Download Wave Erosion

River Erosion
• Erosion shapes the land in different ways as the
river moves from its source to its mouth:
• Near the source of a river, in the upper course,
erosion is vertical (downward). This is because
the water is being pulled downwards by gravity.
This forms deep V-shaped valleys.
• Near the mouth of a river, in the lower course,
erosion is lateral (horizontal or sideways). This
forms a wide river channel.
Wave Erosion
• Wave erosion occurs when the wind moves over the
ocean to produce waves and currents which erode the
adjacent land.
• Wave action is the greatest during storms and the least
when the weather is calm.
• Abrasion is the grinding and rubbing action of water
loaded with sand and rock fragments which can wear
away the surface of rocks. Waves can crack rocks by
flinging other rocks against them, and once a crack has
a been formed, it can be widened as water and smaller
rocks are forced into it. Over time, the destructive power
of water can transform a rocky cliff into rubble.
http://cse.cosm.sc.edu/erth_sci/Coasts/Erode.htm
Flatrock
Wave Movement
• Water waves are characterized by their
height, their length, and their period. The
wave height is the distance between the
trough (lowest part) and crest (highest
part) of the wave. The wave length is the
distance between wave crests. The wave
period is the time for two consecutive
crests to pass a point.
Off Shore Supply Boat
Refraction
• Refraction is the bending of wave fronts as they
approach the shore.
• When a wave approaches the shore at an angle, the
near-shore stretch of wave front reaches the shallow
water first and is, therefore, slowed down first.
• This decrease in speed causes the wave front to bend or
refract because the deeper water portion of the wave
continues to move at its original speed.
• As a result, the waves near shore tend to approach the
coast nearly head-on while those in deeper water
continue along their original course.
• Wave refraction has its greatest effect on irregular
shorelines with deep bays and projecting headlands.
http://walrus.wr.usgs.gov/infobank/programs/html/school/moviepage/22.01.08.html
“Jaws”
Sea Spit
• A spit is a deposition landform found off coasts.
• A spit is a type of bar or beach that develops
where a re-entrant occurs, such as at a cove,
bay, ria, or river mouth. Spits are formed by the
movement of sediment (typically sand) along a
shore by a process known as longshore drift.
Where the direction of the shore turns inland
(reenters) the longshore current spreads out or
dissipates. No longer able to carry the full load,
much of the sediment is dropped. This causes a
bar to build out from the shore, eventually
becoming a spit.
http://en.wikipedia.org/wiki/Spit_(landform)
Long Point located on the north shore of Lake Erie
Examples of wave erosion
formations
• Sea cliffs form when
a rocky shore erodes
at approximately the
same rate throughout
an area. This results
in a steep walled
structure. The cliff
moves landward as
the waves attack its
base.
Examples of wave erosion
formations
• Sea caves form when
waves attack weak
portions of a cliff. The
pounding and cutting
of the waves on the
weak rock cause
large holes to be cut
from the cliff. Notice
the small sea cave in
the picture above.
Anthony Island, Trinity Bay
Examples of wave erosion
formations
• Sea arches are
formed when waves
cut completely
through a sea cave.
This can form a
natural arch or bridge.
Cape Broyle
Examples of wave erosion
formations
• Sea stacks are
formed when sea
arches are eroded
through the center
causing its middle to
collapse. The
remaining columns
become sea stacks.
Eventually the stacks
are eroded and they
are barely visible
above the water.
Headland Erosion