Section 10-1 What is a volcano? Describe the process that causes a volcano. Define vent and crater. Explain the three kinds of places that volcanoes are likely to be found.

A volcano is an opening in Earth’s surface that forms a mountain when layers of lava and volcanic ash erupt and build up. Most of Earth’s volcanoes are dormant, which means that they are not currently active. Active volcanoes sometimes spew steam, smoke, ash, cinders, and flows of lava.

What Causes Volcanoes? Volcanoes occur when magma, which is less dense than the rock around it, is slowly forced upward towards the Earth’s surface. After many thousands or millions of years, lava flows out through an opening in Earth’s surface. As the lava flows, it cools and becomes solid, forming igneous rock.

A vent is an opening in Earth’s surface through which lava, ash, cinders, smoke, and steam can flow. A crater is the steep-walled depression around a volcano’s vent.

Crater

Volcanoes can occur at divergent boundaries which are areas where Earth’s plates are moving apart. Where the plates separate, they form long, deep cracks called rifts. Iceland was made from a rift on the Mid-Atlantic Ridge.

Volcanoes can also occur at convergent boundaries which are areas where Earth’s plates move together. When plates converge, one plate slides under another plate where the plate melts and is forced upward in a volcano.

Examples of volcanoes formed by convergent boundaries are found around the Pacific Plate, which is known as the Pacific Ring of Fire.

Lastly, volcanoes can occur at hot spots, areas in Earth’s mantle that are hotter than neighboring areas, forming melted rock that rises toward the crust. The Hawaiian Islands were formed from hot spots.