What are Volcanos?
Volcanoes are mountains or hills that form due to accumulation of materials erupted through openings in the earth’s surface. These openings are called volcanic vents. While most volcanoes have steep sides, some can be plateaus or plains.
Mt. Saint Helens
How are volcanoes formed?
Volcanoes are formed by the accumulation of magma. Magma is the molten rock that flows from below the earth’s surface. Magma flows from the volcanic vents, which can be a single opening, a cluster of openings, or a long crack. Volcanic vents form deep within the earth in the upper part of the mantle. When tiny droplets of magma are formed they begin to rise because the magma is less dense than the solid rock surrounding it. It usually does not go directly to the surface, but instead it accumulates in storage areas, called magma reservoirs, before it spills onto the surface. After every eruption, after the magma dries it forms a new layer on the volcano.
What materials come out of a volcano?
There are three different types of materials that can flow from an active earthquake. The first is Lava, which is the magma that escapes to the surface. It is hot and bubbly, and is named according to its texture. Lava flows that are smooth and continuos are called pahoehoe (pronounced pah hoh ee hoh ee). Lava flows made of chunks of lava or have a jagged surface are called aa (pronounced ah ah).
The second material is called Tephra. Tephra is made of rock fragments formed by the explosion of sticky magma. The term tephra itself means any airborne pyroclastic (fire-broken) material regardless of size and shape. The most common Tephra materials are pumice, cinders, and volcanic ash.
Finally, there are gases released from the volcano during an eruption. They are mostly in the form of steam. The gases are usually caused by the magma itself or the magma coming in contact with water on the ground. Most volcanic gases are made of water vapor, carbon dioxide, and sulfur dioxide, and occasionally chlorine and fluorine gases.
What are Explosive and Non-explosive eruptions?
Explosive eruptions can eject liquid and semisolid lava as well as solid fragments of volcanic rock. They also throw lots of material into the air. In non-explosive eruptions, such as Hawaiian volcanoes, lava is only produced. Tephra is rarely ejected in non-explosive eruptions.
What kinds of volcanoes are there?
The first two kinds of volcanoes are Cinder cones and Composite Volcanoes. They are the familiar cone shapes that we associate volcanoes with. Cinder cones are primarily smaller than composite volcanoes because they involve weaker explosions, small volume eruptions that do not stray far from the vent and they usually have a short life, as they can become extinct after one eruption. In some composite volcanoes after a major eruption, nonexplosive extrusions of lava within the summit crater can later construct a bulbous mound of accumulated lava, called a lava or volcanic dome.
Cinder Cone Volcano
Another kind of volcano is a Shield volcano. Shield volcanoes get their name from their distinctive, gently sloping mound shape that resembles an ancient shield. Their shape is caused by many nonexplosive eruptions that pour out lava.
A third kind of volcano is called a caldera. A caldera is a round or oval shaped low-lying area that forms when the ground collapses after an eruption. Some calderas can be seen in Yellowstone National Park and in Long Valley, California. Crater Lake in Oregon is an example of a water-filled caldera.
Crater Lake
Finally, another place volcanoes can be found is on Volcanic Plateaus. These are the largest volcanoes on earth, yet they do not look like volcanoes. The plateaus are vast, nearly flat-topped accumulations of erupted materials. The plateaus can cover thousands of square kilometers.
Volcanoes are most common on the edges of plate boundaries and are most common in the Ring of Fire (see earthquakes).