volcano
... 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 ...