This image was produced by the 3D imaging of Magellan. Vertical scale is greatly exaggerated. There are two pieces of evidence that point to volcanism still taking place on Venus. Levels of sulfur dioxide in the atmosphere show variations. One spacecraft measured very high levels of sulfur dioxide but levels dropped off over time.
Sulfur dioxide is a gas commonly released in volcanic eruptions.
On Earth, when a volcano erupts, our atmospheric levels of this gas rise. Another bit of evidence is that two orbiters have measured bursts of radio energy on Venus. These bursts are similar to those produced by lightening discharges which often occur in the plumes of erupting volcanoes. These volcanic lava domes are found on the southeast edge of Alpha Regio. They occur when molten rock emerges out of the ground and then retreats, leaving a thin solid crust such as this.