Yellowstone is an amazing place with a geology that is not found in many other places on the planet.  A substantial portion of Yellowstone sits on top a very old super volcano.  The magma from that super volcano is relatively close to the surface and is warm enough to heat the ground water causing hot springs and geysers to form, Old Faithful being one of them.  As part of the workshop I attended, run by Hudson Henry (HudsonHenry.com), we visited several hot springs as they present a fantastic photography opportunity. The first originally wasn't part of the planned schedule.  Entering the park from Gardiner, where we stayed, you had to pass thru the Yellowstone Justice Center and you'll likely ride past Mammoth hot spring.  From the road this mountain of a hot spring looks about as inviting and interesting as a Penn DOT mountain of winter road rock salt.  It has been formed over time by the deposits left behind by the boiling water that bubbles up from the ground below.  We ended up spending time here because Rebecca, one of the photographers in the group, had shared a picture she took there on a side trip she made, and it was amazing.  So, plans were changed, and we did some recon of Mammoth Springs on Sunday night for a possible return in the morning when the light would be better.  We drove to the far side of the springs where the water from below was running and indeed there were photographs to be had.  As pretty as the hot springs look you will notice they are quite toxic to plant life.  Visitors are required to stay on the provided walkways. Even though it was the evening and the springs were in the shade of the mountain towering above to the west, the images I got that night are some of my favorites.

That night we were going to another hot spring for sunset pictures but that plan was spoiled by a lack of clouds in the sky and getting to the location a little to late so we attempted some "blue hour" and light painting at another hot springs that was on the way.  Like everywhere else we had to stick to the acceptable path but here it was considerably closer to the springs.
The next morning, we were up before sunrise and headed back to Mammoth springs to get some photographs lit by the early morning light when there was a good chance the steam would enhance the images even more.  When I saw the moon rising in the sky ahead of the sun I had to stop and take the shot even though our destination was beyond the boardwalk you see in the picture.  It was really the first time we saw the moon when I was able to have a camera in my hand.  The morning light did not disappoint.
This Monday was to become Hot Springs Day as the plan was to go to Grand Prismatic hot springs in the afternoon on the way to dinner with Old Faithful and then a sunset at yet another hot springs area called Paint Pots.  Grand Prismatic Springs was, well, grand.  It was a good place to be in the late afternoon as the best images were on the ground and for a change the sunlight brought out and magnified the colors bubbling up from the ground.  
Next it was on to Old Faithful.  I was struck by how much the park had done to accommodate what must be a enormous amount of visitors the geyser must get for what amounts to about a 10min show.  The parking was Disney-esk except you didn't have to pay extra.  The geyser has stadium seating in a half circle where folks sit and wait for it to erupt which happens about every 60 to 90 minutes.   It gave us a head fake, it started and then quit.  I thought wow, will we have to come back? Then in a moment or two it did its thing for about 3 min. When it was done the place emptied out and a new group comes in for the next eruption. I threw all the images into a timeline collage.  
If you are interested in learning more about how the Yellowstone Caldera was formed I would suggest doing a you YouTube search for Yellowstone + GeologyHub.  They have posted an explanation of how the Yellowstone Caldera was formed that includes some images of the springs from viewpoints you can't get as a visitor.    

For more of my Yellowstone images, click here: 

Yellowstone Wild Life      Yellowstone Sunrinse Sunsets and In Between     Yellowstone - Grand Tetons