How did Block Island form? How is it changing now? What will it look like in the future?

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How did Block Island form?How is it changing
now?What will it look like in the future?
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Block Islanda product of Erosion and Deposition

• weathering the change/breakdown of rock on
  Earths surface
• erosion movement or transportation of weathered
  materials
• agents of erosion gravity, wind, glaciers, and
  water (ocean currents and waves, streams,
  groundwater)

• deposition the leaving behind of materials
  carried by erosion
• agents of deposition gravity, wind, glaciers and
  water (same as for erosion)

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Background Information
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Wind Erosion

• Wind erodes land by carrying away rock particles
• mostly smaller particles sand and rock dust
  (silt and clay) are carried by wind

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Wind Deposition

• deposition by wind most common dunes (mounds
  of wind-blown sand)
• gentler slope of a dune faces wind

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Slumping erosion from groundwater and gravity
Large block falls off a cliff or bluff forms- sea
cliffs/bluffs
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Erosion by ocean waves

• physical weathering force of the water weathers
  and erodes the shoreline affecting beaches

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Ocean Wave Deposition

• beaches deposits of sand or larger particles on
  ocean (or lake) front
• beach changes seasonally remember beach
  profile??
• berm top of the sloping surface (above is part
  for recreation)
• sand bar long underwater ridge of sand carried
  away from beach

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Wave anatomy

• Wavelength distance between 2 crests or 2
  troughs
• Wave height (2 X amplitude) height from trough
  to crest
• How could you determine these??

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Wave characteristics

• Wave period the time is takes for a wave to pass
  a fixed point
• Wave frequency the number of waves that pass by
  in a given time.
• How could you determine these??

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Wave characteristics 2

• Wave speed the distance traveled by a given
  point on the wave (such as a crest) in a
  given interval of time. In equation form

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Longshore Currents

• general movement of sand along beach in same
  direction that waves hit shore
• longshore current movement of water and sediment
  parallel to, and near shoreline
• animation http//www.learnnc.org/lp/multimedia/14
  706
• Real video http//www.youtube.com/watch?vl70ioFT
  D6TYsafeactivesafety_modetrue

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Features from longshore current deposition

• Headland land surrounded by water on three sides
  
• spit long narrow deposit of sand connected at
  one end of shore
• tombolos ridge of sand deposits connecting
  islands to mainland

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Glacial Erosion

• Glaciers are rivers of ice slowly flowing,
  moving sediments and changing the surface and
  shape of the ground beneath it
• Last glacial ice age in NE ended about 18,000
  years ago

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Glacial Deposits

• glacial till ? unsorted glacial materials
• stratified drift ? sorted and deposited in
  layers by meltwater

Glacial erratic
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Features from glacial deposition

• Glacial moraines landforms made from glacial
  till
• terminal (end) moraine deposited at the end

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More features from glacial deposition

• moraine

• erratics large boulders transported by
  glaciers

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More Glacial Deposition features

• drumlins low tear-shaped mounds of till
• kettles depressions left from melting ice

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Stratigraphy

• Stratigraphy is the study of strata, or layers
• Stratigraphy can tell us about how the soil was
  deposited, they are clues to the lands origin

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Your tasks in the field(gathering evidence for
your big 3 questions)
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Task 1 create a topographic map of Block Island
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Another look
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Converting an island into a topo map
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Hawaii topo
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Creating a Contour/Elevation Map

• Use your elevation observations to determine the
  higher/lower points on BI
• Draw contour lines onto the map

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Try a sample map
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Task 2 Sieving soil, to tell particle size

• You will collect soil samples to sift with
  sieves
• These will separate the soil into different sized
  particles gravel, fine gravel, coarse sand,
  fine sand and silt and clay
• Sieving Purpose this tells how the soil got there

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Soil sizes
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Soil horizons, or strata
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Sand, different sizes deposit by different ways

• How is sand classified? If you classify sand by
  size, you look at the diameter of each sand
  particle. Very coarse sand, like you might see in
  a sand box, has the largest particles. The
  diagram below shows the actual size of sand
  particles from 0.5 to 2 mm in diameter.
• very fine   0.05 - 0.01mm
• fine   0.1 - 0.25mm
• medium   0.25 - 0.5 mm
• coarse   0.5 - 1 mm
• very coarse   1 - 2 mm

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Conclusions from sieving and soil profiling

• The bigger the sand particle size, the steeper
  the beach typically is
• Steep, big particle beaches are formed from
  strong deposition forces and erosion
• This makes them less stable
• Flat, small particle beaches are formed from
  gentle deposition forces, and are more stable

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Task 3 create a beach profile

• Beach profiling provides clues as to
• how the beach formed
• how is it changing now

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(No Transcript)
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General beach anatomy
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How does the beach change over time?

• The shape of the beach is in continual change due
  to the weather and tides.
• In calmer weather with regular tides, sand is
  gradually deposited onto the beach from sand bars
  out in the ocean, dunes and berms may form.
• In stormy weather, the beach erodes and sand is
  brought from the beach to sand bars, which run
  parallel to the shore (provides better surfing).

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More of the same
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Task 4 Measuring wind speed and direction

• Wind speed use an anemometer
• Wind direction use the compass

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Good luck geologists!
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Review Fill in the characteristics for each
type of change
EROSION DEPOSITION