Volcanic ash and weathered basalt produce some of the most fertile soil in the world, rich in nutrients such as iron, magnesium, potassium, calcium, and phosphorus.

More than 450 volcanoes are located in the Pacific Ocean basin, forming a ring known as the Ring of Fire.

Mount Etna of Italy is thought to be the world's oldest active volcano. The first record of its eruption dates back to 1500 BC. Since then, Etna has erupted 190 times.

At present, about 800 million people live within 100 km of an active volcano--a distance well within reach of potentially lethal volcanic hazards. Of these, about 200 million are in Indonesia.

It is difficult to distinguish an extinct volcano from a dormant (inactive) one. Dormant volcanoes are those that have not erupted for thousands of years, but are likely to erupt again in the future. A volcano is often considered to be extinct if there are no written records of its activity.

Jupiter's moon Io is the most volcanically active world in the Solar System, with active volcanoes constantly spewing material onto Io's surface, some erupting lava fountains up to 250 miles high.

Olympus Mons on Mars is large shield volcano that stands about 21 km (13 mi) tall--a little over twice the height of Mauna Kea, Earth's tallest volcano, as measured from its base on the ocean floor.