This is an image of "puddle-like" flows of Europa taken by the Galileo spacecraft. This image is called "the mitten".
Click on image for full size
The picture seems to show the presence of a "puddle" which has seemingly wiped out the surface nearby. Scientists cannot prove that this feature is really the remnants of a puddle, but such a patch probably involves a local pocket of water which refroze on the surface.
This feature suggests a third process, one which scientists call icy-volcanism. In this case, even though a volcanic cone is not formed, a liquid comes out of the ground and flows on the surface. That is why this feature is called icy-volcanism.
You may leave the tour and read more about terrestrial volcanism and how volcanic cones are formed on Earth using the link at the bottom of the page.
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