Coasts

1
Coasts

• I can distinguish between primary and secondary
  coasts.
• I can describe different types of beaches.

2
Types of Coasts

• Primary coasts
• 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
• Erosion due to the movement of the sea
• Deposition of sediments due to movement of sea
• Stabilization due to marine plant growth

3
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

4
What did the glaciers leave behind? Primary
Coasts in Puget Sound

• 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
5
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
sill
Main Basin
glacial moraine
6
The basins of Puget Sound are fronted by sills
7
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.

8
Bluff Erosion How fast?

• Bluff erosion occurs naturally on Puget Sound.
  Many bluffs are naturally unstable because of
  soil, slope, and water conditions...

• http//www.cnn.com/video/data/2.0/video/weather/20
  09/10/13/von.wa.landslide.aerials.komo.html
• Bluff erosion is affected by
• geology
• waves
• weather
• Rates vary from 0.1 inch to 2 feet/year

9
Landslide Hazards along Puget Sound

• Geology
• Gravity
• Weather

• Groundwater
• Wave action
• Human actions

10
Landslide Hazards along Puget Sound

• Seattle LandslidesWinter 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
11
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

12
Where do you want to vacation?

• Secondary coasts
• Beaches
• Dunes
• Spits
• Tombolos
• Sand bars
• Sea stacks

13
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

14
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

15
Sand beaches

• Most sandy beaches scattered along Puget Sound
  have very little wave action
• They occur near the mouths of bays or rivers

16
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.

17
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

18
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

19
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)

20
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

21
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
22
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

23
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

24
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
25
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

26
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