Transcript Natural Processes operating in a named

A process is a sequence of events that
maintains or modifies the environment.
Natural processes operate below and
above the earths surface.
Those below tend to form new land,
those above wear it away.
Land eroding
Land forming
PROCESSES BELOW THE EARTHS SURFACE: LAND
FORMING
• Convection Currents within the mantle
• Subduction of one plate under another.
• Upward Folding of sedimentary rocks to form
mountains * Outcome
• Volcanic eruptions producing new land and recent
deposits * Outcome
• Earthquakes may cause new land to appear or land
to be uplifted* Outcome
VOLCANIC ERUPTIONS PRODUCE NEW LAND:
MONTSERRAT
CHRISTCHURCH EARTHQUAKE
The block of land south of the fault slid up the fault surface by as
much as 2.5 metres on the section of fault near the Avon-Heathcote
estuary. This raised part of the Port Hills and part of southern
Christchurch. The land has gone up as much as 40 centimetres around
the western side of the Avon-Heathcote estuary. The Port Hills have
gone up by varying amounts,
from about 5 centimetres
under Lyttelton Harbour to
a maximum of about
25 centimetres at the base
of the hills near the
Heathcote valley.
Fold mountains are formed when two plates move together (a compressional
plate margin). This can be where two continental plates move towards each other or a
continental and an oceanic plate. The movement of the two plates forces sedimentary
rocks upwards into a series of folds. Fold mountains are usually formed from
sedimentary rocks and are usually found along the edges continents. In NZ, the
Southern Alps are an example.
http://www.s-cool.co.uk/gcse/geography/tectonics/revise-it/fold-mountains
Rock Types: Igneous
Sedimentary
Metamorphic
PROCESSES ABOVE THE EARTHS SURFACE:
WEARING AWAY THE LAND
•Weathering
•Mass Wasting
•Erosion, transportation and deposition by
rivers, wind, glaciers and the sea **
INTERACTION OF PROCESSES BELOW AND
ABOVE THE EARTH
Example: Volcanic eruptions produce loose, unconsolidated
deposits of tephra
which are
transported downhill by wind and rivers and deposited on
flood plains and in the sea.
Example:
WEATHERING IS DEFINED AS "THE BREAK DOWN OR ALTERATION OF
ROCK IN ITS NATURAL OR ORIGINAL POSITION AT OR NEAR THE
EARTH'S SURFACE.
Weathering is different from erosion, which usually includes the transportation of the
disintegrated rock and soil away from the site.
• 1 Frost shattering, sometimes aptly called freeze-thaw, is the most widespread form
of weathering in cold climates. It occurs when crevices and joints in rock fill with
water. During the night, this water freezes, expanding by 9% and exerting great
pressure on the surrounding rock. The alternating freeze-thaw processes weaken the
joints, and cause pieces of the rock to be broken off.
• 2 Salt crystallization occurs on coasts. If water entering the cracks and pores in
rocks is at all saline, then salt crystals are often left as it evaporates. The increasing
size over time of these crystals puts the surrounding rock under pressure.
• 3 Exfoliation is the expansion and contraction of the outside layer of rock due to
temperature change or wetting/drying and when this is repeated many times, the
outer skin of the rock peels away in a way similar to that of an onion. Exfoliation
leaves rounded boulders.
• 4 Tree roots may sometimes grow along bedding planes or joints in rocks, detaching
blocks of rock.
• Chemical weathering happens when the minerals of which the rock is
made are changed, leading to the disintegration of the Rock.
• 1 Oxidation, as the name suggests, occurs upon contact of the rock
with oxygen, from the air or from water. A common effect is the
rusting of rocks containing iron, as blue-grey becomes reddish-brown
when ferrous compounds are oxidised.
• 2 Hydration simply involves the absorption of water into the existing
minerals of the rock, causing the expansion of the mineral, leading to
eventual weakening.
• 3 Carbonation is a result of the reactions of rainwater and carbon
dioxide to produce carbonic acid (H2CO3), which slowly dissolves
any rocks made of calcium carbonate, such as limestone.
