Craters and Volcanoes
The surface on Venus is literally a storybook of its very diverse and interesting history. It is scattered with a variety of craters created from multiple asteroids and meteorites. Due to the thick atmosphere, it is unusual to find any small craters two kilometers (1.2 miles) or less on the surface because they usually burn up and or disintegrate into much smaller pieces. Sometimes larger meteorites break up into smaller pieces before impact and create crater clusters.
In addition the surface is also heavy with Venusian volcanoes of all shapes and sizes. At least 85% of Venus's surface is composed of volcanoes and volcanic rock. The history of Venus's heavy terrain dates back almost 800 million years when the planet violently reformed its surface due to heavy volcanism that wiped out any previous craters. Now Venus has over 100,000 small shield volcanoes with hundreds of large volcanoes. Lava flows from the volcanoes carved long canals that extend up to 7,000 kilometers (4,300 miles).
Magellan's imaging provided a vast amount of data that showed a large variety of other volcanoes such as pancake volcanoes, coronae and archnoids. Pancake volcanoes are formed by eruptions of very viscous lava and cooling into large flat patty-like shapes. Coronae are large, round features that seem to be large collapsed domes over magma chambers. Characteristics include a circular border of cliffs, extending hundreds of miles across. The archnoids are similar in shape to the coronae but are formed when molten rock fills gaps and fractures on the surface of Venus. Also very prevalent on Venus are giant calderas that extend in lengths greater than 100 kilometers (62 miles).