Volcanoes: What are volcanoes? Volcanoes are an opening in the
planets surface where debris and gases erupt through the crust They
are found near tectonic plates that are diverging or converging.
Volcanoes are also found near hot spots.
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Volcanoes continued 3 Basic Types of Volcanoes Shield Volcano-
huge volcanoes that are made up of many layers of lava flows The
volcano itself is broadly shaped, with a gently sloping cone.. They
are produced by hot spots or along the mid ocean ridge because of
sea floor spreading. Ex. Mauna Loa, which is 5 miles high.
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Composite Volcano: 2 nd type of volcano Composite volcano is
also known as the strato-volcano This is the the type of volcano
people think of when they hear the word volcano It has steep sides,
that are very smooth. There is a single central vent There are
alternating layers of material caused by lava flows Ex. Costa Rica-
Poa, Arenal, and Irazu volcanoes
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Cinder Cones Cinder cone volcanoes are made up of magma called
scoria that fall around the vent after a medium eruption They are
the simplest volcano Cinders are melted volcanic rock that when
erupted, become tiny pieces.
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How Volcanoes form: When plates are formed- one plate goes
under another plate. This makes the earth heat up and melts the
rock. Can be formed when the plates separate from each other. These
volcanoes are found on the ocean floor. Can be formed on hot spots.
Hot spots are places that have intense heat located in the mantle.
This heat makes magma move to the surface. Scientists are not sure,
but they believe that these are the result of mantle plumes. Ex.
The Pacific Ring of Fire
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Why Do Volcanoes Erupt: The rocks inside the Earth become hot,
and the rock begins to melt. When it melts, it is less dense than
the surrounding rock. An object that is less dense will rise and so
magma rises to the surface. If the magma has water in it and has
gas, when the magma reaches the surface, the gasses and warm water
will expand, and cause a violent eruption.
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Types of Eruptions There are many different types of lava. Some
are fast, some are slow, some are fluid and some are more solid.
Example: Pahoehoe- thin lava that forms basalt. Hi lava is fast
moving and is characterized by a glassiness and a rope like lava.
It often becomes a solid when it cools. Sheet lava- occurs from
fissure systems. It is also made up of basalt. However,, sheet lava
discharges basalt over a huge area. Aa lava- is made up of mama
inside the volcano and it is emitted from the vent. After this lava
cools, the surface is not smooth but is very rough. Block Lavas-
similar to aa lava flows but is thicker and stronger. It is very
slow moving. When block lavas cool, they are a lot smoother than aa
lava.
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Eruptions continued Pryoclastic lava- the gas in thick magma
breaks the rock into little pieces. These rocks are callled
pyroclasts. Dike swarm- when magma that is a liquid comes from
dikes. Strambolian- molten lava erupts from the summit crater in
large clots. Vulcaninan- the volcano erupts a cloud of gas that is
full of ash. Vesuvian- this eruption forms a shape that is similar
to a cauliflower and is made up of smoke and gas. Pelean- gas,
dust, ash, and lava erupt from the crater. Phreatic- a steam
eruption caused when surface water and cold ground touch hot magma.
Plinian- one of the works eruptions. It is very explosive and very
dangerous.
Fun facts about Volcanoes -There are about 1,500 active
volcanoes in the world. -Indonesia has the most volcanoes -There
are about 40 active volcanoes in the lower part of the US. Alaska
also has - about 60. However, we do not know for sure because
sometimes there are eruptions -From something we have not
classified as a volcano. -There are also underwater volcanoes-
underwater volcanoes are very explosive. -The biggest volcano is
Mauna Loa in Hawaii. It is 13,000 feet above sea level. -The oldest
volcano is Etna. She is about 350,000 years old. -500 million
people live near active volcanoes.
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Worst volcanoes Santorini 1650- took place in Greece. People
can only guess about the death toll but this volcano destroyed
entire civilizations Tuba- April 10-15, 1816 in Indonesia- killed
about 92,000 people. Tuba was felt worldwide.1816 became a year
without a summer because the volcanic ash lowered worldwide
temperatures. It snowed in New England in June, and crop failures
were felt in Northern Europe and North America. -Mt. Krakatoa,
Indonesia August 26, 1883- destroyed 2/3 of the Island, emitting 6
cubic miles of debris into the atmosphere. This volcano was the
loudest volcano ever documented and about 36,000 people died.
