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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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
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
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.
Pryoclastic lava- the gas in thick magma breaks the rock into little pieces. These rocks
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.
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
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
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
Most of these earthquakes occur near plate boundaries, because there is a huge
strain from the plates, creating fault zones. .
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
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
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.
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.
- 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.