Final answer:
The smallest type of volcano typically has a symmetrical shape with a deep crater and is known as a cinder cone volcano. While the provided text focuses on Venus and Mars' geological features, cinder cone volcanoes are the smallest and comparable to those found on Earth.
Step-by-step explanation:
The smallest type of volcano, often symmetrical with a deep crater, is referenced in the context of Mars and Venus' geology. While not explicitly named in the provided excerpts, a cone or cinder cone volcano, commonly found on Earth, fits this description. These small, steeply sloped volcanoes are built from particles and blobs of congealed lava ejected from a single vent.
As the lava is blown into the air, it breaks into small fragments that solidify and fall as cinders around the vent, forming a circular or oval cone. Despite the provided information focusing on Venus and Mars, where features such as pancake domes and the massive Olympus Mons dominate, the cinder cone volcanoes similar to those on Earth likely represent the smallest volcanic structures on those planets.
Venus, for instance, has thousands of smaller volcanoes down to the limit of visibility of the Magellan images, comparable in size to terrestrial equivalents.