There they blow!

Topic: Geysers

Location: Yellowstone national park

Castle Geyser a couple of hours before sunset

As mentioned earlier, we are moving away from a epistolary format to a more topic based one, due to how we had to double back to see geysers and wildlife.

I understood the basics of hot pools reasonably well: as we go deeper into the crust, the water gets hotter. The warmer water transfers heat to the cooler water, raising the temperature and the pressure. The increased pressure causes the water to boil over. Mud pools are similar, except that dirt has mixed with the boiling water. 

Geysers were odd, because they have explosive episodes after which they are quiet. The basic physics is the same: water is heated at lower levels, and pressure builds leading to the explosion. But why don't they boil over continuously (i.e. why aren't they just hot pools?). I ended up looking up the mechanism; it requires that there are side pools to allow the pressure to build up. I found a nice explanation (via YouTube):

Getting all of these condition(side pools or "plumbing system", access to geothermal heated water, outlet to the surface) is somewhat difficult; this helps explain why geysers are so rare!

Old Faithful (erupts every 91 minutes)

Old Faithful Geyser

This is the most frequently geysers in the park.

Grand Geyser (erupts every 7.5 hours)

Grand Geyser

Of all the predictable geysers in the world, Grand Geyser has the tallest spray. The eruptions range from 150 to 200 feet at their maximum. Getting a good sense of scale was difficult; here is a failed attempt:

Attempt at scale for Grand Geyser. Note to others who want to try this; don't use a wide angle -- the nearby people look too large!

Morning Fountain (not predictable)

Morning geyser: Telephoto with people close gives a much better impression of scale

Castle Geyser (erupts every 13 hours)

A final image of Castle Geyser (from the top of post)