Natural Systems
INTERNAL FORCES
Earth is composed of three
distinct layers:
• Core
• Mantle
• Crust
Pangaea – supercontinent
• Theory that states that the Earth’s outer Crust is divided
into oceanic and continental plates that move as a result
of convection currents in the Earth’s mantle.
Plate Tectonics Theory
• The crustal plates are separated by plate boundaries,
(also sometimes referred to as plate margins).
• There are three types of plate boundaries,
• Constructive/ divergent
• Destructive/ convergent
• Transform / neutral
Plate Boundaries
• These plates move apart or diverge
from each other.
• When this happens with two oceanic
plates, new ocean crust is formed. Eg.
Mid Atlantic Ridge
• Upward movement of magma pushes
the oceanic plate upwards, then drags
the plates apart, causing the plate to
break. Magma moves into the fissure
and solidifies, the process repeats
itself and the ridge is formed.
Constructive/Divergent
•
•
•
These plate boundaries move towards,
or converge upon, each other.
This coming together of the plates
causes the denser plate to sink; this is
called subduction.
Eg. Nazca Plate (oceanic) & South
American Plate (continental) – oceanic
plate sinks and melts – forming magma
chambers that move up through the
surrounding material which either cool
or break through the surface as a
volcano.
Destructive/Convergent
• Eg 2. Caribbean Plate (oceanic) & American Plates (oceanic) – the
older, more dense oceanic plate will subduct under the other. The
older plate melts as it reaches higher temperatures, and magma
chambers are formed. The magma is less dense than the surrounding
materials and so rises, moving through and fracturing rock above it.
If it reaches the surface and has not cooled, it will break through and
cause volcanic activity which, over time can cause the formation of
an island chain – Lesser Antilles.
• This type of movement cause the formation of volcanic island, as
well as earthquakes, and it destroys sea bed.
• Eg 3. Indo-Australian plate (continental) and the Eurasion
Plate (continental) led to the creation of the Himalayas,
the site of Mount Everest.
• Plates slide past each other. Eg. San Andreas Fault is a
result of the Pacific Plate and North American Plate
sliding past each other – this leads to the occurrence of
earthquakes.
Transform/Neutral
The movement of the Earth’s crustal plates, as stated earlier,
can give rise to many natural phenomena including;
• Mountains
• Volcanoes
• Earthquakes
• Mountains are large landforms with steep and rugged
terrain that are 600m and above the surrounding
landforms.
• Fold mountains are formed at the site of two convergent
plate margins. Tectonic forces compress the plates toward
each other, and this forces the sediment on the edges of
the boundaries upward, thus forming fold mountains.
Fold Mountains
• Eg 1. The Himalayas – Indo-Australian and Eurasian
plates
• Eg 2. The Andes – Nazca and South American Plates
• Eg 3. The Jamaican Blue Mountains – Caribbean and
South and North American plates
Fold mountains
• Volcanoes are landforms that are formed when the Earth’s
surface cracks open and through that opening comes lava,
rocks, and various gases.
• Magma moves beneath the Earth’s crust, and escapes (as
lava) through fractures, or weak spots in the crust. In the
absence of these fractures, the magma solidifies and
forms intrusive landforms. This sold magma is termed
plutonic rock.
Volcanoes
• Batholith – this is a large intrusive landform, formed when magma cools
deep beneath the Earth’s surface, eg. Basalt and granite.
• Sill – plutonic rock that has come between two layers of rock, but does
not cut across rock. It is horizontal and roughly parallel to the surface.
• Dyke – magma that has solidified in a fissure/fracture across many rock
layers.
• Laccolith – dome shaped plutonic rock that forms from viscous magma
that has been injected between two layers of rock. These are shallow,
closer to the surface.
• Over time, erosion exposes these landforms.
Intrusive Volcanic Landforms
• Viscosity depends on the silica content of the magma.
• High silica content
high viscosity
thick, slow moving lava.
This is called acid lava.
• Low silica content
low viscosity fluid lava that spreads more
readily, and is of a higher temperature. This is called basic lava
• Gases, eg. CO2 and sulphur dioxide are dissolved in magma. The
gases expand as pressure is lowered as the magma moves upward.
Basic magma allows gases to escape easily, however, acidic Lava are
thicker, and don’t allow for easy escape of gases, which leads to more
violent eruptions.
• Lava plateau – a flat, raised platform bound by steep
slopes. This is formed around basic/basaltic lava
volcanoes. Because the lava is very fluid and has a high
temperature, the lava spreads quickly. The repeated
process of gentle eruptions allows for the outpouring of
lava, and over time, this covers the landscape.
• Eg. Deccan Plateau in India
Extrusive Volcanic Landforms
• Volcano – a landform formed when magma escapes
through a vent in the Earth’s surface. How the lava, ash
and cinder deposit determines the structure of the cone.
• Lava escapes through an opening called a crater. In an
instance where the crater gets blows off, the subsequent
landform is called a caldera. If water collects in the
caldera, this is called a caldera lake.
Extrusive volcanic landforms
• Acid lava cone – steep sides and narrow base, can lead to
formation of volcanic plug
• Basic lava cone – gentle slopes, broad bases, lower
heights
• Ash and Cinder cone – explosive eruptions lead to gently
sloping base with steep summit.
• Composite cone – alternate layers of ash and cinder and
lava
Types of Volcanoes
• In the mantle, rock is melted, and thus is in a liquid form.
When magma cools, and forms crystals, igneous rock is
formed. Igneous rock can form underground (magma
cools slowly) or above ground (magma cools quickly).
• Igneous rock can turn into sedimentary or metamorphic
rock.
The Rock Cycle
• Sedimentary rock is formed from pieces of other rocks.
When rocks break off into small pieces, water and wind
transport the small particles and they are deposited in a
layer. After many years, the particles become cemented
together and form sedimentary rock.
• Metamorphic rock can be formed from sedimentary rock
when it becomes heated. After many layers of
sedimentary rock form, the pressure from the layers
creates heat that bakes the rock, which changes its
mineral make-up.
• Earthquakes are vibrations of the Earth’s crust caused by
the sudden release of stored energy when rocks are
displaced along a fault line.
• There is a large amount of friction between plates, and
the friction is stored in rocks. A lot of friction is applied
to rocks, and when they snap, they release all the energy
suddenly, and this moves through the crust as seismic
waves.
Earthquakes
• Focus – the source in the earth’s crust where the
Earthquake orginiates
• Epicenter – this is the point directly above the focus, on
the earth’s surface. The earthquake is strongest at the
epicenter and weaken as you move further out.
Earthquakes