Coasts

I can distinguish between primary and secondary coasts.

I can describe different types of beaches.

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

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

4What 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

glacial moraine Main Basin

sills sill

The basins of Puget Sound are fronted by sills

Hood Canal

Main Basin

Whidbey Basin

South Sound

Admiralty Inlet

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/weather/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

Gravity

Weather

Groundwater

Wave action

Human actions

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  

Landslide Hazards along Puget Sound

Perkins LaneMagnolia Bluff

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

Landslides build beaches

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