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Volcanoes and Earthquakes NATURAL DISASTERS. Volcanoes: What are volcanoes?. Volcanoes are an opening in the planet’s 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 what are volcanoes
Volcanoes:What are volcanoes?
  • Volcanoes are an opening in the planet’s 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.
volcanoes continued 3 basic types of volcanoes
Volcanoes continued3 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 ½ miles high.
composite volcano 2 nd type of volcano
Composite Volcano: 2nd 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

cinder cones
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.
how volcanoes form
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

why do volcanoes erupt
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.

types of eruptions
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.
eruptions continued
Eruptions continued

Pryoclastic lava- the gas in thick magma breaks the rock into little pieces. These rocks

are callledpyroclasts.

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


Plinian- one of the works eruptions. It is very explosive and very dangerous.

gases that volcanoes emit
Gases that volcanoes emit
  • Water
  • Carbon dioxide
  • Sulfar dioxide
  • Hydrogen chloride
  • Hydrogen flouride
fun facts about volcanoes
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.
worst volcanoes
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.

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


Lahars or mudflows- destroy houses, trees, and boulders


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


what are earthquakes and why do they rock our world
What are Earthquakesand why do they Rock Our World

An earthquake is a vibration that moves throughout the earth’s 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 earth’s 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. .

seismic waves
Seismic waves

When there is a break or shift in the earth’s 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

measuring the strength
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

predicting earthquakes
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.

facts about earthquakes
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 earth’s 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 world’s deadliest earthquake- 1556, China. This killed 830,000 people.

Alaska is the most earthquake prone state.

nore examples of earthquakes
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


- 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.


Thousands of people can die




Buildings are destroyed, as well as houses



Houses, buildings, railroads, highways, tunnels,

bridges, water, gas and sever lines can all be destroyed.