Tharsis Rise could be solar system's biggest volcano

This article is about a massive volcano on Mars which is thought to be the spreading type like Etna.
While not as tall as Olympus Mons, it is said to be bigger at a huge 7000km across.
So if Mars geology is similar (but on a much smaller scale) to Earth's geology, then there must be many other similarities too you would think.

There are plenty of similarities between the two volcanoes, despite the discrepancy in scale – Etna is around 200 times smaller. Tharsis is surrounded by titanic gouges in the landscape radiating outwards for hundreds of miles, known as fossae. The biggest of these structures, Valles Marineris, averages 4km deep and stretches some 4000km. On a smaller scale, comparable faults radiate into the landscape around Etna. Both Etna and Tharsis show similar patterns of rifting running through the body of the volcano. And the basic proportions of the two structures are surprisingly alike.

I think this warrants futher discussion from those in the know of volcanoes. Maybe you would enlighten us as to the processes which formed Etna?
planetearth.nerc.ac.uk...

reply to post by zenius

But who knows what lies beneath the clouds of Venus?