In Papua, New Guinea, lies the circular island volcano Manam, which is about 10 km (6 miles) across. It's a mildly active volcano, as you can see in this image from NASA's Earth Observing-1 satellite, taken in June 2009.

This is one of my favorite pictures of volcanoes from space, because it's almost seen straight down, the island is so nearly symmetric, and the plume so well-centered. It's exactly how I imagine these things should look from orbit!

Image credit: NASA