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CONSEQUENCES People die Many people are forced to evacuate They
can change thee weather- cause rain, long term effects on the
climate Fast moving lava can kill people Ash can make it hard to
breathe Can indirectly cause famines, fires, and earthquakes Lava
can kill plants and animals - Mount St. Helen killed about 24,000
animals Acid rain Damages to forests and soil Flourine will poison
wildlife and contaminate water supplies Landslides Lahars or
mudflows- destroy houses, trees, and boulders
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Benefits Volcanoes do have some benefits Volcanic ash is very
good for soil so after a volcano, plants tend to grow very quickly.
Volcanic slopes are usually very steep so animals and plants can
live there and be protected. Lava preserves fossils.
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What are Earthquakes and why do they Rock Our World An
earthquake is a vibration that moves throughout the earths crust.
Plate tectonics- the surface layer of the earth ( the lithosphere)
has many plates that slide over the athenosphere layer. At the
boundaries between these huge plate, three things can occur: -
plates can move apart (divergent) - plates can come together
(Subduction/Convergent plates) - plates slide against each other-
transform boundaries. When these plates meet, they create faults
*breaks in the earths curst). This is where earthquakes happen. The
break that creates a fault along with the shifts that occur along
faults cause the earthquakes. Most of these earthquakes occur near
plate boundaries, because there is a huge strain from the plates,
creating fault zones..
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Earthquakes continued
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More pictures
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Seismic waves When there is a break or shift in the earths
crust, energy becomes seismic waves. Types of waves: - Body waves-
move through the inner part of the wave - surface waves- travel
over the surface of the earth surface waves- L waves are the most
damaging waves, because they create the biggest vibrations. 2 types
of Body waves: - P waves (primary or compressional waves) travel
1-5 miles per second. They are very fast and can travel through a
solid, liquid or gas. - S waves (secondary)- are slower than p
waves. They move rock particles outward, pushing them perpendicular
to the waves. This is the first period of rolling. They do not move
through liquid or gas. These wave forms are what cause the up and
down and back and forth motions
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Measuring the strength Richter scale- measures the magnitude of
the earthquake Is based on maximum strength of vibrations and the
distance of the instrument the epicenter of the earthquake. It
shows how much energy is released. This data is found out using a
seismograph. Mecall Scale- measures the extent of damage
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Predicting earthquakes Scientists can predict where major
earthquakes might occur, based on what they know about the plates
and fault zones. They might also look at the history of the region
and from knowing where pressure is building However, predictions
are exactly that and are not always true Scientists do better
predicting aftershocks.
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Facts about Earthquakes The largest earthquake in the US was a
9.2 Magnitude that happened in Alaska, 1964. The larges earthquake
in the world was a 9.5 magnitude in Chile, 1960. Tsunamis can be a
cause of earthquakes. Hypocenter- location beneath the earths
surface where the rupture of the fault begins Epicenter- location
above the hypocenter on the surface of the earth. There are about
500,000 detectable earthquakes in the world 100,000 of these can be
felt, and 100 of these does damage The worlds deadliest earthquake-
1556, China. This killed 830,000 people. Alaska is the most
earthquake prone state.
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Nore examples of earthquakes - Sichuan province, China 2008,
87,000 people were killed or missing and 370000 were injured in
just one country from an earthquake. -Pakistan and Kashmir,
)October 2005- killed more than 73,000 people and left millions
homeless. - Nias, Indonesia- March 2005- 1,300 people killed -
Peruvian Andes- 1970- more than 66,000 people were killed because
the earthquake triggered a landslide and buried the town of Yungay.
- Kanto earthquake- 1923- 142,800 people in the Japanese capital
were killed.
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Consequences Thousands of people can die Landslides
Liquefaction- Tsunamis Buildings are destroyed, as well as houses
Floods Injuries Houses, buildings, railroads, highways, tunnels,
bridges, water, gas and sever lines can all be destroyed.
