![Image](http://earthobservatory.nasa.gov/images/imagerecords/38000/38985/ISS020-E-09048.jpg)
...In contrast, the smooth white cloud on top may be water condensation that resulted from rapid rising and cooling of the air mass above the ash column. This cloud, which meteorologists call a pileus cloud, is probably a transient feature: the eruption plume is starting to punch through. The structure also indicates that little to no shearing wind was present at the time to disrupt the plume...