Final answer:
The most significant difference between Earth's and Venus' volcanoes is due to the lack of plate tectonics on Venus, leading to unique volcanic features and a younger surface. Both planets have a similar elevation limit for mountains due to comparable gravitational strength.
Step-by-step explanation:
The key difference between the volcanoes of Earth and Venus lies in the mechanism that creates their respective geological features. Earth's surface is shaped by global plate tectonics, leading to a constant reworking of the planet's surface, whereas Venus lacks such tectonics. Instead, Venus features a form of 'blob tectonics' where hot material from below puckers and bursts through the surface, creating unique geological structures such as coronae and pancake volcanoes. Despite similar levels of volcanic activity, without Earth's plate tectonics, Venus has a younger-looking surface with mostly volcanic plains renewed by large flows of highly fluid lava.
When discussing elevation differences, both Venus and Earth have maximum differences of about 10 kilometers for their tallest mountains, not surpassing that limit due to the strength of gravity on both planets. Mars, with much lower gravity, supports the towering Olympus Mons, which is over twice the height of any mountain on Venus or Earth.