VOLCANO

A volcano is a rupture in the crust of a planetary-mass object, such as Earth, that allows hot lava, volcanic ash, and gases to escape from a magma chamber below the surface.

VENTS

Vents, of course, are the locations from which lava flows and pyroclastic material are erupted. Their forms and orientations can be used to determine many characteristics of the eruption with which they were associated. There are two main end members in a spectrum of pyroclastic vents in Hawai'i, spatter vents and cinder cones. Their differences are due mostly to the gas content of the magma that is erupted. Additionally, there are satellitic shields formed during eruptions without fountaining and tuff cones formed during phreatomagmatic.

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MAGMA CHAMBER

[if gte vml 1]><v:shapetype id="_x0000_t75" coordsize="21600,21600" o:spt="75" o:preferrelative="t" path="m@4@5l@4@11@9@11@9@5xe" filled="f" stroked="f"> <v:stroke joinstyle="miter"></v:stroke> <v:formulas> <v:f eqn="if lineDrawn pixelLineWidth 0"></v:f> <v:f eqn="sum @0 1 0"></v:f> <v:f eqn="sum 0 0 @1"></v:f> <v:f eqn="prod @2 1 2"></v:f> <v:f eqn="prod @3 21600 pixelWidth"></v:f> <v:f eqn="prod @3 21600 pixelHeight"></v:f> <v:f eqn="sum @0 0 1"></v:f> <v:f eqn="prod @6 1 2"></v:f> <v:f eqn="prod @7 21600 pixelWidth"></v:f> <v:f eqn="sum @8 21600 0"></v:f> <v:f eqn="prod @7 21600 pixelHeight"></v:f> <v:f eqn="sum @10 21600 0"></v:f> </v:formulas> <v:path o:extrusionok="f" gradientshapeok="t" o:connecttype="rect"></v:path> <o:lock v:ext="edit" aspectratio="t"></o:lock> </v:shapetype><v:shape id="Picture_x0020_1" o:spid="_x0000_i1025" type="#_x0000_t75" alt="Resulta ng larawan para sa magma chamber of a volcano" style='width:468pt; height:291.75pt;visibility:visible;mso-wrap-style:square'> <v:imagedata src="file:///C:\DOCUME~1\jaylord\LOCALS~1\Temp\msohtmlclip1\01\clip_image001.jpg" o:title="Resulta ng larawan para sa magma chamber of a volcano"></v:imagedata> </v:shape><![endif][if !vml][endif]A magma chamber is an area beneath the Earth’s surface where magma (molten rock) collects in a pool of molten rock. Magma forms in subduction zones where an oceanic plate is overridden by another crustal plate. The descending plate begins to melt and the molten rock collects in these underground chambers. The magma is hotter than the surrounding rocks and is under great pressure.

The melting plates continues to add molten rock to the chamber increasing the pressure until it breaks the solid rock apart. The hot liquid rock is lighter than the surrounding rock so the magma forces its way upward where it can erupt during a volcanic eruption.

THROAT

It is the he uppermost section of the main vent that is known as the volcano’s throat. It is the entrance of a volcano and here the lava and volcanic ash are ejected.

PYROCLASTIC FLOW

Pyroclastic flows are fluidized masses of rock fragments and gases that move rapidly in response to gravity. Pyroclastic flows can form in several different ways. They can form when an eruption column collapses, or as the result of gravitational collapse or explosion on a lava dome or lava flow

These flows are more dense than pyroclastic surges and can contain as much as 80 % unconsolidated material. The flow is fluidized because it contains water and gas from the eruption, water vapor from melted snow and ice, and air from the flow overriding air as it moves downslope.

CRATER

A volcanic crater is a roughly circular depression in the ground caused by volcanic activity. It is typically a bowl-shaped feature within which occurs a vent or vents. During volcanic eruptions, molten magma andvolcanucx gases rise from an underground magma chamber, through a tube-shaped conduit, until they reach the crater's vent, from where the gases escape into the atmosphere and the magma is erupted as lava. A volcanic crater can be of large dimensions, and sometimes of great depth. During certain types of explosive eruptions, a volcano's magma chamber may empty enough for an area above it to subside, forming a type of larger crater known as a caldera.

VOLCANIC BOMBS

A volcanic bomb is a mass of molten rock (tephra) larger than 64 m (2.5 inches) in diameter, formed when a volcano ejects viscousfragments of lava during an eruption. They cool into solid fragments before they reach the ground. Because volcanic bombs cool after they leave the volcano, they are extrusive igneous rocks. Volcanic bombs can be thrown many kilometres from an erupting vent, and often acquire aerodynamic shapes during their flight. Bombs can be extremely large; the 1935 eruption of Mount Asama in Japan expelled bombs measuring 5–6 m in diameter up to 600 m from the vent. Volcanic bombs are a significant volcanic hazard, and can cause severe injuries and death to people in an eruption zone. One such incident occurred at Galeras volcano in Colombia in 1993; six people near the summit were killed and several seriously injured by lava bombs when the volcano erupted unexpectedly.

Volcanic bombs are known to occasionally explode from internal gas pressure as they cool, but in most cases, most of the damage they cause is from impact, or subsequent fire damage. Bomb explosions are most often observed in "bread-crust" type bombs.

VOLCANIC ASHES

Volcanic ash consists of fragments of pulverized rock, minerals and volcanic glass, created during volcanic eruptions and measuring less than 2 mm (0.079 inches) in diameter. The term volcanic ash is also often loosely used to refer to all explosive eruption products (correctly referred to as tephra), including particles larger than 2mm. Volcanic ash is formed during explosive volcanic eruptions when dissolved gases in magma expand and escape violently into the atmosphere. The force of the escaping gas shatters the magma and propels it into the atmosphere where it solidifies into fragments of volcanic rock and glass. Ash is also produced when magma comes into contact with water during phreatomagmatic eruptions, causing the water to explosively flash to steam leading to shattering of magma. Once in the air, ash is transported by wind up to thousands of kilometers away.

LAVA

Lava is molten rock generated by geothermal energy and expelled through fractures in planetary crust or in an eruption, usually at temperatures from 700 to 1,200 °C (1,292 to 2,192 °F). The resulting structures after solidification and cooling are also sometimes described as lava. The molten rock is formed in the interior of some planets, including Earth, and some of their satellites, though such material located below the crust is referred to by other terms.

A lava flow is a moving outpouring of lava created during a non-explosive effusive eruption. When it has stopped moving, lava solidifies to form igneous rock. The term lava flow is commonly shortened to lava. Although lava can be up to 100,000 times more viscous than water, lava can flow great distances before cooling and solidifying because of its thixotropic andshear thinning properties.