As if the hot temperature of Venus due to the greenhouse effect wasn't enough, Venus is also covered by evidence of global volcanism. The steep sided domes are evidence for high viscosity lava. Remember that the viscosity of a substance is increased if it contains abundant gas bubbles. Imagine releasing carbon dioxide under Earth's atmospheric pressure and then imagine releasing carbon dioxide under an atmosphere with 90 times the pressure. Gases remain trapped longer in the magma, and then are released explosively.
Coronae form a distinctive class of large volanoes on Venus.
They are characterized by large, concentric rings of fractures, ridges, and troughs. Evidence of upwelling of hot material, fracturing of the crust, and then collapse. Pancake domes are thought of form in a similar way. Wrinkle ridges are most common feature on the plains. The thick atmosphere is very sluggish at the surface.