Volcanos Volcanos occur all over the world.The best know volcano zones occur on the destructive plate margin around the Pacific Ring of Fire.This chain of volcanos that lie along the west coast of central and south America,Japan and the Philippines,across New Zealand and into the Atlantic.Volcanos also occur in mid-ocean along the line of ocean ridges.The Mid-Atlantic Ridge is an example of ocean floor volcanos.When these volcanos erupt lava flows from the cracks building up the ocean floor.Volcanos can also occur away from plate boundaries.These are the Hawaiian Volcanos.As you can see there are lots of places were volcanos occur.Sometimes these volcanos are where humans have settled.To help protect our belongings and save human lives we have developed ways to predict when volcanos are about to erupt.Here are some. Predictions Two main methods are used to predict when volcanos are about to erupt.These methods are called geophysical techniques,and chemical techniques. The geophysical method can detect any changes in the rock below.As the magma rises it forces the rocks apart,Which can create minor earthquakes on and or around the mountain.These can be detected on a seismographs.A seismograph picks up the seismic waves the earthquake gives off and records them.A seismograph works by a pen and a weight suspended on a spring.As the earth shakes the pen writes the waves,called a seismogram,on a revolving drum.A comparison can be used.They take two or more seismographs readings to pin point exactly where the magma is trying to surface.This technique is successful in Hawaii where they are a lot of volcanos.The place and the time of eruptions have been forecast accurately.Before a volcano is about to explode the ground around it swells with magma.This causes the ground to start to tilt.The tilt can be measured by an instrument called a tiltmeter.Two containers are half filled with water.And a tube connects the two.As magma rises and changes the a! ngle of the earth.Water goes into the lower container.Scientist can tell if the volcano is getting more active.When magma moves its gravity changes.This change in gravity can be detected by using gravimeters.When rock is heated to a certain temperature.It looses its magnetism.And this can be detected with a magnetometer.When magma rises to the surface it gives off heat.This heat can be detected with a intfa-red temperature surveys.Sometimes chemical methods are used.They measure the volcanic gases at hit springs and at fumaroles which are openings in the ground were gases escape from.Just before a volcano is about to erupt there is an increase in certain gases.These gases are chlorine compounds,sulphor oxides,carbon dioxide,hydrogen, and radon. Damages When a volcano erupts huge amounts of lava are spewed out of the volcano.These huge flows of lava can wipe out towns.This type of volcanic eruption is called Hawaiian.These volcanos put on fire shows .They are rarely violent or explosive ,because the lava is fluid enough to let the gases escape easily.The lava flows out of boccas.These volcanos are not really dangerous.But they can cause alot of damage if people or buildings get in its way.A strombolian eruptions are more violent producing a lot thicker lava.Because the lava is thicker the gas can not escape easily from it making the lava hostile.The plinain eruptions ar the most dangerous .They hurl huge amounts of pumice as high as fifty kilometers into the atmosphere.Then is ash falls over wide areas.Then this is followed by pyoclastic flows,where hot gases and ash pour out of the vent.These flows rush across the landscape ,burning and burying anything in its path.This is the eruption that happened to Mount St. Helen in th! e U.S.A.
Wisps of steam were coming out of the vents on the side of the mountain.During a period of several weeks a three hundred foot high wedge shaped bulge developed on the south side of the mountain as a result of rock and ice being pushed up.There were gaping cracks in the glaciers.They were gray with a dusting in volcanic ash.Weeks later the bulge blew sending ash and mud slides down the mountain wiping any thing that got in its way.The eruption cause a lot of damage.It created the worlds biggest clear cut.Two hundred and thirty square miles of trees lay in a tangled mess after the eruption.But people were trying to save as much of the lumber as they could.They were hauling out Five hundred loads a day of the fallen trees.But of all those able to be salvaged one point eight billion board feet of timber was destroyed.The eruption also took out some human life.Sixty five people were killed in the eruption.But the most damage was done to the surrounding wildlife.Five thou! sand white tailed deer were killed,One thousand five hundred elk,two hundred black bears,fifteen mountains goats,plus unknown numbers of mountain lions,bobcats,small rodents,birds,fish,and insects were also killed.The whole population of spotted owls were completely wiped out.That was some things that can happen here are some more.Ash can bury structures and cause people to suffocate or if ash mixes with water it creates huge mud flows that race down mountain sides,clogging rivers.Hot chucks of lava and ash can start fires far from the lava flows.The earthquakes that accompany the eruptions can destroy buildings.The value of the damage consists of how bad the eruption was and if it was near any civilization.A very bad eruption near a city can cause millions and millions of dollars of damage and a great loss of lives. Even a small eruption with a lot of lava flow can cause millions of dollars of damage.If a volcano out in the wilderness explodes .The value of the damage can dif! fer.From how much value you place on the wildlife and trees.When Mount St. Helen exploded ash from the volcano clogged major rivers.The rivers were the Toutle and Cowlitz.The U.S Army Corps of Engineers took the task to unclog it.The cost of this was a quarter of a billion dollar.This gives you an idea how much money it costs to fix something damaged by a volcano. Precautions Because we sometimes have to live near volcanos.We have to take some precautions in case they ever erupt.All new buildings being built in the vicinity of volcanos should be earthquake proof .Mud flows,landslides,and lava can cause a lot of damage.There for dams and public buildings should be located so they don’t get destroyed by these forces.People should be aware of the warning signs of a volcano ,earthquakes and ash being spewed out.They should what to do if they have to leave the town quickly in case the volcano does blow. Reference sorces-The World Book Encyclopedia 18 pg223 We watched Mount St. Helen blow its top pg54-55,Mount St.
Helen 721-727,Volcanos and Earthquakes pg23-43,Science Dimensions pg236-237.