in the ground.  If conditions are right the water cools as is explores these other cracks and it deposits the limestone it is carrying, effectively sealing off the crack.  Over time enough of the cracks are sealed off that the major route to the surface is through the constriction.  When the water reaches the surface it cools and the cooler water is heavier than the hot water so it tries to flow back down into the heating chamber.  A bottleneck develops at the constriction and the weight of the cooler water creates a plug which keeps the hot water from rising up.  With the flow of hot water blocked the rest of the water above the constriction cools down, making the plug even stronger.  Small steam bubbles are still able to escape, but they don’t have enough power to clear the blockade.  Meanwhile, the heating chamber is still heating water and since the heated water can’t get past the bottle neck it just keeps getting hotter.  As the water gets hotter, more of it turns to steam creating bigger bubbles.   The steam bubbles continue to escape until they reach a point where they are so big that they can’t fit through the constriction.  At this point the system is totally plugged up and nothing escapes to the surface.  The water keeps on heating and the pressure continues to build up.  The pressure gets so great that the water is prevented from boiling and steam stops forming even though the temperature is above the boiling point.  The water is said to be superheated at this point.  The temperature and pressure keep rising until the point is finally reached where the extreme pressure blasts the steam bubbles and cooled water out of the constriction and the eruption begins.  The superheated water in the chamber, being relieved of the pressure, instantly boils and starts to turn to steam.  This steam creates more pressure which blasts water to the surface.  The water keeps boiling and blasting until all of the water has boiled and there is no pressure left in the system at which point the eruption ceases.  The whole cycle then starts all over again.

            How long the process takes is dependant on the nature of the underground plumbing system.  Systems with more heat and water will generally erupt more often.  Many different geysers and springs are connected by passageways and what happens at one affects the others, making predicting them difficult.  Earthquakes, which are small, but common (over 1,000 a year) are also constantly creating changes in the ground which may create new passageways or close existing ones. Many geysers have gone dormant after some earthquakes while others will become more active.  Hot springs can also turn into geysers as a result of earthquakes.   Old Faithful is relatively predictable because it is not near any other hot springs or geysers and has a constant flow of incoming water.  There are many smaller geysers that erupt every ten minutes or so while others may have years between their eruptions.

            There are several major geysers around Old Faithful and we were lucky and say three other major ones erupt.  One of them, Riverside geyser was a big treat because it is at the edge of the river that drains the geyser basin and when it erupts it shoots water over the river creating great rainbows.

            Check out the Hot Springs & Geysers link for more pictures!