Mass Wasting or Mass Movement:
material moving downhill under
the influence of gravity.includes- falls, slides, slumps,
flows.
WELLINGTON LANDSLIP SATURDAY, 1 JUNE ‘13
Kingston and Berhampore suburbs: see notes.
Task: put the information into a systems diagram
WIND ACTION
A)SURFACE CREEP : FIRST LAYER OF HEAVY PARTICLE AT LOWER HEIGHT.
B) SALTATION : SECOND LAYER OF PARTICLE WITH DANCING MOTION.
MOVEMENT UP TO 2 M HEIGHT. SALTATION ACCOUNT FOR
ABOUT 95% OF BULK SAND TRANSPORTATION. THE PARTICLES MOST READILY
MOVED BY WIND HAVE DIAMETERS OF 0.1 TO 0.2MM (FINE SAND). A THRESHOLD
WIND VELOCITY IS NECESSARY TO INITIATE SAND MOVEMENT. TYPICALLY THIS IS OF
THE ORDER OF 20 KM/H.
C) SUSPENSION : THIRD LAYER OF SUSPENDED PARTICLE ABOVE 2-4 M
HEIGHT, INVOLVES PARTICLES OF SMALLER THAN 0.15 MM SIZE.
WIND DEPOSITION-OUTCOME=DUNES
Wind can deposit sediment when its velocity decreases to the point where the
particles can no longer be transported or when the grains hit a dune or dune
vegetation. They then form sand dunes.
• Sand dunes are asymmetrical mounds with a gentle slope in the upwind direction
and steep slope called a slip face on the downwind side. Dunes migrate by erosion
of sand by wind (saltation) on the gentle upwind slope, and deposition and sliding
on the slip face.
GLACIER: FRANZ JOSEF
•W
•
West Coast of the S. Island
•
TASK:
•
Examine relationship between
•
advance/retreat and
•
precipitation. Graphing.
Franz Josef Glacier has a high-altitude snowfield of 20 square kilometres,
and Fox Glacier 32 square kilometres. These funnel vast amounts of ice
into narrow valleys. The effect is like pressing on a tube of toothpaste. The
ice is pushed right down the steep valleys to the coast, at speeds of
several metres per day. The fast-moving ice does not melt until it is near
sea level, where there is warmer air and frequent heavy rain.
Both the Franz Josef and the Fox glaciers are very sensitive to variations
in climate. Even small changes in snowfall can result in substantial changes
in the position of the terminus. There is a 5–6-year delay between a
change in snowfall in their upper basins, and an advance or retreat of
their terminus.
• http://ees.as.uky.edu/sites/default/files/elearning/module13swf.swf
for animation of advance and retreat.
RIVER ACTION
http://www.youtube.com/watch?v=E6sWiPAu708
http://www.slideshare.net/gabr0088/river-erosion-and-transport
http://www.slideshare.net/jacksonthree/revise-rivers
Rivers are the most widespread agents of denudation and deposition. The amount of erosion, transportation and deposition of the
river is dependent on the energy of the river which in turn is dependent on: The gradient of the slope The volume of water The
shape of the channel Generally, the volume of the river increases from the source to the mouth.
River Erosion involves 4 processes:
•
•
•
•
Abrasion/Corrasion: The wearing away of the sides and the bed of a river by the impact of the load.
Hydraulic Action: Erosion by the force of moving water.
Atrrition: The breaking down of the load by particles hitting against each other.
Solution/Corrossion: When minerals dissolve in water.
River Transport A river transports its load in 4 main ways:
•
•
•
•
Traction: The rolling of huge particles along the bed.
Saltation: The bouncing of particles on the bed of the river
Suspension: The movement of particles held up by river turbulence.
Solution: The movement of particles dissolved in water.
River Deposition
Deposition takes place when a river has insufficient energy to transport its load. It takes place at all stages of a river.
Larger particles are deposited first. Deposition is greatest in the lower course of a river. It is also greater during floods. Deposition
will occur when the speed of a river is reduced. This may happen in:
SEA: COASTAL EROSION, TRANSPORTATION AND
DEPOSITION IN THE OMAHA ENVIRONMENT