Volcanic bulges that resemble giant spiders provide more evidence that Venus' landscape is shaped by huge blobs of molten rock rising from inside the planet, say Magellan spacecraft scientists.

The bulges, some more than 100 miles wide, support the theory that Venus' terrain is sculptured by "hot spot tectonics" or "blob tectonics," NASA geologist Ellen Stofan said Wednesday. In that process, large underground plumes or blobs of molten rock flow to the planet's surface.A similar process created the Hawaiian Islands. But the dominant geological force on Earth is known as "plate tectonics," or continental drift. Gargantuan plates of Earth's crust drift across the planet, colliding to create mountain ranges such as the Himalayas.

Scientists named Venus' bulges "arachnoids" because they look like spiders, which belong to a class of animals called arachnids.