The theory of - #DLSGEO · VOLCANOES A volcano is an opening in the earth's crust through which...
81
Transcript of The theory of - #DLSGEO · VOLCANOES A volcano is an opening in the earth's crust through which...
The theory of PLATE TECTONICS
The topic of plate tectonics is largely based on Alfred Wegner's theory of
continental drift. Wegner was a German geophysicist and meteorologist who in
1912 hypothesized that the world's continents were moving. However, because
he could not prove his theory, it was not accepted until the 1950's. Wegener’s
evidence for continental drift was that:
the same types of fossilised animals and plants are found in South America and Africa.
the shape of the east coast of South America fits the west coast of Africa, like pieces in a jigsaw puzzle.
matching rock formations and mountain chains are found in South America and Africa.
Continental drift
225 million years ago all the continents were
joined together in one supercontinent called
Pangaea. Over millions of years, convection
currents started moving the continents apart
until there were two continents; Laurasia and
Gondwanaland.
Today the continents have moved even further
apart, creating the land masses that we know
today. The continents have not stopped
moving so in the future the world will look
different again.
the CROSS-SECTION of the Earth
Earth’s layers PROPERTIES
The Earth is made up of four distinct layers:
The inner core is in the centre and is the hottest part of the Earth. It is solid and made up of iron and nickel with temperatures of up to 5,500°C. With its immense heat energy, the inner core is like the engine room of the Earth.
The outer core is the layer surrounding the inner core. It is a liquid layer, also made up of iron and nickel. It is still extremely hot, with temperatures similar to the inner core.
The mantle is the widest section of the Earth. It has a thickness of approximately 2,900 km. The mantle is made up of semi-molten rock called magma.
The crust is the outer layer of the earth. It is a thin layer between 0-60 km thick. The crust is the solid rock layer upon which we live.
Plate BOUNDARIES
The Earth's crust is broken up into
pieces called plates. Heat rising and
falling inside the mantle creates
convection currents. The
convection currents move the
plates.
The point where two plates meet is
called a plate boundary. Earthquakes and volcanoes are
most likely to occur either on or near
plate boundaries.
types of
PLATE
BOUNDARIES
CONSTRUCTIVEplate boundary
As the plates move apart magma
rises from the mantle to the surface,
it cools and solidifies to form a new
crust. Eventually the new rock
builds up to form a volcano.
Formations:
Ocean ridges (Mid-Atlantic Ridge)
Volcanic islands (Iceland)
Ex: North American and Eurasian
plates
the MID-ATLANTIC RIGDE
Living on the MID-ATLANTIC RIGDE
Living on the MID-ATLANTIC RIGDE
Living on the MID-ATLANTIC RIGDE
DESTRUCTIVEplate boundary
The plates move towards each other. The oceanic plate is denser than the continental plate so it is forced underneath the continental plate. This is also called the subduction zone. As the oceanic plate is forced below the continental plate it melts into magma and earthquakes are triggered. Magma then rises up through cracks as a volcano.
Formations :
Trenches
Fold mountains
Ex : Pacific and Eurasian plates
the MARIANA
TRENCH
COLLISIONplate boundary
As the plates push together, the
continental crust is squashed
together and forced upwards.
Formations :
Fold mountains (Himalayas,
Alps)
Ex. Indo-Australian and Eurasian
plates
FOLDING
CONSERVATIVEplate boundary
Two plates slide past each other
in the same or opposite
directions. Plates usually move
at different speeds.
Formations :
Faults
Ex : North American and Pacific
plates (San Andreas Fault)
the SAN ANDREAS FAULT
VOLCANOES
A volcano is an opening in the earth's crust through which magma, ash and gas erupt. Volcanoes
can be different shapes although they are commonly cone shaped mountains as seen in this
picture. These cone shaped volcanoes are made up of layers of ash and lava. Most volcanoes are
found at plate boundaries.
Mount Fuji in Japan. This famous volcano sits close to the point where three tectonic plates meet.
CRATER
SECONDARY CONE
ASH CLOUD
VOLCANIC BOMBS
ASH
LAVA FLOW
LAYERS OF ASH AND LAVA MAIN VENT
MAGMA CHAMBER
SECONDARY VENT
Types of
VOLCANOES
Geologists and professional
volcanologists usually classify
volcanoes into four different
types, based on their shape,
magnitude, structure, material, and type of
eruption.
Why live in a DANGER ZONE?
Volcanoes have a wide range of effects
on humans. These can be problematic or
beneficial. It is usually the destructive
nature of volcanoes which is more widely
documented. However, many people
rely on volcanoes for their everyday
survival. Today, many millions of people
live close to volcanoes for this very
reason.
The BENEFITS of volcanoes…
Mount St. Helens
Mount St Helens is located in the Cascade mountain
range in the state of Washington in the United States
and is famous for its devastating 1980 eruption.
Causes of eruption
How did it happen?
Effects of the eruption
Responses to disaster
Super volcanoes
A super volcano is a volcano on a massive scale. It is different from a volcano because:
it erupts at least 1,000 km³ of material (a large volcano erupts around 1 km³)
it forms a depression, called a caldera (a
volcano forms a cone shape)
a super volcano often has a ridge of higher
land around it
a super volcano erupts less frequently -
eruptions are hundreds of thousands of years apart
Hotspots
A geologic 'hot spot' is an area in the
middle of a plate where molten
magma breaks through the thin crust A
hot spot under the American plate is
why Yellowstone National Park has
geysers and other thermal features. If
the hot spot is under the seafloor (as it
is in Hawaii) it produces undersea
volcanoes. Some of these volcanoes
build up to the surface of the ocean
and become islands.
Earthquakes
An earthquake is caused by the
shaking and vibration of the Earth's
crust due to movement of the
Earth's plates (plate tectonics).
Earthquakes can happen along
any type of plate boundary.
Earthquakes occur when tension is
released from inside the crust.
Kobe, Japan
Kobe is located in the south east of
Japan, near a destructive plate margin. It
is a megacity and has one of the largest
container ports in the world.
The earthquake that hit Kobe during the
winter of 1995 measured a massive 7.2 on
the Richter scale . At this plate margin, the
Pacific plate is being pushed under the
Eurasian plate.
Tsunamis
A tsunami is a huge wave, usually caused by volcanic or
earthquake activity under the ocean, which can
eventually crash onto the shoreline.
When an earthquake, volcano or landslide happens on
the ocean floor, water is displaced. This water forms the
start of the tsunami.
It is hard to see that a tsunami is approaching. The most
obvious sign is the coastal water retreats just before the
waves reach the shore.
TSUNAMI INDIAN OCEAN 2004
TSUNAMI JAPAN 2011
Predict…
It's not possible to prevent earthquakes and volcanic eruptions. However, careful management of these hazards can minimise the damage that they cause. Prediction is the most important aspect of this, as this gives people time to evacuate the area and make preparations for the event.
Predict…
Many of the prediction
techniques used to monitor
earthquakes are not 100 per
cent reliable. Planning and
preparing for an earthquake
is therefore very important.
