Volcanoes

Volcano – weak spot in Earth’s crust where molten material or magma comes to the surface.

Magma – molten mixture of rock-forming substances, gases and water from the mantle, when magma reaches Earth’s surface, it is called lava.

At plate boundaries, the crust often fractures due to the diverging (pulling) or convergent (pushing) plates. As a result, these fractures allow magma to reach the surface forming volcanic belts along the boundaries of Earth’s plates. One major belt is the Ring of Fire, formed by many volcanoes that rim the Pacific Ocean.

Island arc – string of islands created by volcanoes near boundaries where two oceanic plates collide and one sinks beneath the other. Hot spot – area where material from deep within the mantle rises then melts, forming magma; a volcano forms above a hot spot when magma erupts through the crust (ex. Hawaiian Islands).

Nonexplosive eruptions are the most common type of eruption. These eruptions produce relatively calm flows of lava. Nonexplosive eruptions can release huge amounts of lava. Vast areas of the Earth’s surface, including much of the sea floor and the Northwest region of the United States, are covered with lava from nonexplosive eruptions.

Explosive eruptions can be incredibly destructive. Instead of producing lava flows, explosive eruptions cause clouds of hot debris, ash, and gas to shoot out of the volcano, and molten rock to be blown into tiny particles that harden in the air. Ash can reach the upper atmosphere and can circle the Earth for years.

Inside of a Volcano

Inside a volcano is a system of passageways through which magma moves Inside a volcano is a system of passageways through which magma moves. This system includes a magma chamber, pipe, vent, lava flows and a crater.

Magma chamber – pocket where magma collects.

Pipe – tube that connects the magma chamber to Earth’s surface.

Vent – a smaller opening where magma leaves the volcano.

Lava flows – area covered by lava as it flows.

Crater – bowl-shaped area around the central vent.