UNIT 4: DEPOSITION PROCESSES ON A COAST
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Transcript of UNIT 4: DEPOSITION PROCESSES ON A COAST
UNIT 4: DEPOSITION PROCESSES ON A COAST
Page 6 UNIT 4: DEPOSITION PROCESSES ON A COAST HOW BEACHES AND
DUNES FORM Beach are built by CONSTRUCTIVE WAVES - gentle waves
that push sand up onto the beach building up a feature called a
BERM at the shore line - wind then blows the sand inland where it
is trapped by vegetation in the dunes. As long as the weather is
calm, the waves will continue to push sand up onto the beach &
the beach will grow as incoming sand from the sea is available.
Sand cycle animation; http://www. duedall. fit
THE BEACH SAND CYCLE IN CALM WEATHER - In periods of relatively
calm weather the waves are CONSTRUCTIVE swash is more powerful than
backwash and the beaches builds up as sand is deposited. IN STORMY
WEATHER - In periods of stormy weather with DESTRUCTIVE waves
(backwash more powerful than swash)the beach is eroded and the sand
moves out to an offshore sandbar.c A typical Perth beach in
mid-summer Wind deflates the beach blowing sand inland Constructive
waves deposit sand on the berm BERM SAND ROCKS Sand moves toward
thebeach WINTER SUMMER THE BEACH SAND CYCLE A typical Perth beach
in mid-winter
IN STORMY WEATHER - In periods of stormy weather with DESTRUCTIVE
waves (backwash more powerful than swash)the beach is eroded and
the sand moves out to an offshore sandbar. A typical Perth beach in
mid-winter GALE FORCE WINDS Dunes absorb the power of the waves
SAND ROCKS Sand is deposited at an offshore bar THE RESULTS OF
LONGSHORE DRIFT - SPITS
Moving sand along a beach spreads out into the sea where the land
bends Look at this animation to see how a spit forms: FORMATION OF
A SPIT Points A, B, and C show the progression of the spit's
formation. The curved ends are explained in point 6. 1. Fetch -
direction of prevailing winds (and therefore waves) in approaching
the beach. 2. Direction of Long-Shore Drift. 3. Salt Marsh 4.
Original Coastline 5. River Estuary 6. Short term changes in wind
and wave direction causing the curved ends to the spit. LONGSHORE
DRIFT SALT MARSH View this animation of a baymouth bar
Tombolo Development Tombolo - Santa Cruz, CA COASTAL SAND DUNES
Look at this website Sand movement on a dune
These occur where sand is being constantly supplied by onshore
winds that blow across sandy beaches. The most common dunes on the
coast are parallel dunes. They occur with strong onshore winds
& lots of fine sand. These dunes are useful energy absorbers in
that during storms they act as a buffer protection zone from
serious coastal erosion during winter storms. If vegetation is
removed from the dunes, they blow inland in blow-outs. This can
cause serious management problems. Look at this website Sand
movement on a dune