GEOLOGY 101Spring 2014Class 17

Tide wave

These are shallow water waves because wavelength is so long.

Entire water column involved Speed determined by rotation of

earth and water depth Sea basins complicate tides, huge in

some places very slight in others

"Tsunami" - a Japanese word meaning "great wave in harbor". It is a series of ocean waves commonly caused by violent movement of the sea floor by submarine faulting, landslides, or volcanic activity. A tsunami travels at the speed of nearly 500 miles per hour outward from the site of the violent movement. http://video.nationalgeographic.com/video/news/japan-tsunami-2011-vin?cs=related&source=relatedvideo

Tsunami

Tsunami terminology Often called “tidal waves” but have nothing to do

with the tides Japanese term meaning “harbor wave” Also called “seismic sea waves”

Created by movement of the ocean floor by: Underwater fault movement Underwater avalanches Underwater volcanic eruptions

Most tsunami originate from underwater fault movement

Figure 8-21a

Tsunami characteristics

Affect entire water column, so carry more energy than surface waves

Can travel at speeds over 700 kilometers (435 miles) per hour

Small wave height in the open ocean, so pass beneath ships unnoticed

Build up to extreme heights in shallow coastal areas

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Breaks where wave base = ½ wavelength

Wind blows across surface

Waves increase in size

Wave collapses if becomes too steep

How do waves form?

Bay

Promontory

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How Waves Interact with the Shoreline

Swirl away loose pieces of bedrock or break off new pieces

Grind and break clasts, making sand and stones

that promote erosionWaves bend (refract) if approach shore at an angle

Bays protected from largest waves

Waves break directly on promontory from several sidesPart that

encounters bottom slows, bending wave

SlumpMovement of sand

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How Sand and Other Sediment get Moved on a Beach

Sand washed back and forth by waves

Water flows downslope carrying sediment

Wind blows sand on, off, or along beach

Sediment moves laterally along coast if wave at angle to beach

Washes up at angle,

but washes directly

down slope

River

Dunes

Delta

Offshore island

Reef

Longsh

ore curre

nt

Currents transport

sediment along coast

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Consider what determines whether a shoreline gains or loses sand with time

Rivers provide influx of sediment

Sediment largely from erosion on land

Dunes with sand mostly from beach

or river

Reefs erode, adding material to the system

Beach erosion and slumping rocks add sediment to shore

The Beach

In some ways, the beach is nothing more than a great energy dissipation system to protect the land from the stormy sea.

Others – rock cliffs, mangrove, coral reefs, and rarely - mud Beaches –very rare SW Louisiana

Sand in beaches always moving –onshore-offshore in response to storm energy

Sand moves alongshore in response to longshore drift

Waves break when they reach shallow water and start interacting with the bottom

The importance of the dunes The dunes’ particularly the foredunes

are directly interacting with the beach and near shore sand bars.

Wind (Aeolian) and waves move sand around but where beaches exist, they work to keep the sand in place over time.

Importance of vegetation in anchoring dune – grasses and forbs can not be understated

The importance of dunes to a stable beach environment also cannot be under stated

The Dynamic Beach, dunes and offshore bars

Dune vegetation – South Padre Island

Storm Scarped Dunes on Padre Island August 2005

Sand moved from dunes during tropic storm to the offshore sand bars

Normal waves slow moves back onshore where the wind willBlow it back into the dunes where it is trapped by vegetation

Protected “dunes” at Miami

Copyright © Kathleen Walling Fry

Disappearing beaches Sand moves from a source (a river mouth

or eroding seaside cliff to a sink, either and inlet or an offshore canyon

Waves and physics keeps most of the sand in the surf zone

Dunes and dune sediment keep sand from blowing inland

If sediment supply gets reduced (dam on river, new inlet, protection of eroding cliff) sand supply washes away, erode width of beach

Groins capture some sand but cause greater erosion downdrift

Beach nourishment projects the only way out for some beaches – Miami the most famous

In the northern Gulf of Mexico, the currents move Counter clockwise, Bringing silt and mud from the Mississippi to Galveston and leaving Alabama beaches sandy

http://sofia.usgs.gov/virtual_tour/ecosystems/index.html

Red Mangrove with arching and drop roots

Black Mangrove with

http://www.finexpeditions.com/BirdsMangrove.htm

Pneumatophores that allow it to breathe

Miami Beach

Before beach replenishment

After beach replenishment

Barrier Islands

Protection for areas behind them from waves.

Extensive on the east coast of North America

Sea-level rise is forcing barrier islands landward. Many of the low-lying ones in Louisiana are disappearing.

Occasional washover in storms normal.

Galveston, Padre, Mustang, Matagorda Cape Canaveral, Miami Beach, Pensacola Beach, Sea Islands of Georgia, Outer Banks

http://www.lib.utexas.edu/maps/national_atlas_1970/ca000060.jpg

New Orleans

Mobile

Houston

Muddy waters

Louisiana Gulf Coast

Mud Coast

Louisiana Gulf Coast Near Grand Isle

Miami

Key West

West Palm Beach

Tampa

Jacksonville

Daytona Beach

Tallahassee

Orlando/Kissimmee

Cape Canaveral

Mobile Pensacola

Barrier Islands

http://images.google.com/imgres?imgurl=http://lh3.google.com/_ylmDBLJtgmc/RwLv4c3zSLI/AAAAAAAAARI/Wk9pMF4Y0Kw/s800/IMG_0346.JPG&imgrefurl=http://picasaweb.google.com/lh/photo/8LRle9SeVS11vZ5LEjR_5g&h=600&w=800&sz=110&hl=en&start=5&tbnid=VnorDMHMr-ASSM:&tbnh=107&tbnw=143&prev=/images%3Fq%3Dbeach%2Bkey%2Bwest%26gbv%3D2%26ndsp%3D20%26hl%3Den%26sa%3DN

Crushed coral beach in Key West

Panama City – no dunes left

http://www.threebestbeaches.com/florida/

Spring Break – Daytona Beach

http://www.threebestbeaches.com/florida/uploaded_images/tbb-daytona04-780348.jpg

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Shoreline Features Carved by Erosion

Sea cliffs

Wave-cut platforms

Caves and sea arches

Pinnacles and sea stacks

Objectives – Chapter 19

Explain the origin of the three kinds of ocean waves (Gravity, tidal, tsunami)

Discuss how waves and tides shape coastline features

Explain how beaches and dunes dissipate wave energy hand help protect the coastland.

Describe the evidence and consequences of rising sea levels