Yellowstone National Park, July 2006
Jewel Geyser has short (lasting 1 or 2 minutes), frequent (occurring every 5-10 minutes) eruptions, that spray water between 15 and 30 feet high.
As I was walking past the geyser it was quiet, so I took a close-up photo of it. After a few minutes wait, my patience was rewarded with this eruption.