EARTHQUAKES

Earthquakes: Movement of the Earth’s Crust

Earthquakes are the shaking and moving of the ground when energy is released in waves. These waves are called seismic waves. These waves are similar to ocean waves, which move through water. Seismic waves, however, move through the ground.

Most earthquakes are caused by the movement of large sections of the Earth’s crust, called plates. The place where two plates meet is called a fault. Faults look like large cracks in the ground. If the two plates move in different directions, they build up energy at the fault line. When enough energy builds up, the stress on the fault becomes too great and it ruptures. This releases the energy and the ground starts to shake.

Earthquakes can also be caused by other natural events, such as landslides and volcanoes. Man-made earthquakes happen because of nuclear testing and mining explosions.

The first movement of an earthquake, called the main shock, is often followed by smaller ground trembles, called aftershocks. These aftershocks are the plates settling into their new position. Aftershocks can continue for days after the main shock.

There are an estimated 500,000 earthquakes around the world each year. Most are so mild they are only recorded on scientific instruments. Only about 100,000 can be felt by humans. Of these, only about 19 a year cause major damage. Major earthquakes in populated areas can cause huge destruction. Buildings collapse, roads and bridges buckle and crack, and electrical and gas lines break and cause fires. If the earthquake happens in the ocean, it makes a series of huge ocean waves called a tsunami. The tsunami travels until it finally reaches land, where it causes large flooding.

Scientists are searching for ways to predict earthquakes. They study the historical patterns of earthquakes and monitor the movement of the plates with seismic equipment. While they cannot predict an exact date of a future future earthquake, they have a better understanding of when earthquakes are more likely to happen.

Here you have two nice videos to illustrate how the earth crust moves:

Volcanos and  plates movement:      https://youtu.be/Kg_UBLFUpYQ

Earthqueakes:   https://youtu.be/-zNyVPsj8zc

REALLY INTERESTING WEBSITE ABOUT EARTH CRUST MOVEMENTS IN GENERAL

http://info.geonet.org.nz/display/appdata/Applications+and+Data

Volcanoes

When a volcano erupts hot gases and liquid rock come up to the surface from inside the earth. The material sometimes slides down mountains as lava or is hurled into the air as ash or small rocks. Volcanoes often destroy the land around them completely. Gases from eruptions can keep sunlight from reaching the earth and darken the sky for years. Volcanoes also build up new islands and mountains and make the soil a good place for crops to grow.

Where are volcanoes located?

The earth’s crust is made up of sections or plates. They always move and at places where they get together they collide or slide on top of each other.

90% of all volcanoes are located around the edges of the Pacific Ocean. The Pacific coasts of Asia, North America and South America form a big circle, which is called the Ring of Fire.

Sometimes volcanoes are found in places where plates move away from each other. In the Atlantic Ocean, for example, a long range of underwater mountains forms the border between two plates. Iceland is a gigantic volcanic island that has come up to the surface from this mountain range.

Other volcanoes form in the centre of plates, where magma comes up from deep inside the earth and breaks through the crust. Such areas, like the Hawaiian Islands , are called hot spots.

         






How volcanoes are formed

Hot liquid rock, called magma, makes up the inner part of the earth. When it rises to the surface it cools down and sometimes the flow of magma stops in the inner part. In other places, magma unites with gas and creates chambers below the surface of the earth. When the gas pressure gets higher, magma becomes lighter and it spews out of openings, cracks or vents at the surface.

Volcanic eruptions

When a volcano erupts three types of material come to the surface: lava, small pieces of rock or ash, and gas.

Magma that spreads out of a volcano slowly is called lava. It can reach temperatures of up to 1,200° C and glows red to white when it flows. In most cases, lava mixes with steam and gas. All types of lava contain silicon and oxygen. As lava moves down a volcano’s slope it cools down and becomes harder, creating very rough blocks or rock.

Small pieces of rock erupt from a volcano when magma is trapped inside and cannot get out. Gas pressure in the magma chambers gets high and suddenly material is blown out and thrown high into the sky.

