Deep inside the Earth between molten iron core and crust, there is a solid body of rock called the mantle. When rock from the mantle melts and moves through the crust and releases gases, volcanoes erupt. Extremely high temperature and pressure causes the rock to melt. This melted rock is called magma. Once the magma has reached the surface it is known as lava.
Most
volcanoes occur on plate boundaries. Plate boundaries are areas where Earth's
plates slit apart or meet. Plate boundaries that are coming together ar
known as Convergent boundaries. Boundaries that are splitting apart are
known as Divergent boundaries. Transform fault boundaries ar sliding against
each other going in opposite directions.
Volcanoes
can occur on convergent or divergent plate boundaries or over a hot spot.
A hot spot is where a spot in the mantle heats up the plate above it.
All
volcanoes consist of a pipe, a vent, a crater, and a cone. The vent is
the opening at the Earth's surface. The pipe is the passageway in the volcano
in which the magma rises through. The crater is bowl shaped
and
is at the top of the volcano where ash and lava are released. The cone
builds up as more ash and lava become solid around the volcano.
Specific Volcanoes
Mount St. Helens
Mount St. Helens is located in southwestern Washington. It is 2,549 meters
tall, but it was 9,677 feet before May 18, 1980. Mount St. Helens is a
stratovolcano. It has erupted 2-3 times in the past 200 years. It's present
thermal activity is strong
steaming.
Mount St. Helens is 40,000 years old. It has been dormant since 1857. THe
first documented observation of Mount St. Helens was by George Vancouver
on May 19, 1792. He named it on Oct. 20, 1792. It was named after Alleyne
Fitzherbert (1753-1839) whose title was Baron St. Helens.
Mount Vesuvius
Mount
Vesuvius is located near Naples, Italy. It is in a region where
the African plate meets the Eurasian plate. Its last major eruption was
in 1944. Mount Vesuvius is 4,200 feet tall. Mt. Vesuvius is famous for
its largest eruption that took place in 79 AD and destroyed Herculaneum
and
Pompeii.
Mt. Vesuvius is around 300,000 years old. It is a stratovolcano. In 5960
BC and 3580 BC Vesuvius had two eruptions that rate among the largest known
in Europe. The eruption os 79 AD was the first volcanic eruption to be
described in detail. Vesuvius has erupted about 36 times since 79 AD
Hazards of Volcanoes
There
are six major hazards
that come with a volcanic eruption. Lava flows are one, they are very dangerous
but they usually go slow enough so people can get out of the way. Another
is falling ash, when gases escape from a volcano violently magma brakes
into pieces and bursts out as ash. Some more hazards are mud and debris
flows, tsunamis, volcanic earthquakes, and the release of deadly gases.
Causes of volcanos
Inside
of the earth's mantle the temperature is high enough to melt rock. This
melted
rock is called magma. The magma becomes buoyant so it rises. As
it rises some of it collects into magma chambers. As the magma gets close
to the earth's surface pressure decreases which causes the gases to expand.
This pushed the magma up through the earth's crust.
Signs That an Eruption is Likely
Most
volcanoes will provide typed of warnings
before an eruption. An explosive eruption could occur without warning but
there will most likely be signs for eruptions in the future. Steam blast
eruptions could occur. when the magma moves closer to the surface it will
most likely generate little earthquakes. It might also deform the ground
surface. Another warning is changes in the temperature and the chemistry
of ground and spring waters.
