Coastal

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Coastal Arid Geomorphology

• Lab 9

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Coastal GeomorphologyConcepts

• Principal Forces for Erosion (5)
• Landforms
• Barrier Island/Lagoon
• Barrier Spit
• Beach
• Coral Reefs
• Tombolo
• Wave-cut arch platform

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Coastal GeomorphologyPrincipal Forces for Erosion

• 1. Tides
• Oscillations of ocean water gravitational pull
  of the Moonand Sun
• 24 hours High-Low-High-Low tide periods
• 2. Sea-level changes
• Rising/Falling results from tectonic activity or
  amount of water in ocean
• Creates emergence (above water) and
  submergence(below water) coastlines

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Coastal GeomorphologyPrincipal Forces for
Erosion (cont)

• 3. Waves
• Most important erosional force
• 4. Currents
• Large volumes of water moving horizontally
• Consistent winds create currents
• Longshore currents transport sediment down a
  coastline (helps in formation of beaches)
• 5. Stream Outflows
• Spills sediments out into the ocean and adds
  material to beaches
• Deltas often form at the mouth of rivers why?

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Coastal GeomorphologyLandforms Barrier
Islands/Lagoons

• Barrier Island
• Long, narrow, low island that lies parallel to a
  shoreline.
• Buffers the mainland from storms and large
  waves.
• Lagoon
• Nearly isolated body of water, separated from
  sea by the barrier island.
• Low-energy waves and relatively calm area, so
  sediments may accumulate.
• Mudflats, marshes, swamps

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Coastal GeomorphologyLandforms Barrier Spit

• Barrier Spit
• Coastal barriers thatextend into open
  water,attached to themainland at one end.
• Can develop into abarrier island if itbecomes
  separatedfrom the mainland.

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Coastal GeomorphologyLandforms Beaches

• Beaches
• Made of eroded continental material (sand,
  gravel, rock fragments) that are washed to the
  sea by streams.
• Sediment gets suspended in sea water and is often
  transported further down the coastline by
  longshore currents.
• Longshore currents provide a continual
  onshore-offshore movement which pushes the sand
  along the beach edge. Often called littoral
  drift.

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Coastal GeomorphologyLandforms Coral Reefs

• Reef formation first determined by Charles
  Darwin, mid-1800s.
• Occurs in tropical zone approx 30oN to 30oS.
• More coral species live in the Pacific than
  anywhere else!
• Fringing Reef
• Forms along shoreline of volcanic island (hot
  spot) it likes the warm waters!
• Barrier Reef
• Island begins to sink or erode, but reef
  continues to grow upward. Lagoon is created
  between the top of the reef and the sinking
  island.
• Atoll
• Island sinks/erodes below sea level, reef
  continue to grow upward.
• If a broken circle of reef, it is likely due
  to storm action.

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Coastal GeomorphologyLandforms Tombolo

• Tombolo
• A narrow piece of land between the shore and an
  island, or between two islands.
• Forms because wave refraction around islands
  causes sand and sediment to build up in a linear
  formation where the waves meet (around the
  backside of the island).

Goat Rock Beach, CA
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Coastal GeomorphologyLandforms Wave-cut Arches
Platforms

• Wave-cut Arches
• Formed by wave action which erodes
  less-resistant rock from an outcrop.
• Wave-cut Platforms
• Formed after waves hit against a cliff face,
  causing undercutting.
• Most obvious at low tide when they become
  visible as huge areas of flat rock.
• An extreme environment (for marine life)
  because of continual wave action.

PLATFORM
ARCH
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Deserts Arid GeomorphologyConcepts

• Locations
• Typical Conditions (4)
• Principal Forces (2)
• Landforms
• Alluvial Fan/Bajada
• Inselberg
• Playa
• Buttes, Pinnacles, Mesas
• Dunes

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Deserts Arid GeomorphologyLocations
0o
0o
0o
0o
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Desert Arid Geomorphology4 Typical Conditions

• Sparse cover of vegetation and soil
• Bedrock is exposed
• Impermeable surface layers
• This increases the erosion potential of
  rainstorms!
• Rain is infrequent, but short-lived intense
• Causes dry streambeds to fill quickly flow
  rapidly
• Flash flooding fast erosion!
• Interior drainage centripetal
• Ephemeral streams flow to the bottom of basin
• Alluvium is deposited and water
  evaporates,sometimes leaving behind a salt layer

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Deserts Arid GeomorphologyPrincipal Forces for
Erosion

• 1. Water
• Water may be scarce, but rain/thunderstorms are
  often intense.
• Rivers or floodwaters cut into the landscape,
  often creating canyons.
• 2. Wind
• Often removes sand/siltfrom areas,
  exposingbedrock to the erosionalpower of water.

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Desert Arid GeomorphologyLandforms Alluvial
Fan

• Alluvial Fan
• When streams come out of steep canyons
• the velocity of the stream drops dramatically,
  and
• the slope of the riverdecreases.
• Therefore, alluvium isdeposited!
• Edges of the fans maybe clearly defined.
• Bajadas are formed whenmultiple alluvial fans
  joinalong a mountain front

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Desert Arid GeomorphologyLandforms Inselbergs
Playas

• Inselberg
• Isolated hill/ridge, steep-sided
• Formed when less-resistantmaterial is eroded
  away frommore-resistant rock (often anintrusive
  formation).
• Example Uluru (Ayers Rock), AU
• Playa
• Dry lake bed
• Found at lowest pointof basin
• Recognizable by driedmud, often covered w/crust
  of salt

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Desert Arid GeomorphologyLandforms Pinnacles,
Buttes, Mesas

• Pinnacles
• Isolated hill with steep sides and pointed or
  flat top
• Caprock (resistant) remains while softer rock
  is eroded away
• Typical of southwest U.S.
• Buttes
• Larger than a pinnacle, flat top
• Example Chimney Rock, NE
• Mesas
• Larger than a butte, smaller than aplateau. Flat
  top.

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Desert Arid GeomorphologyLandforms Sand Dunes

• Shape formation depends on
• Amount of sand available
• Persistence direction of wind
• Presence of vegetation
• With little vegetation can be movement over time
• 4 main shapes
• Barchan
• Transverse
• Longitudinal
• Blowout

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Desert Arid GeomorphologyLandforms Sand Dunes

• Barchan
• Limited supply of loose sand
• Crescent-shaped
• Horn points downwind
• Wind blows constantly in a single direction
• Migrates downwind over long time

Which way is the wind blowing?
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Desert Arid GeomorphologyLandforms Sand Dunes

• Transverse
• Less uniform than Barchan
• More supply of loose sand
• Maintains general crescent shape
• Usually forms interconnected ridges of sand

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Desert Arid GeomorphologyLandforms Sand Dunes

• Longitudinal
• a.k.a. Seif
• Wind directions shifts back forth
• Long parallel ridges

Egypt
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Desert Arid GeomorphologyLandforms Sand Dunes

• Blowout
• Wind erosion
• Scoops out sandand rock,creating
  closeddepressions
• Depressionsmay fill withwater