Volcanoes
What is a volcano?
A volcano is a mountain that opens downward to a pool of molten rock below the
surface of the earth. When pressure builds up, eruptions occur. Gases and rock
shoot up through the opening and spill over or fill the air with lava fragments.
Eruptions can cause lateral blasts, lava flows, hot ash flows, mudslides,
avalanches, falling ash and floods. Volcano eruptions have been known to knock
down entire forests. An erupting volcano can trigger tsunamis, flash floods,
earthquakes, mudflows and rockfalls.
How are volcanoes formed?
Volcanoes are formed when magma from within the Earth's upper mantle works
its way to the surface. At the surface, it erupts to form lava flows and ash
deposits. Over time as the volcano continues to erupt, it will get bigger and
bigger.
What are the different stages of volcanoes?
Scientists have categorized volcanoes into three main categories: active,
dormant, and extinct. An active volcano is one that has recently erupted and
there is a possibility that it may erupt soon. A dormant volcano is one that has
not erupted in a long time but there is a possibility it can erupt in the future. An
extinct volcano is one that has erupted thousands of years ago and there’s no
possibility of eruption.
Why do volcanoes erupt?
The Earth's crust is made up of huge slabs called plates, which fit together like a
jigsaw puzzle. These plates sometimes move. The friction causes earthquakes
and volcanic eruptions near the edges of the plates. The theory that explains this
process is called plate tectonics.
What are plate tectonics?
The theory of plate tectonics is a interesting story of continents drifting from
place to place breaking apart, colliding, and grinding against each other. The
plate tectonic theory is supported by a wide range of evidence that considers the
earth's crust and upper mantle to be composed of several large, thin, relatively
rigid plates that move relative to one another. The plates are all moving in
different directions and at different speeds. Sometimes the plates crash together,
pull apart or sideswipe each other. When this happens, it commonly results in
earthquakes.
How many volcanoes are there?
There are more than 1500 active volcanoes on the Earth. We currently know of
80 or more that are under the oceans. Active volcanoes in the U.S. are found
mainly in Hawaii, Alaska, California, Oregon and Washington.
What are the different types of volcanoes?
Volcanoes are grouped into four types: cinder cones, composite volcanoes, shield
volcanoes and lava volcanoes.
Cinder cones are circular or oval cones made up of small
Cinder
fragments of lava from a single vent that have been
Cones
blown into the air, cooled and fallen around the vent.
Composite volcanoes are steep-sided volcanoes composed of many
layers of volcanic rocks, usually made from high-viscosity lava, ash
Composite
and rock debris. Mt. Rainier and Mount St. Helens are examples of
Volcanoes
this type of volcano.
Shield volcanoes are volcanoes shaped like a bowl or shield in the
middle with long gentle slopes made by basaltic lava flows. Basalt
Shield
lava flows from these volcanoes are called flood basalts. The
Volcanoes volcanoes that formed the basalt of the Columbia Plateau were
shield volcanoes.
Lava domes are formed when erupting lava is too thick to flow and
makes a steep-sided mound as the lava piles up near the volcanic
Lava
vent. The eruption of Mount St. Helens in 1980 was caused in part
Volcanoes
by a lava dome shifting to allow explosive gas and steam to escape
from inside the mountain.
What is the difference between lava and magma?
Magma is liquid rock inside a volcano. Lava is liquid rock (magma) that flows out
of a volcano. Fresh lava glows red hot to white hot as it flows.
Why does lava take a long time to cool down?
Lava cools slowly because lava is a poor conductor of heat. Lava flows slow down
and thicken as they harden.
What is a pyroclastic flow?
A pyroclastic flow is a fluidized mixture of solid to semi-solid fragments and hot,
expanding gases that flows down the sides of a volcano. These awesome features
are heavier-than-air emulsions that move much like a snow avalanche, except
that they are fiercely hot, contain toxic gases, and move at phenomenal,
hurricane-force speeds. They are the most deadly of all volcanic phenomena.
What is lahar?
A lahar is a type of mudflow or debris flow composed of pyroclastic material,
rocky debris, and water. The material flows down from a volcano, typically along
a river valley. It is very dangerous because it's consistency and the way it acts is
very much like cement. It is liquid when it's moving, but when it stops, it
solidifies. This can cause just as much devastation as lava itself.
What is pumice?
Pumice is a light, porous volcanic rock that forms during explosive eruptions. It
resembles a sponge because it consists of a network of gas bubbles frozen amidst
fragile volcanic glass and minerals. All types of magma (basalt, andesite, dacite,
and rhyolite) will form pumice.
What is the largest active volcano?
The world's largest, active volcano is Mauna Loa in Hawaii, where famous coffee
is grown in the rich volcanic soils. Mauna Loa is 13,677 feet above sea level. From
its base below sea level to its summit, Mauna Loa is taller than Mount Everest.
What is the Ring of Fire?
The Pacific Ring of Fire is an area of frequent earthquakes and volcanic eruptions
encircling the basin of the Pacific Ocean. The Ring of Fire has 452 volcanoes and
is home to over 50% of the world's active and dormant volcanoes. Ninety percent
of the world's earthquakes and 81% of the world's largest earthquakes occur
along the Ring of Fire.