Transcript Coasts - South Kitsap School District

Coasts
 I can distinguish between primary and secondary coasts.
 I can describe different types of beaches.
Types of Coasts
 Primary coasts
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Effect of ice ages (glaciers)
Effect of sediment carried by rivers
Effect of wind
Effect of volcanic activity (lava flows)
Effect of tectonic activity (uplift & subsistence)
Erosion due to running surface water
 Secondary coasts
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Erosion due to the movement of the sea
Deposition of sediments due to movement of sea
Stabilization due to marine plant growth
Finding the best beach to sunbathe
or snorkel: WA shores and beaches
Along WA coast and
Puget Sound, beaches
come in many textures
and types
 Terrain includes:
 Steep bluffs
 Forested
slopes
 Beaches
 River deltas
 Tide flats
 Spits
What did the glaciers leave
behind? Primary Coasts in Puget Sound
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 Puget Sound is a fjords. Fjords are:
 Long, narrow inlets with steep sides, created in a valley
carved by glacial activity
 Long, deep narrow channels look like a U-shaped cross
section
Land
Land
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What is a sill?
 Mound of sediment debris and rubble left behind
by retreat of glacier
 forming a lip, creating a shallow entrance
 Sills located at Admiralty Inlet, Tacoma Narrows,
entrance of Hood Canal and Main Basin
sills
glacial moraine
Main Basin
sill
Admiralty Inlet
Whidbey Basin
Main Basin
Hood Canal
South Sound
The basins of Puget Sound are
fronted by sills
What did the glaciers leave behind?
Primary Coasts
 Bluffs rim most of the WA
coast and Sound shoreline
 Steep, rising 50 to 500
vertical feet high
 Many of these bluffs are
made of glacial and
interglacial deposits of sand,
gravel, silt and clay
Bluffs Nourish Beaches
Eroding bluffs provide
building materials for
beaches. Sediment or
eroded "bluff stuff" drops to
the base of the bluffs, where
it is gradually carried along
the shore by wind and
waves. These bluff sediments
help build the forms of
secondary coasts.
Bluff Erosion: How fast?
 http://www.cnn.com/video/data/2.0/video/we
ather/2009/10/13/von.wa.landslide.aerials.komo
.html
 Bluff erosion is affected by
 geology
 waves
 weather
 Rates vary from 0.1 inch to 2
feet/year
Bluff erosion occurs
naturally on Puget Sound.
Many bluffs are naturally
unstable because of soil,
slope, and water
conditions...
Landslide Hazards along Puget
Sound
 Geology
 Groundwater
 Gravity
 Wave action
 Weather
 Human actions
Landslide Hazards along Puget
Sound
 Seattle Landslides:
Winter 1996-97
 Winter storms brought a mix of
heavy rain, rapid snowmelt,
and saturated soils triggering
more than 100 slides in Seattle
Perkins Lane
Magnolia Bluff
Landslides build beaches
 Local beaches are built of sand and gravel
delivered to the shore by erosion and landslides –
 Discovery Park, Point Wilson, Dungeness,
Semiahmoo Spit, and Tolmie State Park to name
a few
Where do you
want to
vacation?
 Secondary coasts
 Beaches
 Dunes
 Spits
 Tombolos
 Sand bars
 Sea stacks
Rocky Beaches
Rock beaches are made of bedrock
and boulders too big to be moved
by currents or waves
Rocks provide homes for marine life
in cracks, crevices, and tidepools
Gravel Beaches
Gravel beaches are by far the
most common beaches in Puget
Sound and off the WA coast
A gravel beach can be made of
small boulders or mud, sand, and
gravel mixed together
Mixed gravel beaches often
harbor more marine creatures
Sand beaches
Most sandy beaches
scattered along
Puget Sound have
very little wave action
They occur near the
mouths of bays or
rivers
Mud beaches
Follow a stream or river to the coast, and you'll
often find a mud beach or mudflat. Look for
wide open tideflats and meandering tidal
channels.
Two examples of mud beaches are found at
Mud Bay in Thurston County and Fidalgo Bay in
Skagit County.
Mud beaches are only found in protected
areas because high waves and currents wash
mud away.
Dunes
 Hill of sand created and modified by the wind
 Usually run parallel to shoreline directly inland from the
beach
 Protect land from storm waves
 Can also form by the action of water flow
Deltas: streams of sediment
 Deltas form where streams and rivers
deposit sediments faster than waves
can remove them
 Rivers and streams bring sediment
down to the coasts
 Waves and currents sort these
materials
Spits
 Strip of beach which extends into deeper water
 Most spits straighten a curving shoreline
 Often form a straight ridge of sediment across a bay
 Develop in the direction of shore drift (longshore transport)
Dungeness Spit
 Longest natural sand spit in the United States
 Extending 5 miles into the Strait of Juan De Fuca
 Grown about 15 feet per year for the past 120 years
Tombolo
 Tombolo is a spit or bar connecting an island to the
mainland
 Form in areas protected by large waves
 The sediments come from the mainland beach or the
island
 A single tombolo is a single ridge connecting to an island
 A double tombolo has two ridges extending to shore.
Double tombolos can form in areas where there is a
seasonal shift in shore drift
Decatur Head, San Juan Islands
Sand bars
Bars are ridges of sand seen
when tides are low
Bars can be unstable, shifting
with storms and seasons
During storms, bars can break
the force of big wave
Sea stacks
 Small rock islands and tall, slender pinnacles
of rock
 Formed when part of a headland is eroded
by wave action
 Water weakens cracks in the headland,
causing them to collapse
Shore Shelter
 Shore forms provide homes for wildlife
 Shorebirds and gulls feed on bars, spits, and tombolos
 The river deltas, and spits provide breeding areas for fish
such as sand lance and surf smelt
 Bald eagles and other birds use drift logs on spits for
perches during the day
 In summer months, Harbor seals may give birth to and nurse
pups on bars
Drift logs on Dungeness Spit provide perches for birds
Over the Shoreline
 Bluffs and narrow beaches rim most of the
coast and Sound
 Most bluffs are made of glacial and
interglacial sediments layers of sand, cobble,
and clay
 Eroding bluffs provide most of the building
materials for beaches
Summary
Primary coasts: formed by nonmarine
processes
Secondary coasts: modified by marine
processes
Dynamic equilibrium of shoreline forms
and beaches
 Supply, removal, and longshore transport
of sediments