Coasts I can distinguish between primary and secondary coasts.
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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 What did the glaciers leave behind? Primary Coasts in Puget Sound 4 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 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
