What Are Shield Volcanoes?

Shield volcanoes are basically fluid lava flows. Flow after flow pours out in all directions from a central summit vent, or group of vents. This builds up a broad, sloping cone that looks a bit like a warrior's shield. They are built up slowly by the thousands of flows of basalt, a hard, dense dark volcanic rockand the lava spreads over great distances. Some of the largest volcanoes in the world are shield volcanoes.

Mauna Loa, the largest of the shield volcanoes (and also the world's largest active volcano), projects 13,677 feet above sea level, its top is over 28,000 feet above the deep ocean floor.

The planet Mars has a lot of huge shield volcanoes. Some of these are so big they are a hundred times bigger than all of the Hawaiin volcanoes put together. The shield volcanoes on Mars are bigger but they look very similar. They are also a lot older than those on Earth – Martian shield volcanoes are between 20 and 200 million years old.