Page "Caldera" Paragraph 18

Because there are no plate tectonics on Venus, heat is only lost by conduction through the lithosphere.

This causes enormous lava flows, accounting for 80 % of Venus ' surface area.

Many of the mountains are large shield volcanoes that range in size from 150 – 400 km in diameter and 2 – 4 km high.

More than 80 of these large shield volcanoes have summit calderas averaging 60 km across.