My Science: Volcanoes

The Earth's Volcanoes

Most volcanoes are found at plate boundaries near the Pacific coast or at mid-ocean ridges. Here, fractures in the litosphere allow molten rock, called "magma", to rise from the mantle inside the Earth. Magma is known as "lava" when it flows out of a volcano. Ash, steam, and gas also spew out from a volcano and can cause a great deal of destruction.

In general, volcanoes, like earthquakes, occur near plate boundaries. Volcanoes are formed by plate destruction or the presence of a hot spot underneath the plate. Volcanoes are formed when magma from within the Earth's upper mantle works its way to the surface. At the surface, it erupts to form lava flows and ash deposits. Over time as the volcano continues to erupt, it will get bigger and bigger.

The Earth's crust is made up of huge slabs called plates, which fit together like a jigsaw puzzle. These plates sometimes move. The friction causes earthquakes and volcanic eruptions near the edges of the plates. The theory that explains this process is called plate tectonics.

Plate Tectonic

The theory of plate tectonics is a interesting story of continents drifting from place to place breaking apart, colliding, and grinding against each other. The plate tectonic theory is supported by a wide range of evidence that considers the earth's crust and upper mantle to be composed of several large, thin, relatively rigid plates that move relative to one another. The plates are all moving in different directions and at different speeds. Sometimes the plates crash together, pull apart or sideswipe each other. When this happens, it commonly results in earthquakes.

There are more than 1500 active volcanoes on the Earth. We currently know of 80 or more which are under the oceans.

Type of Volcanoes

Volcanoes are grouped into four types: cinder cones, composite volcanoes, shield volcanoes and lava volcanoes.

Cinder Cones	Cinder cones are circular or oval cones made up of small fragments of lava from a single vent that have been blown into the air, cooled and fallen around the vent.
Composite Volcanoes	Composite volcanoes are steep-sided volcanoes composed of many layers of volcanic rocks, usually made from high-viscosity lava, ash and rock debris. Mt. Rainier and Mount St. Helens are examples of this type of volcano.
Shield Volcanoes	Shield volcanoes are volcanoes shaped like a bowl or shield in the middle with long gentle slopes made by basaltic lava flows. Basalt lava flows from these volcanoes are called flood basalts. The volcanoes that formed the basalt of the Columbia Plateau were shield volcanoes.
Lava Volcanoes	Lava domes are formed when erupting lava is too thick to flow and makes a steep-sided mound as the lava piles up near the volcanic vent. The eruption of Mount St. Helens in 1980 was caused in part by a lava dome shifting to allow explosive gas and steam to escape from inside the mountain.

Sometimes volcanoes explode violently. Volcanoes that form from viscous lava are most likely to do this. Viscous lava tends to plug up volcanic vents. When pressure in the magma chamber increase, the lava is blown out. Pieces of rock and a great deal of ash are hurled high into the air. Clouds of ash and pumice flow like hot avalanches down the sides of the volcano. Mudflows (also called "lahars") are mixture of water and ash. They travel at great speed and engulf everything in their paths.

Product of explosive volcanoes:
1. Ash : Lava particles larger than dust cover the land

2. Lapili: Lava ejected in pea-sized pieces.

3. Pumice: Light-weight lava filled with holes

4. Bomb: Bomb-shaped lava forms as it flies in the air

5. Pele's hair: Sometimes drops of liquid lava blow into fine spiky strands. The threads form needles of volcanic glass. They are named Pele's hair after Pele, the Hawaiian goddess of volcanoes.

The Effect of Volcanoes Eruption to The Landscape of Environment

Movement in rocks underground can cause changes to the landscape above. The combination of heat and water in the Earth's rocks produce various phenomena. Molten rock erupting out of the Earth brings gases, mineral deposits, and water with it. Mud pools, hot springs, and geysers from when the gases and water escape. Mineral dissolved in the hot waters precipitate to form cone-like or terraced deposits of rocks.

The landscape around volcanoes:

1. Hot springs : Magma warms water in cracks in the rocks. Water returns to the surface as a hot spring. Occur where the water temperature is below the boiling point.

2. Mud pools: Steam, particles of rock, and vulcanic gases bubble through pools of liquid mud.

3. Fumaroles: Vents, or fumeroles, allow steam and other gases to escape from colling rocks.

4. Geysers: Heat from magma chambers causes ground water to boil, erupting as jets of steam and water. For geyser to occur there must be heat, water, and a plumbing system. A magma chamber provides the heat, which radiates into surrounding rock. Water from rain and snow works its way underground through fractures in the rock.

As the water reaches hot rock it begins to rise back to the surface, passing through rhyolite, which is former volcanis ash or lava rich in silica. The hot water dissolves the silica and carries it upward to line rock crack. This forms a constriction that holds in the mountain pressure, creating a geyser's plumbing system.