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GEOGRAPHY

FALL SEMESTER of 2020

INSTRUCTOR: Oljeta Proga

oproga2019@loretomullingar.com

24 JUNE 2020

INSIDE THE EARTH

The earth was formed about 4.5 billion years ago. At first, it was a giant ball of molten melted rock. As the Earth cooled, three different layers formed.

The outside layer of Earth is called the crust. It is made up of solid rock. The crust is up to 60 kilometres thick under the Continents and 10 kilometres thick under the oceans. It floats on the magma in the mantle.

Surrounding the core is the mantle. The mantle is also very hot, about 4000 degrees Celsius. It is made up of molten and semi-molten rock called magma.

At the centre of the Earth is the core made up of nickel and iron. The temperature there is 5000 degrees Celsius. It is divided into 2 parts: The inner core and the outer core. The inner core is a solid ball due to pressure. The outer core is molten.

MOVING PLATES

The crust of the Earth is like a huge jigsaw puzzle and is broken into pieces called plates. There are two types of plates: Oceanic plates which occur under the ocean and continental plates which occur under the continents. The edges of the plates are called plate boundaries. Plate boundaries are where they separate by faults are cracks in the crust. Convection currents in the mantle cause the plates to move.

CONVECTION CURRENTS

Convection currents are large currents of hot magma that circulate in the mantle. Convection currents in the mantle move the Earth's plates.

The heat of the Earth's core causes magma to heat up, become lighter and rise.

When the hot magma reaches the underneath of the crust, it spreads out in all directions, dragging the crust with it.

The magma then cools slightly, as it is further from the core. This makes it heavier.

The heavier magma sinks back down towards the core where it is heated again.

This cycle is repeated again and again in a circular motion causing convection currents.

HOW VOLCANOES ARE FORMED

A volcano mountain or volcano forms when magma said to the surface of the Earth through a small opening called a vent.

The magma is stored underground in a magma chamber. The gases build-up in the magma chamber. The pressure from the gases causes the magma to erupt out of the vent through an opening called a crater.

When magma reaches the Earth's surface it is known as lava. The lava flow cools down and hardens around the vent.

Other materials such as ash also ejected from a volcano when it erupts.

After repeated eruptions, layers of ash and lava build up around the vent to form a cone-shaped mountain.

THE LIFE CYCLE OF A VOLCANO

Volcanoes go through different stages. They start as active volcanoes. Over time they may become dormant and eventually, all volcanoes become extinct.

stage

description

example

active

Erupts regularly

Mount Etna in Italy

dormant

Has not erupted for some time.

Mt. st. Helen

In America

extinct

Has not erupted in historic time

Slemish in Antrim

DESTRUCTIVE PLATE BOUNDARIES

Where plates Collide volcanoes form. The heavier crustal plate sinks below the lighter crustal plate. As it melts a blob of magma breaks off and moves up through the crust. Overtime this magma can erupt and form a volcano.

CONSTRUCTIVE PLATE BOUNDARIES

Where plates separate volcanoes form. As the plates separate magma rises up through the crust. The magma cools very quickly and builds up over time.

MID OCEAN RIDGES

A mid-ocean ridge is a mountain range that forms under the ocean as a result of volcanic activity.

A mid-ocean ridge formed when two plates pull apart causing a fissure in the Earth's crust.

Magma travels up through the figure onto the Ocean Floor. When it meets the cold seawater cause rapidly and solidifies.

Over time following a series of eruptions the ocean floor is built up to form a ridge of volcanic mountains.

E.g. the Mid-Atlantic Ridge

THE PACIFIC RING OF FIRE

The Pacific Ring of Fire is a zone of active volcanoes and earthquakes running around the edge of the Pacific Ocean. the volcanoes mark out the edge of the Pacific plate, and the volcanoes are the most active in the world.

HOW AND WHY EARTHQUAKES OCCUR

An earthquake is a sudden shaking of the Earth's crust. Earthquakes are caused by two plates slipping past each other.

Fault lines are long deep cracks in the crust and separate different plates. As the plates move, they sometimes get stuck. Energy builds up and becomes too great over time. The plates slip suddenly and violently past each other.

