Mehrdad1:
http://volcano.oregonstate.edu/oldroot/volcanoes/planet_volcano/venus/intro.html has an article entitled: "Volcanoes on Venus", which begins as follows:
"Volcanoes on Venus
"Overview
"Venus has more volcanoes than any other planet in the solar system. Over 1600 major volcanoes or volcanic features are known (see map), and there are many, many more smaller volcanoes. (No one has yet counted them all, but the total number may be over 100,000 or even over 1,000,000). These volcanoes come in a variety of forms. Most are either Large Shields or Smaller Shield volcanoes, but there are also many Complex Features, several Unusual Constructs, and a few Large Flow Features. None is known to be active at present, but our data is very limited. Thus, while most of these volcanoes are probably long dead, a few may still be active."
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AnTiFreeze3:
Actually, NASA's Magellan spacecraft used radar to map 98% of the Venusian surface, per the JPL webpage
http://www2.jpl.nasa.gov/magellan/ which begins as follows:
"Magellan MIssion to Venus
"Welcome to the Magellan Project home page!
"NASA's Magellan spacecraft made a dramatic conclusion to its highly successful mission at Venus when it is commanded to plunge into the planet's dense atmosphere Tuesday, October 11, 1994. During its four years in orbit around Earth's sister planet, the spacecraft has radar-mapped 98 percent of the surface and collected high-resolution gravity data of Venus. The purpose of the crash landing is to gain data on the planet's atmosphere and on the performance of the spacecraft as it descends.
"This home page offers Venus images taken by Magellan and other highlights from the mission."