The largest is Olympus Mons, pictured above, which towers 22km above the surrounding plains – over two and a half times taller than Mount Everest.
This extinct volcano is 640km wide even at its narrowest point, greater than the distance between London and Glasgow, or Los Angeles and San Francisco.
It all serves to support the previous findings I mentioned about Martian volcanoes dating back upwards of 3.5 billion years.
The other reason for the massive size of Martian volcanoes is that Mars lacks active plate tectonics.
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