A sign of bad weather in the distance:
Olympus XZ-1, 50mm, ISO100, f8, 1/1250s
These clouds sometimes just pop up in summer on otherwise sunny days, and you can observe them expand upwards; they can grow to over 15 kilometers in height.
Very nice to look at they may be, but they are not so nice to stand under, as they often produce thunderstorms, heavy rain, and strong winds.
There's a colour version of this photo on this Dutch Wikipedia page, but don't worry about my having stolen it; I put it there.
Thanks for watching!
Previous entry: Cloudburst.