The point where the earthquake begins underground is called the focus.

When this happens, shockwaves or tremor's move through the earth-shaking rocks as they go. This is an earthquake.

The epicentre is the point on the Earth's surface directly above the focus.

Tremors spread outwards from the epicentre. After there is an aftershock that follows the main earthquake. These can sometimes cause more damage than the initial earthquake.

DISTRIBUTION OF EARTHQUAKES

Earthquakes occur at all three types of plate boundaries: constructive, destructive and conservative. One of the most famous fault lines in the world is San Andreas fault, California, USA. It is the boundary between the Pacific and American plates and runs for a 1300 km.

HOW WE MEASURE EARTHQUAKE ACTIVITY

A seismograph is an instrument used to measure and record earthquakes. The Richter Scale registers the strength or magnitude of an earthquake. This scale ranges from 1 to 10 and an increase of one unit on the scale means that an earthquake is 10 times more powerful. The higher the number an earthquake measures on the Richter Scale, the greater the destruction it causes. The Richter Scale is the scientific measurement of an earthquake’s magnitude. The Mercalli scale is also used and is based on eye witness observations. It ranges from 1-12( 1= no damage, 12= total destruction). It measures the damage caused by earthquakes. It was developed by Giuseppe Mercalli in 1902.

TSUNAMI

If an earthquake occurs under the ocean it can produce a tsunami. A tsunami is a huge wave that is quickly towards the shore, causing major damage and loss of life. For example, the Japanese Tsunami of 2011 killed 16,000 people.

The sudden vertical movements of plates displace the seawater. Tsunamis happen in the shallow and are the earthquakes measuring 7 or more on the Richter Scale occur under the ocean.

The energy from the earthquake is transferred by waves through the sea.

They can rise to 30 m high.

The water floods the coastline, depending on the location.

THE FORMATION OF FOLD MOUNTAINS

Fold mountains are formed when two plates move towards each other and collide. This causes sediments and rocks to crumble. The force of the plates pushing together the cause the Land above to buckle forming fold mountains. An anticline is a long, narrow ridge formed by folding at a colliding plate boundary. This is why fossils are sometimes found high up in the mountains. A syncline is a name given to a downward fold. Synclines are the valleys lying between the mountains.

DISTRIBUTION OF FOLD MOUNTAINS

There are 3 main fold mountain periods on Earth: Alpine, Armorican and Caledonian.

The Caledonian fold mountains: these are mountains named after the Latin name for Scotland. They have formed 400 million years ago. They include mountains in Donegal, Wicklow and Scotland. The mountains have rounded peaks.

The Armorican fold mountains: In Ireland, they include the McGillicuddy’s Reeks, the Galtees, the Knockmealdowns and the Comeraghs. These have worn out over time. The Munster mountains were formed 250 million years ago.

The Alpine fold mountains: These were formed 30 to 35 million years ago. They are the youngest and highest mountains in the world. They include the Rockies in America, the Alps in Europe and the Himalayas in Asia.

CONTINENTAL DRIFTS

In 1912 a German scientist called Alfred Wenger wrote that 200 million years ago the plates of the crust were all part of one landmass called Pangea. Who wrote that the plates moved and by 65 million years ago they had reached their present-day location. He called the theory of plate movement continental Drift. Wenger could not explain how the plates moved. This theory was not accepted until 1963 when earth scientists discovered that convection currents in the mantle cause the plates to move. Plate tectonics is a theory that explains the movement of plates and continental drift.

WHAT HAPPENS AT PLATE BOUNDARIES?

Constructive

plate boundaries

Destructive plate boundaries

Passive plate boundaries

type

where

2 plates move away from each other

2 plates collide

2 plates move side by side

what

2 plates are pulled apart by convection currents

Convection currents cause to plates to collide. The heavier one sinks and the lighter one buckles upward.

2 plates move side by side. They can move in opposite directions or in the same direction but at a different speed. Sometimes they get stuck.

features

volcano

Fold mts.

Earthquakes

examples

Mid Atlantic Ridge

Andes mountains

San Andreas fault

The end