Transcript Subduction Zones

World Geo 3202
Unit 1: Land Forms Water Forms
September 2011
Outcomes
 In this lesson you will:
 1.1.1 Explain how compressional forces are caused. (k)
 1.1.2 Explain how tensional forces are caused. (k)
 1.1.3 Relate selected plate movements to compressional
and tensional forces. (a)
Earth
 To begin this unit we will look
at the external and internal
sections of the earth
 The exterior consists of land &
oceans
 Topography: is a general term referring to the surface
features of the earth like, hills, mountains, valleys,
plains, plateaus and other relief features.
 Complete the map activity before we explore the
interior
Topography Review
 Imagine you flew from the west coast of South
America to the east coast and you flew right along the
equator. What land forms would you fly over?
Earth’s Interior
 The earth's interior is neither all solid nor is it all
molten.
 There are layers with a different density, thickness and
composition.
 Furthermore the earth's crust is not one continuous
layer.
 It is broken into many sections known as plates. Some
plates are quite small while others are quite large.
Earth’s Interior
 They all float and move on top of the molten
asthenosphere.
 When these plates push together and when they pull
apart they create "tectonic forces".
 It is interesting to note; without this liquid layer called
the asthenosphere we would not experience
earthquakes or volcanoes.
 The Earth’s Interior (Worksheet 1.1)
Plate Tectonics
Plate Tectonics
 https://www.youtube.com/watch?v=lJiAUvB1vEU
Patterns of Plate Movement
 When any objects move separately, we either get
movement towards each other or movement away from
each other
 Regarding plate tectonics, we call this movement
towards or away as compressional or tensional
 Compressional Forces occur where two tectonic
plates come together, they compress & squeeze
against each other causing rock layers to bend, warp,
or be pushed upwards .
 Subduction Zones sometimes occur where
compressional forces result from two plates colliding.
Plate Tectonics
Plate Tectonics
 Tensional Forces occur where two tectonic plates are
pushed apart (stretched). The tension is created as
the plates move away from each other which
sometimes forms a trench as one plate drops
downward.
 Ridge Zones sometimes occur where two plates move
apart. The magma rises between the plates and forms a
ridge.
Plate Tectonics
Plate Tectonics
Plate Tectonics Lab
 Major Mountain ranges tend to coincide with
subduction zones at the boundaries between two
converging plates.
 The tremendous compressional forces literally fold the
thin crust in to mountains over millions of years.
 Volcanoes can occur at subduction zones or at ridge
zones.
 At subduction zones the compressional forces
sometimes leave a crack in the crust that allows the
magma to reach the surface.
 At ridge zones the plates are moving apart which
allows magma to reach the surface from the
asthenosphere.
 Because of the excessive number of active volcanoes on
the coast around the pacific ocean it is known as the
Pacific Ring of Fire.
 Earthquakes often occur at transform zones where
the plates are moving beside each other instead of
toward or away from each other.
 Look Closely at figure 1.10 on page 12 and you can see
transform zones where the plates are moving side by
side.
 Notice that subduction zones occur where the tectonic
plates are moving towards each other while Ridge
zones occur where the plates are moving apart and
transform zones occur where plates are moving side by
side.
 Notice that the Americas (North American Plate and
South American Plate) are moving away from Europe
and Africa (Eurasian Plate and African Plate.
 Plate Tectonics Lab