Transcript Wind direction

By Wind and Waves
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Review
Any natural process that removes sediments
and carries them away from one place to
another is called erosion.
Gravity is the driving force behind all
erosion.
Everything on earth is constantly being
pulled toward the earth’s center by gravity.
Any particle of matter that is free to move is
going to move downward due to gravity
unless some other force interferes.
Wind Erosion
• Wind erodes dry land much more
effectively than it does moist land (more
plants with roots to hold the soil).
• As the wind erodes land it carries rock
particles along with it, mostly sand, silt, and
clay.
• Sand material is moved along by a number
of jumps and bounces, much how a pebble
is moved along the bottom of a stream bed.
• The wind causes friction on sand grains to
lift them into the air. Gravity pulls them
down to the surface.
• Sand grains, which cause most of the
abrasion, do not rise higher than about 1
meter, and they move in the same direction
the wind is blowing.
• Dust particles (silt and clay) can be carried
along great distances and at greater heights
than sand particles.
Effects of wind erosion
• Abrasion is the weathering of rock particles
by the impact of other rock particles.
• In areas where there are strong, steady
winds, large amounts of loose sand, and
relatively soft rocks, abrasion causes a great
amount of erosion.
• Pebbles and small stones exposed to wind
abrasion show surfaces that are flattened
and polished on two or three sides.
• Rocks smoothed this way are called
ventifacts.
• Particles that have been moved by the wind
are well rounded by the repeated impact of
grain against grain, and when examined
with a magnifier, their surfaces have a
frosted appearance.
• Outcrops of rocks in arid regions undergo
the greatest amount of erosion close to their
base, because particles transported by the
wind remain close to the ground.
DEFLATION
Removal of fine particles by wind leaves
hollows behind (Deflation Hollows)
Also leaves a surface of closely packed
stones (DESERT PAVEMENT)
SAND DUNES
are ridges of wind
deposited sand
- Usually 3 to 15
metres high, but can
reach 180 metres
- A continuously
changing dune is
ACTIVE
Corbis Digital Stock
The formation of
dunes depends on:
- amount of sand
- speed and
direction of wind
- occurrence of
vegetation
Corbis Digital Stock
wind direction
BACKSLOPE
SLIPFACE
crest
angle of
repose
TYPES OF SAND DUNE
1.) BARCHAN
- most common type
- crescent-shaped
backslope
slip face
Wind direction
2.) TRANSVERSE DUNES
• low sand ridge at right angles to the wind
direction
• may form because of large amounts of sand
wind
3.) LONGITUDINAL DUNES
• low sand ridges parallel to the wind direction
• may form because of a limited amount of sand
• also known as seif dunes
wind
LOESS
• Finely
textured
sediment (silt)
wind-blown
long distances
• Wind-blown
glacial debris
formed large
deposits
Wave Erosion and Deposition
• Energy from waves transfers to land and
causes erosion to form erosional features
such as cliffs.
• Sand is the product of this erosion. The
type of sand depends on the material being
eroded (typically quartz and coral—white
sand, or basalt—black sand).
• Sand material is transported by waves and
currents to form beaches and other transient
coastal landforms.
WAVES
wave length
crest
wave
height
trough
particles in
waves follow a
circular pattern
At the shoreline
• Water becomes shallow, wave height increases because
wave length decreases
• Waves become steeper, then collapse (breakers)
• Surf - sequence of
breaking waves
• Swash - water sliding
up beach
• Backwash - water
flowing back down
beach to sea
Wave refraction
Bay
Headland
• Waves arriving at bays are slow (deposition)
• At headlands, faster (erosion)
• A sequence of
features is
produced as
headlands are
degraded
• Sea cliffs
• Waves erode base
-undercutting
the cliff
retreats
• Also produces
sea caves
• As cliffs retreat
produces a wavecut platform
• Headlands
may be eroded
back leaving a
remnant (stack)
stack
Longshore drift
• Waves arrive at a coast at
an angle (swash)
• Backwash returns at 90
degrees
Sand is moved along the beach = longshore
drift or longshore current
Coastal deposition
• Result of longshore
drift and a lot of
sediment
• produces extensions
of deposit from the
shoreline
spit = curved extension
• May grow across
a bay (baymouth
bar or barrier
beach)
• May link an island
to the main land
(tombolo)
Sandbar
• Off-shore sand deposit that lies just below the water
surface
Barrier Island Coasts
• Occur on low lying coasts with
gentle gradients
• BARRIER ISLANDS - low
ridges of sand built by waves
– behind the islands are lagoons
– shallow water with tidal deposits
• TIDAL INLETS - gaps
between the islands