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VOLCANOES
INTRODUCTION
Welcome to the wonderful world of volcanoes! Volcanoes are openings in the Earth's surface that often forms a mountain when layers of lava and volcanic ash erupt and build up. Most of Earth's volcanoes are dormant, which means they are not currently active.
CAUSES OF VOLCANOES
Magma forms deep inside the Earth. Heat and pressure cause rock to melt and form magma. Some deep rocks are already molten, and others are hot enough that a small rise in temperature or drop in pressure can melt them to form magma.
Magma is less thick than the rocks around it, so the magma is forced upward very slowly towards the surface of the Earth. After many years, maybe even millions, magma reaches Earth's surface through an opening called a vent. As lava flows out, it cools quickly and becomes solid. This forms layers of igneous rock around the vent. The steep walled depression around a volcano's vent is the crater.
WHERE DO VOLCANOES OCCUR?
Volcanoes form in three kinds of places. These are all directly related to the movement of Earth's plates. They occur where plates are moving apart, where plates are moving together, and locations called hot spots. Hot spots are areas in the Earth's mantle that are hotter than the neighboring areas, forming melted that rises towards the crust.
1.DIVERGENT BOUNDARIES
An example of a divergent plate boundary is the Mid-Atlantic Ridge. At this ridge, the Earth's plates are moving apart. When these plates separate, they form long, deep cracks called rifts. Magma flows through these rifts as lava and is quickly cooled by the ocean's water. As more lava flows, it builds up from the bottom of the ocean. Sometimes the volcanoes and rift eruptions rise above the top of the ocean and form islands.
2.CONVERGENT BOUNDARIES
Earth's plates move together at convergent boundaries.
An example of a convergent plate boundary is the Cascade Mountain Range of Oregon and Washington in the northwestern United States. When these plates move together the part that slides underneath another plate is partially melted forming magama. The magama is then forced up to the surface forming volcanoes.
HOT SPOTS
Geologists believe that some areas in Earth's mantle are hotter than other areas. Some geologists believe that hot spot magma is formed at the mantle-outer core boundary. These hot spots melt rock which is then forced upward towards the crust as magma. Hot spots are areas in Earth's mantle that are hotter than areas around them, forming melted rock that rises to the crust.
TYPES OF ERUPTIONS
There are three different types of eruptions. There are violent and explosive, quiet, and some volcanic eruptions are both violent and/or quiet. Two important things that determine whether an eruption will be explosive or quiet: 1. The amount of water vapor and other gases that are trapped in the magma. 2. If the magma is basaltic or grantic.
FORMS OF VOLCANOES
There are three types of volcanoes. They are, shield, cinder-cone, and composite volcanoes. Shield volcanoes have quiet eruptions and basaltic lava. Cinder-cone volcanoes have explosive eruptions that throw lava high in the air. Cinder-cone volcanoes are formed by volcanic ash called tephra. Tephra can be very small or large rocks. When tephra falls to the ground it forms a steep sided, loosely consolidated cinder-cone volcano. Composite volcanoes vary between loud and explosive eruptions and quiet eruptions. When a composite volcano violently explodes it can release gas and ash forming a tephra layer. Then when a quiet eruption occurs, lava hardens over the tephra layer. When this alternation between lava and tephra is repeated over and over in alternating layers, it forms a composite volcano.
BATHOLITHS
Batholiths are the largest intrusive igneous rock bodies that form when magma cools and becomes solid underground, and stops rising to the surface. Some batholiths are not hidden in the Earth. Some have been exposed at Earth's surface by erosion.
DIKES AND SILLS
Magma that is usually squeezed into a vertical crack that cuts across rock layers and hardens is called a dike. Magma that is squeezed between a horizontal crack between rock layers and hardens is called a sill. Dikes and sills can run from only a few meters to hundreds of meters long. Some magma that forms a sill can continue to push the rock layers upward. This forms a dome of rock called a laccolith.
CALDERA
When an eruption occurs, sometimes the top of a volcano can collapse down into the partially emptied magma chamber. This makes a humongous opening called a caldera.
PACIFIC RING OF FIRE
The Pacific Ring of Fire stretches from New Zealand, along the eastern edge of Asia, north across the Aleutian Islands of Alaska, and south along the coast of North and South America. It is over 75% of the world's active and dormant volcanoes.
HOW DO VOLCANOES RELATE TO PLATE TECTONICS AND EARTHQUAKES
Volcanoes relate to earthquakes in many ways. Plates move around always. When they move around long enough, they break and let energy out. With this energy comes magma. When magma comes out through the vent, it causes and eruption. An earthquake is caused when the energy goes through a fault line and quakes.
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