Shore: Junction of Land & Water. Sediments come off land Most get dumped at the beach Sediment interacts with ocean waves and currents

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Shore: Junction of Land & Water Supplemental Slides Sediments come off land Most get dumped at the beach Sediment interacts with ocean waves and currents Junction of Land & Water

1 Shore: Junction of Land & Water Supplemental Slides Sediments come off land Most get dumped at the beach Sediment interacts with ocean waves and currents Junction of Land & Water Features: Breaking waves, tides, rivers, longshore drift, rip currents, intense biological activity, changing sea levels, rising/sinking land, humanity Shorelines Constantly Changing 1

2 Shore vs. Coast Shore: line where ocean meets land Coast: zone affected by near shore processes Shape of coast: erosion by waves, sediment transport, local isostasy, etc. Location of coast: Sea Level Change Sea Level Variations Changes in Sea Level: Global Effects: Sea-floor spreading rates Global ice volume changes (Ice Ages) Global temperature variations Local Effects: Faults, warping Isostatic adjustments 2

3 Sea Level Variations a) last glacial max; b) last interglacial; c) present sea level (still slowly rising) Sea Level Variations Rising sea level for last 18,000 years 3

4 Sea Level: 18,000 years ago Sea Level: ~10,000 (?) yrs in future 4

5 Locations of Coasts Coastal locations depend primarily on global tectonics and ocean water volume Changing sea level greatly affects coastal processes Questions? 5

6 Types of Coasts Erosional Coasts: new coasts in which coastal materials are typically removed by erosion Northern and Central California, Maine Depositional Coasts: Typically slowly growing by accumulation of sediments Southern California, East & Gulf Coasts Erosional Coasts 6

$beaches because erosional debris is swept offshore Erosional Coasts Shore Straightening: Wave refraction leads to increased erosion of headlands Eventually straightens initially irregular$

7 Erosional Coasts Sea Cliffs: Due to undercutting Sea Caves: Form in weakest materials Headlands: Formed by strongest material Typical erosional shoreline has rocky cliffs with very narrow beaches because erosional debris is swept offshore Erosional Coasts Shore Straightening: Wave refraction leads to increased erosion of headlands Eventually straightens initially irregular coastlines 7

8 Central California Sea Cliffs Depositional Coasts 8

9 Depositional Coasts Typically sediments, not rocky Wide beaches common Thick layer of deposited seds can buffer coast from rapid erosion Erosional coasts evolve to depositional if tectonic activity / sea level change wanes Beaches Zones of loose sediments that cover majority of the shore Result when sediments are transported to locations suitable for deposition Constantly changing rivers of sand Sediment transport processes 9

The Coastal Zone Beach: between the erosional area above water line and the depositional area below water line Beach Currents Longshore Currents: Currents running parallel to the

10 The Coastal Zone Beach: between the erosional area above water line and the depositional area below water line Beach Currents Longshore Currents: Currents running parallel to the beach Due to slight obliquity of wave approach angle Rip Currents: Waves pile up water on the beach Water rush back out to sea in narrow jets If caught, swim parallel to shore 10

11 Beach Sediment Transport Rip Currents 11

Actual Rip Current (Green). Notice waves are nearly parallel to shore. http://science.whoi.edu/pvlab/ncex/ncex-nearshore.

12 Actual Rip Current (Green). Notice waves are nearly parallel to shore. Beach Profiles Swell Profile: Summer, low wave energy profile Broad berm, steep beach face Net accumulation of sand Storm Profile: Winter, high wave energy profile Eroded berm, narrow shallow beach Eroded beach material accumulates in longshore bars Larger grain sizes left over, smaller grains transported to bars 12

13 Beach Profiles Beach Profiles Typically, finer grained beaches have shallower slopes Coarse grained beaches are steeper in slope Angle of repose of the grains Porosity of the sediments 13