Often, the pieces of rock are so tiny that they form ash or dust. Strong winds can blow volcanic dust hundreds or thousands of kilometers away from the place of eruption.

Types of volcanoes

The two most common types of volcanoes are stratovolcanoes and shield volcanoes.

Stratovolcanoes are formed like a cone. The base is rather flat and they become steeper towards the peak. A crater usually forms at the top of the volcano. Such volcanoes develop when lava and ash come up from the inner part of the earth and build up layers. First, lava spreads over the surface of the volcano , cools down and becomes hard. Then pressure builds up underneath the layers of lava and ash and other materials are blown out. One of the most famous stratovolcanoes is Mount Fuji in Japan.

Shield volcanoes are dome shaped mountains which are flatter than stratovolcanoes and built of lava flows. They may start on the sea floor and become so large that islands can rise far above sea level. The Hawaiian mountains were formed this way. The islands, which rise about 10,000 meters above the ocean floor, are the world’s most massive volcanoes .

Volcanoes also create holes, called craters and calderas. Calderas are larger than craters and are formed when parts of the volcano collapse. Sometimes these holes are filled with water and form a lake.

Volcanic activity

Some volcanoes are active. They erupt very often, like Italy’s Mount Etna, which erupts every few years. Inactive volcanoes have not erupted for a long time, but scientists warn that they may become active some day. Extinct volcanoes, like Mount Kenya in Africa, will probably never erupt any more.

Volcano experts do their best to warn the population when a volcano may erupt. Sometimes smaller earthquakes or clouds of gas from vents tell observers that a volcano could erupt soon. Most of the time, however, there are no signs at all.

Effects and benefits of volcanoes

Although volcanoes may cause a lot of damage and big eruptions can kill many people, there are also advantages of volcanic activity.

Volcanic lava and ash spreads over the slopes of mountains and creates good farmland. Volcanic rock is used to build roads, make special tools and ornaments.

The heat that is formed underneath a volcano is called geothermal energy. Hot water that lies below the surface is used to heat homes and greenhouses. Countries with many volcanoes like Japan, Iceland or Italy use this kind of energy to produce electric power.

VOCABULARY

blow out = explode , erupt

border = the line that separates two objects

chamber = a closed space or room

collapse = to fall down very quickly

collide = to crash

cone = a shape that is round at one end and pointed at the other

covers = has an area of

crack = a very small or narrow opening in an object

crater = a round hole in the ground formed by an explosion

create = make

crops = a plant like wheat or rice that farmers grow and use as food

crust = the hard outer layer of the Earth

cylinder cone =shape that is round on one side and pointed at the end

develop = grow

dome-shaped = formed like the round roof of a building

drowned = to be killed by water

dust = a powder that has very small bits of dirt

earthquake = when the Earth's surface suddenly shakes and creates a lot of damage

edge = border

erupt = to explode and send smoke, rock and fire into the sky

eruption = when a volcano explodes

extinct = something that does not exist any more

flow = the slow movement

gigantic = very, very big

hurl = throw

hurl = throw

lava = hot liquid rock that flows from a volcano

layer =cover

liquid =fluid, like water

located = are found

magma = the melted rock that is below the surface of the Earth

massive = very, very big

mountain range = a group of mountains that form one line

mudflow =when it rains and the earth gets very soft and full of water the sides of hills can move down and destroy roads or houses

oxygen = a gas that is in the air and that we need to breathe

plate = one of the many sheets of rock that form the surface of the Earth

pressure =force, weight

release = to set free

Ring of Fire = the land around the Pacific Ocean where plates get together— many volcanoes can be found here

rise = to come up

rough blocks = hard blocks with an uneven surface

scientist =a person who is trained in science

sea level =the normal height of the sea; it is used for measuring other heights , like the height of a mountain

shield =here: the form of the volcano that is very flat

sign = a signal that says that something will happen

slide = to move smoothly over something

slope =mountain side

soil =earth, dirt

spew = to flow out very quickly

spread = to move out of

steam = the gas that water produces when you make it very hot

steep =sharp, not flat

vent = a round hole through which gases, magma or lava can get to the surface