[Geysers] Constrictions, bubbles, and pressure

[jacross]

Here is an interesting experiment.  I believe it shows that when a bubble 
rises through a constriction in 
a geyser system, the pressure drops briefly.  If the pressure drops, the 
boiling rate should increase, and 
this might trigger an eruption.

1) Obtain 4 feet of tygon tubing, surgical tubing, or similar material.
2) Fill it with water.
3) Get a bubble situated in the middle of the tubing section.
4) Now hold both ends open, vertical, and next to each other.  The bubble will 
rise up one side of the U 
tube.
5) The water level in the side containing the bubble will be highest.
6) Pinch the tubing above the bubble so that the bubble must flow through the 
constriction on its way 
to the surface.
7) Note that the water levels change while the bubble is flowing through the 
constriction.  The low side 
gets lower, but it rebounds once the bubble has passed through.

I suspect this last observation means that the pressure dropped while the 
bubble moved through the 
constriction.  Why this happens isn't clear to me.

I welcome explanations.

I must get back to doing something productive.

Have fun.

Jeff Cross
jacross at lamar.colostate.edu