14 Questions & Comments? Beach Sand Budgets Like balancing a check book Real beaches are rarely in a steady state 14

15 Sand Budgets Sand Budgets: Coastal Cells 15

16 Sand Budgets: Los Angeles Coastal Cells Coastal Cells Large cells form on smooth passive margins (Atlantic) Smaller cells along active marginal coasts (Pacific) 16

17 Questions Features of Depositional Environments Sand Dunes Barrier Islands River Deltas 17

18 Sand Dunes Wind blown sand gets deposited in backshore dunes Debit in the sand budget Grasses, Beach plants anchor dunes Sand Dunes 18

19 Barrier Islands Typically along Passive, Depositional Margins Up to 200 km in length (Galveston Is.) Can form due to changing sea level or as cut off sand spits Rapidly changing: dangerous real estate Popular Vacation Locations: Ocean City, MD; Padre Island, TX Buildings destroy the dunes & vegetation that hold islands together Barrier Islands 19

Barrier Islands Barrier Islands http://woodshole.er.usgs.

htm River Deltas Discharge of sediment from the mouths

20 Barrier Islands Barrier Islands River Deltas Discharge of sediment from the mouths of rivers into estuaries or the ocean Produce big sedimentary fans 20

21 Mississippi River Delta (before Katrina) Distributaries Fig 11-19a, p.211 Questions 21

Estuaries Semi-enclosed bodies containing a mix of freshwater and seawater Drowned River Valleys Chesapeake Bay, MD; Sydney Harbor, AU Tectonic Control SF

22 Estuaries Semi-enclosed bodies containing a mix of freshwater and seawater Drowned River Valleys Chesapeake Bay, MD; Sydney Harbor, AU Tectonic Control SF Bay is a fault bounded estuary Glacier Cut Fjords Hudson River Valley Typically areas of high bioproductivity nutrients washed in by rivers Fig 11-22, p

23 Fig 11-6, p.202 Salinity in the Chesapeake 23

24 Questions Humanity vs. The Coasts 1. People build by the beach 2. The beach tends to move 3. People try to keep the beach from moving 24

25 Humanity vs. The Coasts Beach Stabilization Techniques: Redirection of wave energy Breakwaters: Out from shore Seawalls: At the shoreline Redirection of longshore transport Groins: Outward from beaches Jetties: At mouths of rivers, inlets, harbors, etc. Beach Nourishment: Artificially dumping sand on a eroding beach Humanity vs. The Coasts Shoreline stabilization efforts typically do not work for very long Beaches are too dynamic Generally human intervention makes things worse or generates new unforeseen problems i.e., aggravated erosion 25

26 Humanity vs. The Coasts Where is this? Fig 11-26a, p

27 Fig 11-26b, p.216 Beach Nourishment 27

Beach Nourishment Sand is barged or trucked in and added to b each.

Santa Barbara s West Beach Waves quickly erode sand, beaches disappear unless a sand source is

Freudenrich The Dynamic Coasts Coastlines are variable structures Location varies with tectonics,

28 Beach Nourishment Sand is barged or trucked in and added to b each. Example: Upham Beach, Florida Top: Before Middle: Just After Bottom: 1 Year Later Another example: Santa Barbara s West Beach Waves quickly erode sand, beaches disappear unless a sand source is available (natural or human) Images: C. Freudenrich The Dynamic Coasts Coastlines are variable structures Location varies with tectonics, ocean water volume, etc. Shape due to various processes, local and complex Beaches change with wave activity and sediment transport processes Humans rarely are able to increase the stability of the coastlines 28

29 Questions 29

Supplemental Slides. Shore: Junction of Land & Water. Junction of Land & Water. Sea Level Variations. Shore vs. Coast. Sea Level Variations

Supplemental Slides. Shore: Junction of Land & Water. Junction of Land & Water. Sea Level Variations. Shore vs. Coast. Sea Level Variations Shore: Junction of Land & Water Supplemental Slides Sediments come off land Most get dumped at the beach Sediment interacts with ocean waves and currents Junction of Land & Water Features: Breaking waves,