Volcanoes in Action

Violent and devastating, legendary in history andvolcanoes are also called Strato volcanoes and
mythology, volcanoes in action are among theachieve the well known high peaked form,
most powerful forces of nature. They havesometimes snow covered, like the often pictured
shaped the Earth for billions of years and continue12,400 feet high Mount Fuji, one of Japan's holy
to do so, sometimes with deadly consequencesmountains. Other well-known composite volcanoes
to life and property.are Vesuvius and Stromboli. There are several
Awesome to witness, erupting volcanoes arevariations of the composite shape.
natural geologic structures providing a conduit toShield Volcanoes are formed by lava that flows
the Earth's surface for the extrusion of molteneasily and without the potential violence of some
rock materials migrating upwards from the depthsof the other forms. They are much flatter with
beneath the Earth's crust. Volcanoes can occur onbroad summit areas and gently sloping sides. Many
land or on the seabed beneath the oceans.of the largest volcanoes on Earth are shield
Molten rock, or magma, to use its propervolcanoes.
geological name for a body of molten rock foundProbably the best example is the Hawaiian Islands,
at depth, exists under pressure deep within theall of which are shield volcanoes and the tallest of
Earth. When overlaying solid rocks provide athese, measured from its base on the ocean
channel, perhaps because of the constantlyfloor, is Mauna Kea, higher at 30,000 feet than
occurring internal adjustments of the surroundingMount Everest. The Hawaiian Islands are not like
rocks, the magma may escape to move upwardthose of the Pacific Ring of Fire but are called
to regions of lower pressure until eventuallyplume volcanoes. The molten material that feeds
emerging at the surface, acquiring the new name:plume volcanoes originates from very deep in the
lava. On the other hand, magma that cannot findEarth's mantle, thought to be possibly from about
a outlet will become trapped at some sub-surface1900 miles below the surface, far deeper than the
location for ever.magma source for other types of volcanoes.
Magma and lava are similar but not the same.Lava Domes are formed from very thick lava
With the relief of pressure on the upward movingthat flows slowly with difficulty, cooling and
magma, much of the gaseous component is ablecrystallizing before traveling far from its exit vent
to escape, thus changing its composition. Thisand are often comprised of more than one flow,
modified molten rock will emerge at the surfaceforming lumpy chunks of hardened lava. Lava
and then be called lava. In some cases thedomes often occur in the craters or on the sides
volcanic lava reaches the end of its upwardof composite volcanoes.
journey with a volatile mixture of molten rock,Volcanic eruptions are most often remembered
gases, and water, expanding and exploding withfor the devastation they have caused and many
such force that molten lava, rock fragments anderuptions have become especially infamous.
ash are violently propelled into the air to greatAlmost everyone has heard of the Indonesian
heights.island of Krakatoa where in 1883 two thirds of
Active volcanoes release carbon dioxide and otherthe island vanished with an explosion estimated to
gasses into the atmosphere, including significantbe 10,000 times more powerful than the atomic
amounts of water vapor. Volcanoes are not rare,bomb explosion over Hiroshima at the end of
and with tens of thousands of volcanoes eruptingWorld War Two. This awesome Krakatoa event
over the hundreds of millions of years of thewas followed by a deadly tsunami.
planet's early existence, the water vapor releasedAnother, equally well known event, is the eruption
by volcanoes provided the source of much of thein Italy of Mount Vesuvius in 79 AD where the
Earth's original oceans and much of itspopulation of nearby Pompeii was overwhelmed
atmosphere.and buried almost instantly to be found and
Although the dramatic scenes of devastationexcavated centuries later, becoming an attraction
resulting from volcanic eruptions capture ourfor historians and ordinary visitors.
attention and imagination, volcanoes have alsoAlso in the Mediterranean, about 1600 BC, the
created many benefits for the young Earth.island of Santorini and its civilization, now revealed
Volcanoes have produced gases that escape toby extensive archaeological excavations, was
warm the atmosphere and these gasesalmost destroyed in the largest volcanic eruption
contribute to the protective filtering of the Sun'sin the last 10,000 years. It is believed to have
harmful radiation. Volcanoes provide fertilizer forkilled more than a million people and wiped out the
the soil - most of which was derived fromentire Minoan civilization on the island of Crete.
