Lecture-21-F10

Lecture-21-F10 - EAS 111 General Announcements 11/22/10 •...

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Unformatted text preview: EAS 111 General Announcements 11/22/10 • Today: Coastlines and Coastal Processes Schedule Issues – looking ahead • This week: • • • • No labs – Thanksgiving Break Mon (11/29) = Review; Weds. (12/1) = LECTURE Exam 3 Review materials posted Extra Office hours: After class until 5 PM, Monday 11/29, and Tuesday 12/1 12:30-2:00 PM. • The week after that (12/7-10) = Dead Week = LAB Exam 3 AND our last wrap-up lecture & review Earth and Atmospheric Sciences 111 Fall 2010 Coastal Processes and Shorelines -Water meets land -Dynamics of erosion, deposition and hazards -Lecture 21 Observe factors that affect the appearance of a shoreline Storm Hardness Hardness of bedrock of Strength of waves River Amount and Amount size of sediment size 14.01.b Bay Waves ed od lley Flo va r ive R Climate Slope of Slope seafloor seafloor Orientation of coast Uplift or subsidence Wind blows Wind across the across surface (for a surface long ways to generate big waves) fetch fetch How do waves form? Waves increase Waves in size in Gas molecules collide with water to form waves to Wave Wave collapses if becomes too steep steep How Waves Are Described 14.03.a Wave base depth = ½ the wavelength = depth below which no wave action felt = depth above which waves interact with deeper water or the seafloor Breaks where wave base = ½ wavelength Breaks wave 14.03.c How Waves Interact with the Shoreline Swirl away loose pieces of bedrock Swirl or break off new pieces or Grind and break clasts, Grind making sand and stones that promote erosion that Waves bend (refract) if Waves approach shore at an angle at Part that Part encounters bottom slows, bending wave wave Waves break directly on Waves promontory from several sides sides Bay Bay Bays protected Bays from largest waves from y y orr tto on on om om Pr Pr 14.04.a-b How Sand and Other Sediment get Moved on a Beach Wind blows Wind Sand washed back Sand sand on, and forth by waves and off, or along beach beach and t of s n veme Mo 14.04.c Water flows Water downslope carrying sediment downslope Sediment Sediment moves laterally along coast if wave at angle to beach beach Washes up Washes at angle, but washes directly down slope down Michigan City Harbor Michigan City, IN North is UP on this photo: Observe the wave crests Which direction is the prevailing wind here? A.from the north B.from the south C.from the east D.from the west wave crests Gravity Wind & Waves Longshore current and Net sand transport Shoreline Features Formed by Deposition Sandbar Spit Barrier island Baymouth bar 14.05.b Observe the formation of spits, baymouth bars, and Observe barrier islands barrier Spit forms when waves and Spit longshore currents transport Spit sediment along beach sediment rrent ore cu h Longs 14.05.b7 Spit can grow into Spit baymouth bar baymouth nds ier isla Barr ent re curr ho Longs bar mouth Bay ent re curr ho Longs If sea level rises, spits If and bars may become barrier islands barrier Shoreline Features Carved by Erosion 14.05.a Sea cliffs Caves and sea arches Pinnacles and sea stacks Wave-cut platforms Consider what determines whether a shoreline gains Consider or loses sand with time or Dunes with sand Dunes Rivers provide influx Rivers mostly from beach of sediment of River River or river or Sediment largely from Sediment erosion on land erosion Dunes Delta Offshore Offshore island island nt re ur c 14.04.d1 e or sh g on L Currents Currents transport sediment along coast along Beach erosion and Beach slumping rocks add sediment to shore sediment Approaches to Shoreline Problems Sea wall and riprap Breakwater Jetty Beach nourishment 14.06.b Observe how Observe much sea level has risen and fallen in the past past 14.08.a1 Characteristics of Submergent Coasts Chesapeake Bay: Chesapeake originally a river valley originally Fjords: once glaciercarved valleys Chesapeake Chesapeake Bay Bay 14.08.c1 Coastal dunes may Coastal become barrier islands become What might happen if sea What level rises relative to land (submergent coast)? (submergent 14.08.b Hills may become Hills islands islands River valleys River may flood may Dunes and other coastal Dunes features may become offshore bars offshore Barrier Barrier islands and other types of islands may be submerged submerged Characteristics of Emergent Coasts Wave-cut notch above sea Wave-cut level level Coral reefs exposed when Coral sea level drops or land uplifted by tectonics uplifted Wave-cut platforms now Wave-cut marine terraces high above sea level above 14.08.d r ba nd Sa What might happen if sea What level falls relative to land (emergent coast)? (emergent Reef Erosion incises into Erosion beach and other land land Wave-cut Wave-cut notches and terraces exposed terraces Reefs may Reefs become exposed become Sandbars Sandbars can become coastal dunes coastal 14.08.b EAS 111: Assignment for Monday 11/29/09 • Exploring Geology • Complete all assigned readings posted on BlackBoard • Read and review the Exam 3 and Lab Exam 3 Study Guides –now posted • Be here for Monday’s review! ...
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