volcanic outpourings in the first place, they provideSantorini may also have been the inspiration for
liquid in the form of water and nutrients and aPlato's island of Atlantis.
habitat that helps make life possible. VolcanoesOther similarly devastating eruptions were:
have created and are still creating all of the seaTambora, Indonesia, in 1815, with the aftermath
floor of the Earth's oceans as a result of thecausing 92,000 deaths. The eruption of Mount
outpourings at the mid-ocean ridges, thosePelee in the Caribbean in 1902 destroyed the city
mountain chains that stretch around the globe,of St.Pierre and claimed the lives of all 29,000
rising from the seabed. Most of the surface rocksinhabitants except for one person who was a
and materials of the Earth's crust are of volcanicprisoner in an underground jail cell.
origin. It is estimated that there are thousands ofAnd in recorded history there have been dozens
active volcanoes and also many dormantof other volcanic events that tell a similar story of
volcanoes that may re-awaken in the future.devastation and loss of life.
There are also many extinct volcanoes.And of course, in the United States in 1980 in the
Volcanoes occur all over the Earth, but many areState of Washington, the beautiful composite
concentrated at the edges of continents, orMount St. Helen's lost about1200 feet of its
beneath the sea where they form underwatersummit height in a spectacular eruption that, with
volcanic mountain ranges, or long chains of islandsthe aid of television, was witnessed live by so
such as those of Hawaii. A large number of activemany of us.
volcanoes encircle the Pacific Ocean basin andAnd more recently in the United States, in Alaska,
have acquired the name "Pacific Ring of Fire".where there are many volcanoes, the Mount
There is a particular reason for this configurationRedoubt Volcano that had been under close
over thousands of miles and the explanation forobservation for many months, finally erupted on
this involves a well established geological theoryMarch 22nd of this year, 2009, with considerable
known as Plate Tectonics - but that is a little tooviolence that sent a massive cloud of volcanic ash
complex for discussion here. That same theoryto 50,000 feet into the stratosphere. No doubt
also explains the occurrence of volcanoes at thethere will be other such eruptions throughout the
edges of continents.world.
The shape and structure achieved by volcanoesSome volcanoes erupt explosively. One such,
depends on the composition of the erupting lavareferred to above, being that of Mount St. Helen,
and the amount of energy and force at theirwhen on May 18, 1980, one of the largest
creation, with the main categories being,eruptions in the recent history of North America
somewhat descriptively: cinder cones, compositeoccurred. While not always erupting with such
volcanoes, shield volcanoes, and lava domes.violence, volcanoes have played a major part in
Following is a brief description of these severalshaping the Earth's crust over the course of time.
types.Some extreme eruptions, given the name
An example of a Cinder Cone is the famous"super-volcanoes", have, at different prehistoric
Paricutin Volcano of Mexico that quite suddenly, intimes millions of years ago, created vast volumes
1943, started to grow out of a farmer's field withof volcanic rock over huge areas in such regions
explosive eruptions of molten lava into the air,as Yellowstone in the United States, Japan, the
forming cinders that fell back to Earth around theNorth Island of New Zealand, the deccan traps of
point of eruption. As this continued, a cone ofIndia and the traps of Siberia, among others. Such
cinders slowly took shape until reaching a heightstupendous volcanic events as those, are thought
of 1200 feet. Paricutin stayed active for nineto have been major contributing causes in several
years, emitting ash that covered the surroundingof the mass extinctions that have occurred
area for miles and destroyed a nearby town.throughout the Earth's four and a half billion year
Composite Volcanoes, as their name implies, arehistory, including the well known mass extinction
formed of a composite of alternating layers ofevent associated with the demise of the
hardened lava and rock fragments. Compositedinosaurs 65 million years ago.